Showing papers in "Hydrology and Earth System Sciences in 2019"
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TL;DR: A strong case can be made for moving away from ad hoc use of aggregated efficiency metrics and towards a framework based on purpose-dependent evaluation metrics and benchmarks that allows for more robust model adequacy assessment.
Abstract: . A traditional metric used in hydrology to summarize model
performance is the Nash–Sutcliffe efficiency (NSE). Increasingly an
alternative metric, the Kling–Gupta efficiency (KGE), is used instead. When
NSE is used, NSE = 0 corresponds to using the mean flow as a benchmark
predictor. The same reasoning is applied in various studies that use KGE as
a metric: negative KGE values are viewed as bad model performance, and only
positive values are seen as good model performance. Here we show that using
the mean flow as a predictor does not result in KGE = 0, but instead KGE = 1 - √ 2 ≈ - 0.41 . Thus, KGE values greater than −0.41
indicate that a model improves upon the mean flow benchmark – even if the
model's KGE value is negative. NSE and KGE values cannot be directly
compared, because their relationship is non-unique and depends in part on
the coefficient of variation of the observed time series. Therefore,
modellers who use the KGE metric should not let their understanding of NSE
values guide them in interpreting KGE values and instead develop new
understanding based on the constitutive parts of the KGE metric and the
explicit use of benchmark values to compare KGE scores against. More
generally, a strong case can be made for moving away from ad hoc use of
aggregated efficiency metrics and towards a framework based on
purpose-dependent evaluation metrics and benchmarks that allows for more
robust model adequacy assessment.
524 citations
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TL;DR: In this article, the authors evaluated the performance of 26 gridded (sub-) daily P datasets to obtain a view into the merit of these innovations using the Kling-Gupta efficiency (KGE).
Abstract: . New precipitation ( P ) datasets are released regularly, following
innovations in weather forecasting models, satellite retrieval methods, and
multi-source merging techniques. Using the conterminous US as a case study,
we evaluated the performance of 26 gridded (sub-)daily P datasets to obtain
insight into the merit of these innovations. The evaluation was performed at
a daily timescale for the period 2008–2017 using the Kling–Gupta efficiency
(KGE), a performance metric combining correlation, bias, and variability. As
a reference, we used the high-resolution (4 km) Stage-IV gauge-radar P
dataset. Among the three KGE components, the P datasets performed worst
overall in terms of correlation (related to event identification). In terms
of improving KGE scores for these datasets, improved P totals (affecting
the bias score) and improved distribution of P intensity (affecting the
variability score) are of secondary importance. Among the 11 gauge-corrected
P datasets, the best overall performance was obtained by MSWEP V2.2,
underscoring the importance of applying daily gauge corrections and
accounting for gauge reporting times. Several uncorrected P datasets
outperformed gauge-corrected ones. Among the 15 uncorrected P datasets, the
best performance was obtained by the ERA5-HRES fourth-generation reanalysis,
reflecting the significant advances in earth system modeling during the last
decade. The (re)analyses generally performed better in winter than in summer,
while the opposite was the case for the satellite-based datasets. IMERGHH V05
performed substantially better than TMPA-3B42RT V7, attributable to the many
improvements implemented in the IMERG satellite P retrieval algorithm.
IMERGHH V05 outperformed ERA5-HRES in regions dominated by convective storms,
while the opposite was observed in regions of complex terrain. The ERA5-EDA
ensemble average exhibited higher correlations than the ERA5-HRES
deterministic run, highlighting the value of ensemble modeling. The WRF
regional convection-permitting climate model showed considerably more
accurate P totals over the mountainous west and performed best among the
uncorrected datasets in terms of variability, suggesting there is merit in
using high-resolution models to obtain climatological P statistics. Our
findings provide some guidance to choose the most suitable P dataset for a
particular application.
291 citations
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TL;DR: This paper proposes an adaption to the standard LSTM architecture, which it is called an Entity-Aware-L STM (EA-LSTM), that allows for learning catchment similarities as a feature layer in a deep learning model and shows that these learned caughtment similarities correspond well to what the authors would expect from prior hydrological understanding.
Abstract: . Regional rainfall–runoff modeling is an old but still mostly outstanding problem in the hydrological sciences. The problem currently is that traditional hydrological models degrade significantly in performance when calibrated for multiple basins together instead of for a single basin alone. In this paper, we propose a novel, data-driven approach using Long Short-Term Memory networks (LSTMs) and demonstrate that under a “big data” paradigm, this is not necessarily the case. By training a single LSTM model on 531 basins from the CAMELS dataset using meteorological time series data and static catchment attributes, we were able to significantly improve performance compared to a set of several different hydrological benchmark models. Our proposed approach not only significantly outperforms hydrological models that were calibrated regionally, but also achieves better performance than hydrological models that were calibrated for each basin individually. Furthermore, we propose an adaption to the standard LSTM architecture, which we call
an Entity-Aware-LSTM (EA-LSTM), that allows for learning catchment similarities as a
feature layer in a deep learning model. We show that these learned catchment
similarities correspond well to what we would expect from prior hydrological
understanding.
258 citations
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TL;DR: In this article, the seasonal origins of waters in soils and trees by comparing their midsummer isotopic signatures ( δ2H ) to seasonal isotopiccycles in precipitation, using a new seasonal origin index.
Abstract: . Rain recharges soil water storages and either percolates
downward into aquifers and streams or is returned to the atmosphere through
evapotranspiration. Although it is commonly assumed that summer rainfall
recharges plant-available water during the growing season, the seasonal
origins of water used by plants have not been systematically explored. We
characterize the seasonal origins of waters in soils and trees by comparing
their midsummer isotopic signatures ( δ2H ) to seasonal isotopic
cycles in precipitation, using a new seasonal origin index. Across 182 Swiss
forest sites, xylem water isotopic signatures show that summer rain was not
the predominant water source for midsummer transpiration in any of the three
sampled tree species. Beech and oak mostly used winter precipitation, whereas
spruce used water of more diverse seasonal origins. Even in the same plots,
beech consistently used more winter precipitation than spruce, demonstrating
consistent niche partitioning in the rhizosphere. All three species' xylem
water isotopes indicate that trees used more winter precipitation in drier
regions, potentially mitigating their vulnerability to summer droughts. The
widespread occurrence of winter isotopic signatures in midsummer xylem
implies that growing-season rainfall may have minimally recharged the soil
water storages that supply tree growth, even across diverse humid climates
(690–2068 mm annual precipitation). These results challenge common
assumptions concerning how water flows through soils and is accessed by
trees. Beyond these ecological and hydrological implications, our findings
also imply that stable isotopes of δ18O and δ2H in plant
tissues, which are often used in climate reconstructions, may not reflect
water from growing-season climates.
157 citations
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TL;DR: In this article, the performance of 36 coupled model intercomparison project 5 (CMIP5) GCMs was evaluated in relation to their skills in simulating mean annual, monsoon, winter, pre-monsoon, and postmonsoon precipitation and maximum and minimum temperature over Pakistan using state-of-the-art spatial metrics, SPAtial EFficiency, fractions skill score, Goodman-Kruskal's lambda, Cramer's V, Mapcurves, and Kling-Gupta efficiency, for the period 1961-2005.
Abstract: . The climate modelling community has trialled a large
number of metrics for evaluating the temporal performance of general circulation
models (GCMs), while very little attention has been given to the assessment
of their spatial performance, which is equally important. This study
evaluated the performance of 36 Coupled Model Intercomparison Project 5
(CMIP5) GCMs in relation to their skills in simulating mean annual, monsoon,
winter, pre-monsoon, and post-monsoon precipitation and maximum and minimum
temperature over Pakistan using state-of-the-art spatial metrics, SPAtial
EFficiency, fractions skill score, Goodman–Kruskal's lambda, Cramer's V,
Mapcurves, and Kling–Gupta efficiency, for the period 1961–2005. The
multi-model ensemble (MME) precipitation and maximum and minimum temperature
data were generated through the intelligent merging of simulated
precipitation and maximum and minimum temperature of selected GCMs employing
random forest (RF) regression and simple mean (SM) techniques. The results indicated
some differences in the ranks of GCMs for different spatial metrics. The
overall ranks indicated NorESM1-M, MIROC5, BCC-CSM1-1, and ACCESS1-3 as the
best GCMs in simulating the spatial patterns of mean annual, monsoon,
winter, pre-monsoon, and post-monsoon precipitation and maximum and minimum
temperature over Pakistan. MME precipitation and maximum and minimum
temperature generated based on the best-performing GCMs showed more
similarities with observed precipitation and maximum and minimum temperature
compared to precipitation and maximum and minimum temperature simulated by
individual GCMs. The MMEs developed using RF displayed better performance
than the MMEs based on SM. Multiple spatial metrics have been used for the
first time for selecting GCMs based on their capability to mimic the spatial
patterns of annual and seasonal precipitation and maximum and minimum
temperature. The approach proposed in the present study can be extended to
any number of GCMs and climate variables and applicable to any region for
the suitable selection of an ensemble of GCMs to reduce uncertainties in
climate projections.
117 citations
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TL;DR: In this paper, the authors simulate the distribution of average evapotranspiration and streamflow at high resolution (1 km 2 ) by combining (a) a steady-state Budyko model for water balance partitioning constrained by long-term (lysimeter) observations across different land use types, (b) a novel decadal high-resolution historical land use reconstruction, and (c) gridded observations of key meteorological variables.
Abstract: . Since the 1950s, Europe has undergone large shifts in climate and land cover. Previous assessments of past and future changes in evapotranspiration or streamflow have either focussed on land use/cover or climate contributions or on individual catchments under specific climate conditions, but not on all aspects at larger scales. Here, we aim to understand how decadal changes in climate (e.g. precipitation, temperature) and land use (e.g. deforestation/afforestation, urbanization) have impacted the amount and distribution of water resource availability (both evapotranspiration and streamflow) across Europe since the 1950s. To this end, we simulate the distribution of average evapotranspiration and streamflow at high resolution (1 km 2 ) by combining (a) a steady-state Budyko model for water balance partitioning constrained by long-term (lysimeter) observations across different land use types, (b) a novel decadal high-resolution historical land use reconstruction, and (c) gridded observations of key meteorological variables. The continental-scale patterns in the simulations agree well with coarser-scale observation-based estimates of evapotranspiration and also with observed changes in streamflow from small basins across Europe. We find that strong shifts in the continental-scale patterns of evapotranspiration and streamflow have occurred between the period around 1960 and 2010. In much of central-western Europe, our results show an increase in evapotranspiration of the order of 5 %–15 % between 1955–1965 and 2005–2015, whereas much of the Scandinavian peninsula shows increases exceeding 15 %. The Iberian Peninsula and other parts of the Mediterranean show a decrease of the order of 5 %–15 %. A similar north–south gradient was found for changes in streamflow, although changes in central-western Europe were generally small. Strong decreases and increases exceeding 45 % were found in parts of the Iberian and Scandinavian peninsulas, respectively. In Sweden, for example, increased precipitation is a larger driver than large-scale reforestation and afforestation, leading to increases in both streamflow and evapotranspiration. In most of the Mediterranean, decreased precipitation combines with increased forest cover and potential evapotranspiration to reduce streamflow. In spite of considerable local- and regional-scale complexity, the response of net actual evapotranspiration to changes in land use, precipitation, and potential evaporation is remarkably uniform across Europe, increasing by ∼ 35–60 km 3 yr −1 , equivalent to the discharge of a large river. For streamflow, effects of changes in precipitation ( ∼ 95 km 3 yr −1 ) dominate land use and potential evapotranspiration contributions ( ∼ 45–60 km 3 yr −1 ). Locally, increased forest cover, forest stand age, and urbanization have led to significant decreases and increases in available streamflow, even in catchments that are considered to be near-natural.
114 citations
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TL;DR: In this paper, the authors investigated plant water sources of an emblematic refugial population of Fagus sylvatica (L.) in the Ciron river gorges in south-western France usingstable water isotopes.
Abstract: . We investigated plant water sources of an emblematic refugial
population of Fagus sylvatica (L.) in the Ciron river gorges in south-western France using
stable water isotopes. It is generally assumed that no isotopic
fractionation occurs during root water uptake, so that the isotopic
composition of xylem water effectively reflects that of source water.
However, this assumption has been called into question by recent studies
that found that, at least at some dates during the growing season, plant
water did not reflect any mixture of the potential water sources. In this
context, highly resolved datasets covering a range of environmental
conditions could shed light on possible plant–soil fractionation processes
responsible for this phenomenon. In this study, the hydrogen ( δ2H ) and oxygen ( δ18O ) isotope compositions of all
potential tree water sources and xylem water were measured fortnightly over
an entire growing season. Using a Bayesian isotope mixing model (MixSIAR),
we then quantified the relative contribution of water sources for F. sylvatica and
Quercus robur (L.) trees. Based on δ18O data alone, both species used a mix
of top and deep soil water over the season, with Q. robur using deeper soil water
than F. sylvatica. The contribution of stream water appeared to be marginal despite the
proximity of the trees to the stream, as already reported for other riparian
forests. Xylem water δ18O could always be interpreted as a
mixture of deep and shallow soil waters, but the δ2H of xylem
water was often more depleted than the considered water sources. We argue
that an isotopic fractionation in the unsaturated zone and/or within the
plant tissues could underlie this unexpected relatively depleted δ2H of xylem water, as already observed in halophytic and xerophytic
species. By means of a sensitivity analysis, we found that the estimation of
plant water sources using mixing models was strongly affected by this
δ2H depletion. A better understanding of what causes this
isotopic separation between xylem and source water is urgently needed.
94 citations
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TL;DR: In this paper, the authors combine surface moisture retrievals from the spaceborne SMAP, AMSR2 and ASCAT microwave sensors with modeled soil moisture from MERRA-2 reanalysis to estimate the actual amount of irrigation water applied.
Abstract: . Effective agricultural water management requires accurate and timely
information on the availability and use of irrigation water. However, most
existing information on irrigation water use ( IWU ) lacks the
objectivity and spatiotemporal representativeness needed for operational
water management and meaningful characterization of land–climate
interactions. Although optical remote sensing has been used to map the area
affected by irrigation, it does not physically allow for the estimation of
the actual amount of irrigation water applied. On the other hand, microwave
observations of the moisture content in the top soil layer are directly
influenced by agricultural irrigation practices and thus potentially allow
for the quantitative estimation of IWU. In this study, we combine surface
soil moisture (SM) retrievals from the spaceborne SMAP, AMSR2 and
ASCAT microwave sensors with modeled soil moisture from MERRA-2 reanalysis to
derive monthly IWU dynamics over the contiguous United States (CONUS) for the
period 2013–2016. The methodology is driven by the assumption that the
hydrology formulation of the MERRA-2 model does not account for irrigation,
while the remotely sensed soil moisture retrievals do contain an irrigation
signal. For many CONUS irrigation hot spots, the estimated spatial irrigation
patterns show good agreement with a reference data set on irrigated areas.
Moreover, in intensively irrigated areas, the temporal dynamics of observed
IWU is meaningful with respect to ancillary data on local irrigation
practices. State-aggregated mean IWU volumes derived from the combination of
SMAP and MERRA-2 soil moisture show a good correlation with statistically
reported state-level irrigation water withdrawals (IWW) but systematically
underestimate them. We argue that this discrepancy can be mainly attributed
to the coarse spatial resolution of the employed satellite soil moisture
retrievals, which fails to resolve local irrigation practices. Consequently,
higher-resolution soil moisture data are needed to further enhance the
accuracy of IWU mapping.
93 citations
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TL;DR: In this paper, the authors evaluate the performance of three performance metrics: Nash-Sutcliffe efficiency (NSE), KGE, and APFB, and conclude that NSE-based model calibrations actually result in poor production of high-flow events, such as the annual peak flows used for flood frequency estimation.
Abstract: . Calibration is an essential step for improving
the accuracy of simulations generated using hydrologic models. A key modeling
decision is selecting the performance metric to be optimized. It has been
common to use squared error performance metrics, or normalized variants such
as Nash–Sutcliffe efficiency (NSE), based on the idea that their
squared-error nature will emphasize the estimates of high flows. However, we
conclude that NSE-based model calibrations actually result in poor
reproduction of high-flow events, such as the annual peak flows that are used
for flood frequency estimation. Using three different types of performance
metrics, we calibrate two hydrological models at a daily step, the Variable
Infiltration Capacity (VIC) model and the mesoscale Hydrologic Model (mHM),
and evaluate their ability to simulate high-flow events for 492 basins
throughout the contiguous United States. The metrics investigated are
(1) NSE, (2) Kling–Gupta efficiency (KGE) and its variants, and (3) annual
peak flow bias (APFB), where the latter is an application-specific metric
that focuses on annual peak flows. As expected, the APFB metric produces the
best annual peak flow estimates; however, performance on other
high-flow-related metrics is poor. In contrast, the use of NSE results in
annual peak flow estimates that are more than 20 % worse, primarily due
to the tendency of NSE to underestimate observed flow variability. On the
other hand, the use of KGE results in annual peak flow estimates that are
better than from NSE, owing to improved flow time series metrics (mean and
variance), with only a slight degradation in performance with respect to
other related metrics, particularly when a non-standard weighting of the
components of KGE is used. Stochastically generated ensemble simulations
based on model residuals show the ability to improve the high-flow metrics,
regardless of the deterministic performances. However, we emphasize that
improving the fidelity of streamflow dynamics from deterministically
calibrated models is still important, as it may improve high-flow metrics
(for the right reasons). Overall, this work highlights the need for a deeper
understanding of performance metric behavior and design in relation to the
desired goals of model calibration.
90 citations
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TL;DR: In this paper, an integrated approach to evaluate inundation risks is presented, in which an algorithm is proposed to integrate the storm water management model (SWMM) into a geographical information system (GIS).
Abstract: . This study presents an integrated approach to evaluate inundation
risks, in which an algorithm is proposed to integrate the storm water
management model (SWMM) into a geographical information system (GIS). The
proposed algorithm simulates the flood inundation of overland flows and in
metro stations for each designed scenario. It involves the following stages:
(i) determination of the grid location and spreading coefficient and (ii) an
iterative calculation of the spreading process. In addition, an equation is
proposed to calculate the inundation around a metro station and to predict
the potential inundation risks of the metro system. The proposed method is
applied to simulate the inundation risk of the metro system in the urban
centre of Shanghai under 50-year, 100-year, and 500-year rainfall
intensities. Both inundation extent and depth are obtained and the proposed
method is validated with records of historical floods. The results
demonstrate that in the case of a 500-year rainfall intensity, the inundated
area with a water depth excess of 300 mm covers up to 5.16 km 2 . In
addition, four metro stations are inundated to a depth of over 300 mm.
88 citations
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TL;DR: In this paper, a general parametric reservoir operation model based on piecewise-linear relationships between reservoir storage, inflow, and release is proposed to approximate actual reservoir operations, which can be integrated into any H-LSM.
Abstract: . Reservoirs significantly affect flow regimes in watershed systems by changing the magnitude and timing of streamflows. Failure to represent these effects limits the performance of hydrological and land-surface models (H-LSMs) in the many highly regulated basins across the globe
and limits the applicability of such models to investigate the futures of
watershed systems through scenario analysis (e.g., scenarios of climate,
land use, or reservoir regulation changes). An adequate representation of
reservoirs and their operation in an H-LSM is therefore essential for a
realistic representation of the downstream flow regime. In this paper, we
present a general parametric reservoir operation model based on piecewise-linear relationships between reservoir storage, inflow, and release to
approximate actual reservoir operations. For the identification of the model
parameters, we propose two strategies: (a) a “generalized”
parameterization that requires a relatively limited amount of data and
(b) direct calibration via multi-objective optimization when more data on
historical storage and release are available. We use data from 37 reservoir
case studies located in several regions across the globe for developing and
testing the model. We further build this reservoir operation model into the
MESH (Modelisation Environmentale-Surface et Hydrologie) modeling system, which is a large-scale H-LSM. Our results across the
case studies show that the proposed reservoir model with both
parameter-identification strategies leads to improved simulation accuracy
compared with the other widely used approaches for reservoir operation
simulation. We further show the significance of enabling MESH with this
reservoir model and discuss the interdependent effects of the simulation
accuracy of natural processes and that of reservoir operations on the overall
model performance. The reservoir operation model is generic and can be
integrated into any H-LSM.
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TL;DR: In this paper, the authors investigated the potential for compound flooding arising from the joint occurrence of high storm surge and high river discharge around the coast of the UK and found that there will be a spatial variation in compound flood frequency, with some coastal regions experiencing a greater dependency between the two flooding sources than other regions.
Abstract: . In low-lying coastal regions, flooding arises from oceanographic (storm
surges plus tides and/or waves), fluvial (increased river discharge), and/or
pluvial (direct surface run-off) sources. The adverse consequences of a flood
can be disproportionately large when these different sources occur
concurrently or in close succession, a phenomenon that is known as
“compound flooding”. In this paper, we assess the potential for compound
flooding arising from the joint occurrence of high storm surge and high
river discharge around the coast of the UK. We hypothesise that there will be
spatial variation in compound flood frequency, with some coastal regions
experiencing a greater dependency between the two flooding sources than
others. We map the dependence between high skew surges and high river
discharge, considering 326 river stations linked to 33 tide gauge sites. We
find that the joint occurrence of high skew surges and high river discharge
occurs more frequently during the study period (15–50 years) at sites on the
south-western and western coasts of the UK (between three and six joint events per
decade) compared to sites along the eastern coast (between zero and one joint
events per decade). Second, we investigate the meteorological conditions
that drive compound and non-compound events across the UK. We show, for the
first time, that spatial variability in the dependence and number of joint
occurrences of high skew surges and high river discharge is driven by
meteorological differences in storm characteristics. On the western coast of
the UK, the storms that generate high skew surges and high river discharge
are typically similar in characteristics and track across the UK on
comparable pathways. In contrast, on the eastern coast, the storms that
typically generate high skew surges are mostly distinct from the types of
storms that tend to generate high river discharge. Third, we briefly examine
how the phase and strength of dependence between high skew surge and high
river discharge is influenced by the characteristics (i.e. flashiness, size,
and elevation gradient) of the corresponding river catchments. We find that high
skew surges tend to occur more frequently with high river discharge at
catchments with a lower base flow index, smaller catchment area, and steeper
elevation gradient. In catchments with a high base flow index, large
catchment area, and shallow elevation gradient, the peak river flow tends to
occur several days after the high skew surge. The previous lack of
consideration of compound flooding means that flood risk has likely been
underestimated around UK coasts, particularly along the south-western and western
coasts. It is crucial that this be addressed in future assessments of flood
risk and flood management approaches.
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TL;DR: In this article, the Soil and Water Assessment Tool (SWAT) with satellite-based actual evapotranspiration (AET) data from the Global Land Evolution Evaporation Amsterdam Model (GLEAM_v3.0a) and from the Moderate Resolution Imaging Spectroradiometer Global Evapolation (MOD16) for the Ogun River Basin was used to calibrate and validate an eco-hydrological model for data-scarce catchment.
Abstract: . The main objective of this study was to calibrate and validate the
eco-hydrological model Soil and Water Assessment Tool (SWAT) with
satellite-based actual evapotranspiration (AET) data from the Global Land
Evaporation Amsterdam Model (GLEAM_v3.0a) and from the Moderate Resolution
Imaging Spectroradiometer Global Evaporation (MOD16) for the Ogun River Basin
(20 292 km 2 ) located in southwestern Nigeria. Three potential
evapotranspiration (PET) equations (Hargreaves, Priestley–Taylor and
Penman–Monteith) were used for the SWAT simulation of AET. The reference
simulations were the three AET variables simulated with SWAT before model
calibration took place. The sequential uncertainty fitting technique (SUFI-2)
was used for the SWAT model sensitivity analysis, calibration, validation and
uncertainty analysis. The GLEAM_v3.0a and MOD16 products were subsequently
used to calibrate the three SWAT-simulated AET variables, thereby obtaining
six calibrations–validations at a monthly timescale. The model performance
for the three SWAT model runs was evaluated for each of the 53 subbasins
against the GLEAM_v3.0a and MOD16 products, which enabled the best model run
with the highest-performing satellite-based AET product to be chosen. A
verification of the simulated AET variable was carried out by (i) comparing
the simulated AET of the calibrated model to GLEAM_v3.0b AET, which is a
product that has different forcing data than the version of GLEAM used for
the calibration, and (ii) assessing the long-term average annual and average
monthly water balances at the outlet of the watershed. Overall, the SWAT
model, composed of the Hargreaves PET equation and calibrated using the
GLEAM_v3.0a data (GS1), performed well for the simulation of AET and
provided a good level of confidence for using the SWAT model as a decision
support tool. The 95 % uncertainty of the SWAT-simulated variable
bracketed most of the satellite-based AET data in each subbasin. A validation
of the simulated soil moisture dynamics for GS1 was carried out using
satellite-retrieved soil moisture data, which revealed good agreement. The
SWAT model (GS1) also captured the seasonal variability of the water balance
components at the outlet of the watershed. This study demonstrated the potential to use remotely sensed
evapotranspiration data for hydrological model calibration and validation in
a sparsely gauged large river basin with reasonable accuracy. The novelty of
the study is the use of these freely available satellite-derived AET
datasets to effectively calibrate and validate an eco-hydrological model for
a data-scarce catchment.
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TL;DR: In this article, the authors present a framework for selecting suitable paired catchments for the study of the human influence on hydrological drought, which is based on the classic hydrology approach that was developed in the 1920s for assessing the impact of land cover treatment on water quantity and quality.
Abstract: . Quantifying the influence of human activities, such as reservoir building, water abstraction, and land use change, on hydrology is crucial for sustainable future water management, especially during drought. Model-based methods are very time-consuming to set up and require a good understanding of human processes and time series of water abstraction, land use change, and water infrastructure and management, which often are not available. Therefore, observation-based methods are being developed that give an indication of the direction and magnitude of the human influence on hydrological drought based on limited data. We suggest adding to those methods a “paired-catchment” approach, based on the classic hydrology approach that was developed in the 1920s for assessing the impact of land cover treatment on water quantity and quality. When applying the paired-catchment approach to long-term pre-existing human influences trying to detect an influence on extreme events such as droughts, a good catchment selection is crucial. The disturbed catchment needs to be paired with a catchment that is similar in all aspects except for the human activity under study, in that way isolating the effect of that specific activity. In this paper, we present a framework for selecting suitable paired catchments for the study of the human influence on hydrological drought. Essential elements in this framework are the availability of qualitative information on the human activity under study (type, timing, and magnitude), and the similarity of climate, geology, and other human influences between the catchments. We show the application of the framework on two contrasting case studies, one impacted by groundwater abstraction and one with a water transfer from another region. Applying the paired-catchment approach showed how the groundwater abstraction aggravated streamflow drought by more than 200 % for some metrics (total drought duration and total drought deficit) and the water transfer alleviated droughts with 25 % to 80 %, dependent on the metric. Benefits of the paired-catchment approach are that climate variability between pre- and post-disturbance periods does not have to be considered as the same time periods are used for analysis, and that it avoids assumptions considered when partly or fully relying on simulation modelling. Limitations of the approach are that finding a suitable catchment pair can be very challenging, often no pre-disturbance records are available to establish the natural difference between the catchments, and long time series of hydrological data are needed to robustly detect the effect of the human activities on hydrological drought. We suggest that the approach can be used for a first estimate of the human influence on hydrological drought, to steer campaigns to collect more data, and to complement and improve other existing methods (e.g. model-based or large-sample approaches).
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TL;DR: In this article, an intercomparison of eight different global hydrological models (GHMs) from collaborators of the Global Flood Partnership (GFP) for simulating catastrophic flooding in the Amazon basin is presented.
Abstract: . Extreme flooding impacts millions of people that live within the
Amazon floodplain. Global hydrological models (GHMs) are frequently used to
assess and inform the management of flood risk, but knowledge on the skill
of available models is required to inform their use and development. This
paper presents an intercomparison of eight different GHMs freely available
from collaborators of the Global Flood Partnership (GFP) for simulating
floods in the Amazon basin. To gain insight into the strengths and
shortcomings of each model, we assess their ability to reproduce daily and
annual peak river flows against gauged observations at 75 hydrological
stations over a 19-year period (1997–2015). As well as highlighting regional variability in the accuracy of simulated streamflow, these results indicate that (a) the meteorological input is the dominant control on the accuracy of both daily and annual maximum river flows, and (b) groundwater and routing calibration of Lisflood based on daily river flows has no impact on the ability to simulate flood peaks for the chosen river basin. These findings have important relevance for applications of large-scale hydrological models, including analysis of the impact of climate variability, assessment of the influence of long-term changes such as land-use and anthropogenic climate change, the assessment of flood likelihood, and for flood forecasting systems.
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TL;DR: In this article, a multivariate bias correction-based approach was used to estimate the relationship between air temperature and precipitation in a partially glacierized alpine catchments, and the results showed that incorporating or ignoring the inter-variable relationships between precipitation and air temperature can impact the conclusions drawn in hydrological climate change impact studies.
Abstract: . Alpine catchments show a high sensitivity to climate
variation as they include the elevation range of the snow line. Therefore,
the correct representation of climate variables and their interdependence is
crucial when describing or predicting hydrological processes. When using
climate model simulations in hydrological impact studies, forcing
meteorological data are usually downscaled and bias corrected, most often by
univariate approaches such as quantile mapping of individual variables,
neglecting the relationships that exist between climate variables. In this
study we test the hypothesis that the explicit consideration of the relation
between air temperature and precipitation will affect hydrological impact
modelling in a snow-dominated mountain environment. Glacio-hydrological
simulations were performed for two partly glacierized alpine catchments
using a recently developed multivariate bias correction method to
post-process EURO-CORDEX regional climate model outputs between 1976 and
2099. These simulations were compared to those obtained by using the common
univariate quantile mapping for bias correction. As both methods correct
each climate variable's distribution in the same way, the marginal
distributions of the individual variables show no differences. Yet,
regarding the interdependence of precipitation and air temperature, clear
differences are notable in the studied catchments. Simultaneous correction
based on the multivariate approach led to more precipitation below air
temperatures of 0 ∘ C and therefore more simulated snowfall than
with the data of the univariate approach. This difference translated to
considerable consequences for the hydrological responses of the catchments.
The multivariate bias-correction-forced simulations showed distinctly
different results for projected snow cover characteristics, snowmelt-driven
streamflow components, and expected glacier disappearance dates. In all
aspects – the fraction of precipitation above and below 0 ∘ C,
the simulated snow water equivalents, glacier volumes, and the streamflow
regime – simulations resulting from the multivariate-corrected data
corresponded better with reference data than the results of univariate bias
correction. Differences in simulated total streamflow due to the different
bias correction approaches may be considered negligible given the generally
large spread of the projections, but systematic differences in the
seasonally delayed streamflow components from snowmelt in particular will
matter from a planning perspective. While this study does not allow
conclusive evidence that multivariate bias correction approaches are
generally preferable, it clearly demonstrates that incorporating or ignoring
inter-variable relationships between air temperature and precipitation data
can impact the conclusions drawn in hydrological climate change impact
studies in snow-dominated environments.
••
TL;DR: In this article, the authors evaluated the long-term changes in spatiotemporal patterns of annually and seasonal aridity during two major crop growing seasons of Pakistan, Kharif and Rabi, using gridded precipitation and potential evapotranspiration (PET) data.
Abstract: . The changing characteristics of aridity over a larger
spatiotemporal scale have gained interest in recent years due to climate
change. The long-term (1901–2016) changes in spatiotemporal patterns of
annual and seasonal aridity during two major crop growing seasons of
Pakistan, Kharif and Rabi, are evaluated in this study using gridded
precipitation and potential evapotranspiration (PET) data. The UNESCO aridity
index was used to estimate aridity at each grid point for all the years
between 1901 and 2016. The temporal changes in aridity and its associations
with precipitation and PET are evaluated by implementing a moving window of
50 years of data with an 11-year interval. The modified Mann–Kendall (MMK) trend
test is applied to estimate unidirectional change by eliminating the effect
of natural variability of climate, and Pettitt's test is used to detect
year of change in aridity. The results revealed that the climate over 60 % of
Pakistan (mainly in southern parts) is arid. The spatial patterns of aridity
trends show a strong influence of the changes in precipitation on the aridity
trend. The increasing trend in aridity (drier) is noticed in the southwest,
where precipitation is low during Kharif, while there is a decreasing trend (wetter)
in the Rabi season in the region which receives high precipitation due to
western disturbances. The annual and Kharif aridity is found to decrease
(wetter) at a rate of 0.0001 to 0.0002 per year in the northeast, while
Kharif and Rabi aridity are found to increase (drier) at some locations in
the south at a rate of −0.0019 to −0.0001 per year. The spatial patterns of
aridity changes show a shift from arid to the semi-arid (wetter) climate in
annual and Kharif over a large area while showing a shift from arid to hyper-arid
(drier) region during Rabi in a small area. Most of the significant changes
in precipitation and aridity are observed in the years between 1971 and
1980. Overall, aridity is found to increase (drier) in 0.52 %, 4.44 %
and 0.52 % of the area and decrease (wetter) in 11.75 %, 7.57 % and 9.66 % of the
area for annual, Rabi and Kharif seasons respectively during 1967–2016
relative to 1901–1950.
••
TL;DR: In this article, the capability of several lumped hydrological models across Great Britain by focusing on daily flow and peak flow simulations was evaluated using standard performance metrics for daily flows and novel performance metrics considering parameter uncertainty.
Abstract: . Benchmarking model performance across large samples of
catchments is useful to guide model selection and future model development.
Given uncertainties in the observational data we use to drive and evaluate
hydrological models, and uncertainties in the structure and parameterisation
of models we use to produce hydrological simulations and predictions, it is
essential that model evaluation is undertaken within an uncertainty analysis
framework. Here, we benchmark the capability of several lumped hydrological
models across Great Britain by focusing on daily flow and peak flow
simulation. Four hydrological model structures from the Framework for
Understanding Structural Errors (FUSE) were applied to over 1000 catchments
in England, Wales and Scotland. Model performance was then evaluated using
standard performance metrics for daily flows and novel performance metrics
for peak flows considering parameter uncertainty. Our results show that lumped hydrological models were able to produce
adequate simulations across most of Great Britain, with each model producing
simulations exceeding a 0.5 Nash–Sutcliffe efficiency for at least 80 % of
catchments. All four models showed a similar spatial pattern of performance,
producing better simulations in the wetter catchments to the west and poor
model performance in central Scotland and south-eastern England. Poor model performance
was often linked to the catchment water balance, with models unable to
capture the catchment hydrology where the water balance did not close.
Overall, performance was similar between model structures, but different
models performed better for different catchment characteristics and metrics,
as well as for assessing daily or peak flows, leading to the ensemble of
model structures outperforming any single structure, thus demonstrating the
value of using multi-model structures across a large sample of different
catchment behaviours. This research evaluates what conceptual lumped models can achieve as a
performance benchmark and provides interesting insights into where
and why these simple models may fail. The large number of river catchments
included in this study makes it an appropriate benchmark for any future
developments of a national model of Great Britain.
••
TL;DR: In this paper, an ensemble hydrograph separation approach is proposed to estimate the average fraction of new water (e.g., same-day or same-week precipitation) in streamflow across an ensemble of time steps.
Abstract: Decades of hydrograph separation studies have estimated the proportions of
recent precipitation in streamflow using end-member mixing of chemical or
isotopic tracers Here I propose an ensemble approach to hydrograph
separation that uses regressions between tracer fluctuations in precipitation
and discharge to estimate the average fraction of new water (eg, same-day
or same-week precipitation) in streamflow across an ensemble of time steps
The points comprising this ensemble can be selected to isolate conditions of
particular interest, making it possible to study how the new water fraction
varies as a function of catchment and storm characteristics Even when new
water fractions are highly variable over time, one can show mathematically
(and confirm with benchmark tests) that ensemble hydrograph separation will
accurately estimate their average Because ensemble hydrograph separation is
based on correlations between tracer fluctuations rather than on tracer mass
balances, it does not require that the end-member signatures are constant
over time, or that all the end-members are sampled or even known, and it is
relatively unaffected by evaporative isotopic fractionation Ensemble hydrograph separation can also be extended to a multiple regression
that estimates the average (or “marginal”) transit time distribution (TTD)
directly from observational data This approach can estimate both
“backward” transit time distributions (the fraction of streamflow that originated as
rainfall at different lag times) and “forward” transit time distributions
(the fraction of rainfall that will become future streamflow at different
lag times), with and without volume-weighting, up to a user-determined
maximum time lag The approach makes no assumption about the shapes of the
transit time distributions, nor does it assume that they are time-invariant,
and it does not require continuous time series of tracer measurements
Benchmark tests with a nonlinear, nonstationary catchment model confirm that
ensemble hydrograph separation reliably quantifies both new water fractions
and transit time distributions across widely varying catchment behaviors,
using either daily or weekly tracer concentrations as input Numerical
experiments with the benchmark model also illustrate how ensemble hydrograph
separation can be used to quantify the effects of rainfall intensity, flow
regime, and antecedent wetness on new water fractions and transit time
distributions
••
TL;DR: The authors simulated temperature, ice cover, and mixing in four intensively studied German lakes of varying morphology and mixing regime with a one-dimensional lake model and forced the model with an ensemble of 12 RCP4.5 climate projections up to 2100.
Abstract: . The physical response of lakes to climate warming is regionally
variable and highly dependent on individual lake characteristics, making
generalizations about their development difficult. To qualify the role of
individual lake characteristics in their response to regionally homogeneous
warming, we simulated temperature, ice cover, and mixing in four intensively
studied German lakes of varying morphology and mixing regime with a
one-dimensional lake model. We forced the model with an ensemble of 12
climate projections (RCP4.5) up to 2100. The lakes were projected to warm at
0.10–0.11 ∘ C decade −1 , which is 75 %–90 % of the
projected air temperature trend. In simulations, surface temperatures
increased strongly in winter and spring, but little or not at all in summer
and autumn. Mean bottom temperatures were projected to increase in all lakes,
with steeper trends in winter and in shallower lakes. Modelled ice thaw and
summer stratification advanced by 1.5–2.2 and 1.4–1.8 days decade −1 respectively, whereas
autumn turnover and winter freeze timing was less sensitive. The projected
summer mixed-layer depth was unaffected by warming but sensitive to changes
in water transparency. By mid-century, the frequency of ice and
stratification-free winters was projected to increase by about 20 %,
making ice cover rare and shifting the two deeper dimictic lakes to a
predominantly monomictic regime. The polymictic lake was unlikely to become
dimictic by the end of the century. A sensitivity analysis predicted that
decreasing transparency would dampen the effect of warming on mean
temperature but amplify its effect on stratification. However, this
interaction was only predicted to occur in clear lakes, and not in the study
lakes at their historical transparency. Not only lake morphology, but also
mixing regime determines how heat is stored and ultimately how lakes respond
to climate warming. Seasonal differences in climate warming rates are thus
important and require more attention.
••
TL;DR: In this paper, the authors evaluate whether a higher temporal and spatial resolution of rainfall can lead to improved model performance and find that the increase in spatial resolution improves the performance of the model insubstantially or only marginally in most of the study catchments.
Abstract: . Rainfall is the most important input for rainfall–runoff models. It is usually measured at specific sites on a daily or sub-daily timescale and requires interpolation for further application. This study aims to evaluate whether a higher temporal and spatial resolution of rainfall can lead to improved model performance. Four different gridded hourly and daily rainfall datasets with a spatial resolution of 1 km × 1 km for the state of Baden-Wurttemberg in Germany were constructed using a combination of data from a dense network of daily rainfall stations and a less dense network of sub-daily stations. Lumped and spatially distributed HBV models were used to investigate the sensitivity of model performance to the spatial resolution of rainfall. The four different rainfall datasets were used to drive both lumped and distributed HBV models to simulate daily discharges in four catchments. The main findings include
that (1) a higher temporal resolution of rainfall improves the model performance if the station density is high; (2) a combination of observed high temporal resolution observations with disaggregated daily rainfall leads to further improvement in the tested models; and (3) for the present research, the increase in spatial resolution improves the performance of the model insubstantially or only marginally in most of the study catchments.
••
TL;DR: This article used the Weather Research Forecasting (WRF) model at a convection-permitting 4'km resolution to dynamically downscale the mean projection of a 19-member CMIP5 ensemble by the end of the 21st century.
Abstract: . Climate change poses great risks to western Canada's ecosystem and
socioeconomical development. To assess these hydroclimatic risks under high-end emission scenario RCP8.5, this study used the Weather Research
Forecasting (WRF) model at a convection-permitting (CP) 4 km resolution to
dynamically downscale the mean projection of a 19-member CMIP5 ensemble by the
end of the 21st century. The CP simulations include a retrospective simulation (CTL, 2000–2015) for verification forced by ERA-Interim and a pseudo-global warming (PGW) for climate change projection forced with
climate change forcing (2071–2100 to 1976–2005) from CMIP5 ensemble added on ERA-Interim. The retrospective WRF-CTL's surface air temperature simulation was evaluated against Canadian daily analysis ANUSPLIN, showing good agreements in the geographical distribution with cold biases east of the Canadian Rockies, especially in spring. WRF-CTL captures the main pattern of observed precipitation distribution from CaPA and ANUSPLIN but shows a wet bias near the British Columbia coast in winter and over the immediate region on the lee side of the Canadian Rockies. The WRF-PGW simulation shows significant warming relative to CTL, especially over the polar region in the northeast during the cold season, and in daily minimum temperature. Precipitation changes in PGW over CTL vary with the seasons: in spring and late autumn precipitation increases in most areas, whereas in summer in the Saskatchewan River basin and southern Canadian Prairies, the precipitation change is negligible or decreased slightly. With almost no increase in precipitation and much more evapotranspiration in the future, the water availability during the growing season will be challenging for the Canadian Prairies. The WRF-PGW projected warming is less than that by the CMIP5 ensemble in all seasons. The CMIP5 ensemble projects a 10 %–20 % decrease in summer precipitation over the Canadian Prairies and generally agrees with WRF-PGW except for regions with significant terrain. This difference may be due to the much higher resolution of WRF being able to more faithfully represent small-scale summer convection and orographic lifting due to steep terrain. WRF-PGW shows an increase in high-intensity precipitation events and shifts the distribution of precipitation events toward more extremely intensive events in all seasons. Due to this shift in precipitation intensity to the higher end in the PGW simulation, the seemingly moderate increase in the total amount of precipitation in summer east of the Canadian Rockies may underestimate the increase in flooding risk and water shortage for agriculture. The change in the probability distribution of precipitation intensity also calls for innovative bias-correction methods to be developed for the application of the dataset when bias correction is required. High-quality meteorological observation over the region is needed for both forcing high-resolution climate simulation and conducting verification. The high-resolution downscaled climate simulations provide abundant opportunities both for investigating local-scale atmospheric dynamics and for studying climate impacts on hydrology, agriculture, and ecosystems.
••
TL;DR: In this article, the authors proposed a protocol to assess the space-time consistency of 12 satellite-based precipitation products (SPPs) according to various metrics, including direct comparison of SPPs with 72 precipitation gauges; sensitivity of streamflow modelling to SPPs at the outlet of four basins; and sensitivity of distributed snow models using a MODIS snow product as reference in unmonitored mountainous area.
Abstract: . This paper proposes a protocol to assess the space–time consistency of 12
satellite-based precipitation products (SPPs) according to various
indicators, including (i) direct comparison of SPPs with 72 precipitation
gauges; (ii) sensitivity of streamflow modelling to SPPs at the outlet of
four basins; and (iii) the sensitivity of distributed snow models to SPPs
using a MODIS snow product as reference in an unmonitored mountainous area.
The protocol was applied successively to four different time windows
(2000–2004, 2004–2008, 2008–2012 and 2000–2012) to account for the
space–time variability of the SPPs and to a large dataset composed of
12 SPPs (CMORPH–RAW v.1, CMORPH–CRT v.1, CMORPH–BLD v.1, CHIRP v.2, CHIRPS
v.2, GSMaP v.6, MSWEP v.2.1, PERSIANN, PERSIANN–CDR, TMPA–RT v.7, TMPA–Adj
v.7 and SM2Rain–CCI v.2), an unprecedented comparison. The aim of using
different space scales and timescales and indicators was to evaluate whether
the efficiency of SPPs varies with the method of assessment, time window and
location. Results revealed very high discrepancies between SPPs. Compared to
precipitation gauge observations, some SPPs (CMORPH–RAW v.1, CMORPH–CRT
v.1, GSMaP v.6, PERSIANN, and TMPA–RT v.7) are unable to estimate regional
precipitation, whereas the others (CHIRP v.2, CHIRPS v.2, CMORPH–BLD v.1,
MSWEP v.2.1, PERSIANN–CDR, and TMPA–Adj v.7) produce a realistic
representation despite recurrent spatial limitation over regions with
contrasted emissivity, temperature and orography. In 9 out of 10 of the cases
studied, streamflow was more realistically simulated when SPPs were used as
forcing precipitation data rather than precipitation derived from the
available precipitation gauge networks, whereas the SPP's ability to
reproduce the duration of MODIS-based snow cover resulted in poorer
simulations than simulation using available precipitation gauges.
Interestingly, the potential of the SPPs varied significantly when they were
used to reproduce gauge precipitation estimates, streamflow observations or
snow cover duration and depending on the time window considered. SPPs thus
produce space–time errors that cannot be assessed when a single indicator
and/or time window is used, underlining the importance of carefully
considering their space–time consistency before using them for
hydro-climatic studies. Among all the SPPs assessed, MSWEP v.2.1 showed the
highest space–time accuracy and consistency in reproducing gauge
precipitation estimates, streamflow and snow cover duration.
••
TL;DR: In this article, a small Swiss headwater catchment during different wetness and dryness conditions was mapped and the authors estimated their effects on the distribution of travel times to the catchment outlet.
Abstract: . Flowing stream networks dynamically extend and retract, both
seasonally and in response to precipitation events. These network dynamics
can dramatically alter the drainage density and thus the length of
subsurface flow pathways to flowing streams. We mapped flowing stream
networks in a small Swiss headwater catchment during different wetness
conditions and estimated their effects on the distribution of travel times
to the catchment outlet. For each point in the catchment, we determined the
subsurface transport distance to the flowing stream based on the surface
topography and determined the surface transport distance along the flowing
stream to the outlet. We combined the distributions of these travel
distances with assumed surface and subsurface flow velocities to estimate
the distribution of travel times to the outlet. These calculations show that
the extension and retraction of the stream network can substantially change
the mean travel time and the shape of the travel time distribution. During
wet conditions with a fully extended flowing stream network, the travel time
distribution was strongly skewed to short travel times, but as the network
retracted during dry conditions, the distribution of the travel times became
more uniform. Stream network dynamics are widely ignored in catchment
models, but our results show that they need to be taken into account when
modeling solute transport and interpreting travel time distributions.
••
TL;DR: In this paper, a tracer-aided hydrological model was developed to disaggregate the terrain into two dominant landscape units of hillslopes and depression, with fast and slow flow systems.
Abstract: . We developed a new tracer-aided hydrological model that disaggregates cockpit
karst terrain into the two dominant landscape units of hillslopes and
depressions (with fast and slow flow systems). The new model was calibrated
by using high temporal resolution hydrometric and isotope data in the outflow
of Chenqi catchment in Guizhou Province of south-western China. The model
could track hourly water and isotope fluxes through each landscape unit and
estimate the associated storage and water age dynamics. From the model
results we inferred that the fast flow reservoir in the depression had the
smallest water storage and the slow flow reservoir the largest, with the
hillslope intermediate. The estimated mean ages of water draining the
hillslope unit, and the fast and slow flow reservoirs during the study
period, were 137, 326 and 493 days, respectively. Distinct seasonal
variability in hydroclimatic conditions and associated water storage dynamics
(captured by the model) were the main drivers of non-stationary hydrological
connectivity between the hillslope and depression. During the dry season,
slow flow in the depression contributes the largest proportion (78.4 %)
of flow to the underground stream draining the catchment, resulting in weak
hydrological connectivity between the hillslope and depression. During the
wet period, with the resulting rapid increase in storage, the hillslope unit
contributes the largest proportion (57.5 %) of flow to the underground
stream due to the strong hydrological connectivity between the hillslope and
depression. Meanwhile, the tracer-aided model can be used to identify the
sources of uncertainty in the model results. Our analysis showed that the
model uncertainty of the hydrological variables in the different units relies
on their connectivity with the outlet when the calibration target uses only
the outlet information. The model uncertainty was much lower for the
“newer” water from the fast flow system in the depression and flow from the
hillslope unit during the wet season and higher for “older” water from the
slow flow system in the depression. This suggests that to constrain model
parameters further, increased high-resolution hydrometric and tracer data on
the internal dynamics of systems (e.g. groundwater responses during low flow
periods) could be used in calibration.
••
TL;DR: A roadmap for R's future within hydrology is provided, with R packages as a driver of progress in the hydrological sciences, application programming interfaces (APIs) providing new avenues for data acquisition and provision, enhanced teaching of hydrology in R, and the continued growth of the community via short courses and events.
Abstract: . The open-source programming language R has gained a central place in the hydrological sciences over the last decade, driven by the availability of diverse hydro-meteorological data archives and the development of open-source computational tools.
The growth of R's usage in hydrology is reflected in the number of newly published hydrological packages, the strengthening of online user communities, and the popularity of training courses and events.
In this paper, we explore the benefits and advantages of R's usage in hydrology, such as the democratization of data science and numerical literacy, the enhancement of reproducible research and open science, the access to statistical tools, the ease of connecting R to and from other languages, and the support provided by a growing community.
This paper provides an overview of a typical hydrological workflow based on reproducible principles and packages for retrieval of hydro-meteorological data, spatial analysis, hydrological modelling, statistics, and the design of static and dynamic visualizations and documents.
We discuss some of the challenges that arise when using R in hydrology and useful tools to overcome them, including the use of hydrological libraries, documentation, and vignettes (long-form guides that illustrate how to use packages); the role of integrated development environments (IDEs); and the challenges of big data and parallel computing in hydrology.
Lastly, this paper provides a roadmap for R's future within hydrology, with R packages as a driver of progress in the hydrological sciences, application programming interfaces (APIs) providing new avenues for data acquisition and provision, enhanced teaching of hydrology in R, and the continued growth of the community via short courses and events.
••
TL;DR: This work proposes a new approach that exploits existing surveillance camera systems to provide qualitative flood level trend information at scale and uses a deep convolutional neural network to detect floodwater in surveillance footage and a novel qualitative flood index as a proxy for water level fluctuations visible from a surveillance camera's viewpoint.
Abstract: . In many countries, urban flooding due to local,
intense rainfall is expected to become more frequent because of climate
change and urbanization. Cities trying to adapt to this growing risk are
challenged by a chronic lack of surface flooding data that are needed for
flood risk assessment and planning. In this work, we propose a new approach
that exploits existing surveillance camera systems to provide qualitative
flood level trend information at scale. The approach uses a deep
convolutional neural network (DCNN) to detect floodwater in surveillance
footage and a novel qualitative flood index (namely, the static observer flooding index – SOFI) as a proxy for water
level fluctuations visible from a surveillance camera's viewpoint. To
demonstrate the approach, we trained the DCNN on 1218 flooding images
collected from the Internet and applied it to six surveillance videos
representing different flooding and lighting conditions. The SOFI signal
obtained from the videos had a 75 % correlation to the actual
water level fluctuation on average. By retraining the DCNN with a few frames from a
given video, the correlation is increased to 85 % on average. The results
confirm that the approach is versatile, with the potential to be applied to
a variety of surveillance camera models and flooding situations without the
need for on-site camera calibration. Thanks to this flexibility, this
approach could be a cheap and highly scalable alternative to conventional
sensing methods.
••
TL;DR: In this paper, the performance of direct and indirect pedotransfer functions (PTFs) and direct geostatistical mapping methods to derive 3D soil hydraulic properties is analyzed.
Abstract: . Spatial 3-D information on soil hydraulic properties for
areas larger than plot scale is usually derived using indirect methods such
as pedotransfer functions (PTFs) due to the lack of measured information on
them. PTFs describe the relationship between the desired soil hydraulic
parameter and easily available soil properties based on a soil hydraulic
reference dataset. Soil hydraulic properties of a catchment or region can be
calculated by applying PTFs on available soil maps. Our aim was to analyse
the performance of (i) indirect (using PTFs) and (ii) direct
(geostatistical) mapping methods to derive 3-D soil hydraulic properties. The
study was performed on the Balaton catchment area in Hungary, where density
of measured soil hydraulic data fulfils the requirements of geostatistical
methods. Maps of saturated water content (0 cm matric potential), field
capacity ( −330 cm matric potential) and wilting point ( −15 000 cm matric
potential) for 0–30, 30–60 and 60–90 cm soil depth were prepared. PTFs were
derived using the random forest method on the whole Hungarian soil hydraulic
dataset, which includes soil chemical, physical, taxonomical and hydraulic
properties of some 12 000 samples complemented with information on
topography, climate, parent material, vegetation and land use. As a direct and thus geostatistical method, random forest combined with kriging (RFK) was
applied to 359 soil profiles located in the Balaton catchment area. There
were no significant differences between the direct and indirect methods in
six out of nine maps having root-mean-square-error values between 0.052 and
0.074 cm 3 cm −3 , which is in accordance with the internationally
accepted performance of hydraulic PTFs. The PTF-based mapping method
performed significantly better than the RFK for the saturated water content
at 30–60 and 60–90 cm soil depth; in the case of wilting point the RFK
outperformed the PTFs at 60–90 cm depth. Differences between the PTF-based
and RFK mapped values are less than 0.025 cm 3 cm −3 for 65 %–86 %
of the catchment. In RFK, the uncertainty of input environmental covariate
layers is less influential on the mapped values, which is preferable. In the
PTF-based method the uncertainty of mapping soil hydraulic properties is
less computationally intensive. Detailed comparisons of maps derived from the
PTF-based method and the RFK are presented in this paper.
••
TL;DR: In this paper, the authors make a comprehensive summarization of the existing algorithms for generating cloud-free MODIS snow cover products and expose the development trends, including spatial methods, temporal methods, spatio-temporal methods, and multisource fusion methods.
Abstract: . The snow cover products of optical remote sensing systems
play an important role in research into global climate change, the
hydrological cycle, and the energy balance. Moderate Resolution Imaging
Spectroradiometer (MODIS) snow cover products are the most popular datasets
used in the community. However, for MODIS, cloud cover results in spatial
and temporal discontinuity for long-term snow monitoring. In the last few
decades, a large number of cloud removal methods for MODIS snow cover
products have been proposed. In this paper, our goal is to make a
comprehensive summarization of the existing algorithms for generating
cloud-free MODIS snow cover products and to expose the development trends.
The methods of generating cloud-free MODIS snow cover products are
classified into spatial methods, temporal methods, spatio-temporal methods,
and multi-source fusion methods. The spatial methods and temporal methods
remove the cloud cover of the snow product based on the spatial patterns and
temporal changing correlation of the snowpack, respectively. The
spatio-temporal methods utilize the spatial and temporal features of snow
jointly. The multi-source fusion methods utilize the complementary
information among different sources among optical observations, microwave
observations, and station observations.
••
TL;DR: In this paper, the authors discuss the impact of land surface, how it affects shallow and deep clouds, and how these clouds in turn can feed back to the surface by modulating surface radiation and precipitation.
Abstract: . The continental tropics play a leading role in the terrestrial energy,
water, and carbon cycles. Land–atmosphere interactions are integral in the
regulation of these fluxes across multiple spatial and temporal scales over
tropical continents. We review here some of the important characteristics of
tropical continental climates and how land–atmosphere interactions regulate
them. Along with a wide range of climates, the tropics manifest a diverse
array of land–atmosphere interactions. Broadly speaking, in tropical
rainforest climates, light and energy are typically more limiting than
precipitation and water supply for photosynthesis and evapotranspiration (ET),
whereas in savanna and semi-arid climates, water is the critical regulator
of surface fluxes and land–atmosphere interactions. We discuss the impact of
the land surface, how it affects shallow and deep clouds, and how these
clouds in turn can feed back to the surface by modulating surface radiation
and precipitation. Some results from recent research suggest that shallow
clouds may be especially critical to land–atmosphere interactions. On the
other hand, the impact of land-surface conditions on deep convection appears
to occur over larger, nonlocal scales and may be a more relevant
land–atmosphere feedback mechanism in transitional dry-to-wet regions and
climate regimes.