Author
Gemma Coxon
Bio: Gemma Coxon is an academic researcher from University of Bristol. The author has contributed to research in topics: Environmental science & Flood myth. The author has an hindex of 19, co-authored 49 publications receiving 930 citations.
Topics: Environmental science, Flood myth, Streamflow, Groundwater, Rating curve
Papers
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TL;DR: A generalized framework for estimating discharge uncertainty at many gauging stations with different errors in the stage‐discharge relationship is presented and is shown to be robust, versatile and able to capture place‐specific uncertainties for a number of different examples.
Abstract: A generalized framework for discharge uncertainty estimation is presentedAllows estimation of place-specific discharge uncertainties for many catchmentsLocal conditions dominate in determining discharge uncertainty magnitudes.
162 citations
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TL;DR: In this article, the authors report a new and significantly enhanced analysis of US flood hazard at 30m spatial resolution, which includes updated hydrography data, new methods to determine channel d...
Abstract: This paper reports a new and significantly enhanced analysis of US flood hazard at 30m spatial resolution. Specific improvements include updated hydrography data, new methods to determine channel d...
123 citations
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TL;DR: In this paper, the authors quantified signature uncertainty stemming from discharge data uncertainty for 43 UK catchments and propagated these uncertainties in signature regionalization, while accounting for regionalization uncertainty with a weighted-pooling-group approach.
Abstract: Reliable information about hydrological behavior is needed for water-resource management and scientific investigations. Hydrological signatures quantify catchment behavior as index values, and can be predicted for ungauged catchments using a regionalization procedure. The prediction reliability is affected by data uncertainties for the gauged catchments used in prediction and by uncertainties in the regionalization procedure. We quantified signature uncertainty stemming from discharge data uncertainty for 43 UK catchments and propagated these uncertainties in signature regionalization, while accounting for regionalization uncertainty with a weighted-pooling-group approach. Discharge uncertainty was estimated using Monte Carlo sampling of multiple feasible rating curves. For each sampled rating curve, a discharge time series was calculated and used in deriving the gauged signature uncertainty distribution. We found that the gauged uncertainty varied with signature type, local measurement conditions and catchment behavior, with the highest uncertainties (median relative uncertainty ±30–40% across all catchments) for signatures measuring high- and low-flow magnitude and dynamics. Our regionalization method allowed assessing the role and relative magnitudes of the gauged and regionalized uncertainty sources in shaping the signature uncertainty distributions predicted for catchments treated as ungauged. We found that 1) if the gauged uncertainties were neglected there was a clear risk of over-conditioning the regionalization inference, e.g. by attributing catchment differences resulting from gauged uncertainty to differences in catchment behavior, and 2) uncertainty in the regionalization results was lower for signatures measuring flow distribution (e.g. mean flow) than flow dynamics (e.g. autocorrelation), and for average flows (and then high flows) compared to low flows. This article is protected by copyright. All rights reserved.
115 citations
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TL;DR: In this article, the authors compared uncertainty estimates and stage-discharge rating curves from seven methods at three different locations of varying hydraulic complexity and found that fullwidth 95% uncertainties for the different methods ranged from 3 to 17% for median flows.
Abstract: Streamflow time series are commonly derived from stage-discharge rating curves, but theuncertainty of the rating curve and resulting streamflow series are poorly understood. While differentmethods to quantify uncertainty in the stage-discharge relationship exist, there is limited understanding ofhow uncertainty estimates differ between methods due to different assumptions and methodologicalchoices. We compared uncertainty estimates and stage-discharge rating curves from seven methods at threeriver locations of varying hydraulic complexity. Comparison of the estimated uncertainties revealed a widerange of estimates, particularly for high and low flows. At the simplest site on the Isere River (France), fullwidth 95% uncertainties for the different methods ranged from 3 to 17% for median flows. In contrast,uncertainties were much higher and ranged from 41 to 200% for high flows in an extrapolated section of therating curve at the Mahurangi River (New Zealand) and 28 to 101% for low flows at the Taf River (UnitedKingdom), where the hydraulic control is unstable at low flows. Differences between methods result fromdifferences in the sources of uncertainty considered, differences in the handling of the time-varying nature ofrating curves, differences in the extent of hydraulic knowledge assumed, and differences in assumptionswhen extrapolating rating curves above or below the observed gaugings. Ultimately, the selection of anuncertainty method requires a match between user requirements and the assumptions made by theuncertainty method. Given the signi ficant differences in uncertainty estimates between methods, we suggestthat a clear statement of uncertainty assumptions be presented alongside streamflow uncertainty estimates.
110 citations
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TL;DR: Coxon et al. as discussed by the authors presented the first large-sample catchment hydrology dataset for Great Britain, CAMELS-GB (Catchment Attributes and MEteorology for Large-sampleStudies).
Abstract: . We present the first large-sample catchment hydrology dataset for Great
Britain, CAMELS-GB (Catchment Attributes and MEteorology for Large-sample
Studies). CAMELS-GB collates river flows, catchment attributes and catchment
boundaries from the UK National River Flow Archive together with a suite of
new meteorological time series and catchment attributes. These data are
provided for 671 catchments that cover a wide range of climatic,
hydrological, landscape, and human management characteristics across Great
Britain. Daily time series covering 1970–2015 (a period including several
hydrological extreme events) are provided for a range of
hydro-meteorological variables including rainfall, potential
evapotranspiration, temperature, radiation, humidity, and river flow. A
comprehensive set of catchment attributes is quantified including
topography, climate, hydrology, land cover, soils, and hydrogeology.
Importantly, we also derive human management attributes (including
attributes summarising abstractions, returns, and reservoir capacity in each
catchment), as well as attributes describing the quality of the flow data
including the first set of discharge uncertainty estimates (provided at
multiple flow quantiles) for Great Britain. CAMELS-GB (Coxon et al., 2020;
available at https://doi.org/10.5285/8344e4f3-d2ea-44f5-8afa-86d2987543a9 )
is intended for the community as a publicly available, easily accessible
dataset to use in a wide range of environmental and modelling analyses.
84 citations
Cited by
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11 Dec 20121,704 citations
25 Apr 2017
TL;DR: This presentation is a case study taken from the travel and holiday industry and describes the effectiveness of various techniques as well as the performance of Python-based libraries such as Python Data Analysis Library (Pandas), and Scikit-learn (built on NumPy, SciPy and matplotlib).
Abstract: This presentation is a case study taken from the travel and holiday industry. Paxport/Multicom, based in UK and Sweden, have recently adopted a recommendation system for holiday accommodation bookings. Machine learning techniques such as Collaborative Filtering have been applied using Python (3.5.1), with Jupyter (4.0.6) as the main framework. Data scale and sparsity present significant challenges in the case study, and so the effectiveness of various techniques are described as well as the performance of Python-based libraries such as Python Data Analysis Library (Pandas), and Scikit-learn (built on NumPy, SciPy and matplotlib). The presentation is suitable for all levels of programmers.
1,338 citations
01 Dec 2012
Abstract: We upscaled FLUXNET observations of carbon dioxide, water, and energy fluxes to the global scale using the machine learning technique, model tree ensembles (MTE). We trained MTE to predict site-level gross primary productivity (GPP), terrestrial ecosystem respiration (TER), net ecosystem exchange (NEE), latent energy (LE), and sensible heat (H) based on remote sensing indices, climate and meteorological data, and information on land use. We applied the trained MTEs to generate global flux fields at a 0.5 degrees x 0.5 degrees spatial resolution and a monthly temporal resolution from 1982 to 2008. Cross-validation analyses revealed good performance of MTE in predicting among-site flux variability with modeling efficiencies (MEf) between 0.64 and 0.84, except for NEE (MEf = 0.32). Performance was also good for predicting seasonal patterns (MEf between 0.84 and 0.89, except for NEE (0.64)). By comparison, predictions of monthly anomalies were not as strong (MEf between 0.29 and 0.52). Improved accounting of disturbance and lagged environmental effects, along with improved characterization of errors in the training data set, would contribute most to further reducing uncertainties. Our global estimates of LE (158 +/- 7 J x 10(18) yr(-1)), H (164 +/- 15 J x 10(18) yr(-1)), and GPP (119 +/- 6 Pg C yr(-1)) were similar to independent estimates. Our global TER estimate (96 +/- 6 Pg C yr(-1)) was likely underestimated by 5-10%. Hot spot regions of interannual variability in carbon fluxes occurred in semiarid to semihumid regions and were controlled by moisture supply. Overall, GPP was more important to interannual variability in NEE than TER. Our empirically derived fluxes may be used for calibration and evaluation of land surface process models and for exploratory and diagnostic assessments of the biosphere.
948 citations
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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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Oeschger Centre for Climate Change Research1, University of Bern2, University of Adelaide3, University of Reading4, Columbia University5, California Institute of Technology6, Lamont–Doherty Earth Observatory7, VU University Amsterdam8, University of California, Irvine9, École des ponts ParisTech10, École Normale Supérieure11, Leipzig University12, Max Planck Society13, University of Graz14, University of Lisbon15, University of New South Wales16, Vrije Universiteit Brussel17, University of Geneva18
TL;DR: A typology of compound events is proposed, distinguishing events that are preconditioned, multivariate, temporally compounding and spatially compounding, and suggests analytical and modelling approaches to aid in their investigation.
Abstract: Compound weather and climate events describe combinations of multiple climate drivers and/or hazards that contribute to societal or environmental risk. Although many climate-related disasters are caused by compound events, the understanding, analysis, quantification and prediction of such events is still in its infancy. In this Review, we propose a typology of compound events and suggest analytical and modelling approaches to aid in their investigation. We organize the highly diverse compound event types according to four themes: preconditioned, where a weather-driven or climate-driven precondition aggravates the impacts of a hazard; multivariate, where multiple drivers and/or hazards lead to an impact; temporally compounding, where a succession of hazards leads to an impact; and spatially compounding, where hazards in multiple connected locations cause an aggregated impact. Through structuring compound events and their respective analysis tools, the typology offers an opportunity for deeper insight into their mechanisms and impacts, benefiting the development of effective adaptation strategies. However, the complex nature of compound events results in some cases inevitably fitting into more than one class, necessitating soft boundaries within the typology. Future work must homogenize the available analytical approaches into a robust toolset for compound-event analysis under present and future climate conditions. Research on compound events has increased vastly in the last several years, yet, a typology was absent. This Review proposes a comprehensive classification scheme, incorporating compound events that are preconditioned, multivariate, temporally compounding and spatially compounding events.
455 citations