Showing papers on "Water cycle published in 2003"
TL;DR: A comparison of salinities on a long transect through the western basins of the Atlantic Ocean between the 1950s and the 1990s is presented, suggesting shifts in the oceanic distribution of fresh and saline waters are occurring worldwide in ways that suggest links to global warming and possible changes in the hydrologic cycle of the Earth.
Abstract: The oceans are a global reservoir and redistribution agent for several important constituents of the Earth's climate system, among them heat, fresh water and carbon dioxide. Whereas these constituents are actively exchanged with the atmosphere, salt is a component that is approximately conserved in the ocean. The distribution of salinity in the ocean is widely measured, and can therefore be used to diagnose rates of surface freshwater fluxes, freshwater transport and local ocean mixing--important components of climate dynamics. Here we present a comparison of salinities on a long transect (50 degrees S to 60 degrees N) through the western basins of the Atlantic Ocean between the 1950s and the 1990s. We find systematic freshening at both poleward ends contrasted with large increases of salinity pervading the upper water column at low latitudes. Our results extend a growing body of evidence indicating that shifts in the oceanic distribution of fresh and saline waters are occurring worldwide in ways that suggest links to global warming and possible changes in the hydrologic cycle of the Earth.
517 citations
TL;DR: In this paper, it is argued that the diurnal cycle over the islands and the complex circulation patterns generated by land-sea contrasts are crucial for the energy and hydrological cycles of the Maritime Continent and for determining the mean climate.
Abstract: The Maritime Continent, with its complex system of islands and shallow seas, presents a major challenge to models, which tend to systematically underestimate the precipitation in this region. Experiments with a climate version of the Met Office model (HadAM3) show that even with a threefold increase in horizontal resolution there is no improvement in the dry bias. It is argued that the diurnal cycle over the islands and the complex circulation patterns generated by land–sea contrasts are crucial for the energy and hydrological cycles of the Maritime Continent and for determining the mean climate. It is shown that the model has substantial errors in its simulation of the diurnal cycle over the islands, which can rectify onto the seasonal mean climate. It is further argued that deficient rainfall over the Maritime Continent could be a driver for other systematic errors, such as the excess precipitation over the western Indian Ocean. To demonstrate the sensitivity of global systematic model errors t...
409 citations
TL;DR: In this paper, the authors describe an approach in which ecological concepts from a global vegetation dynamics model are added to the land component of a climate model to grow plants interactively to simulate global biogeography, net primary production and dynamics of tundra, boreal forest, northern hardwood forest, tropical rainforest, and savanna ecosystems.
Abstract: Changes in vegetation structure and biogeography due to climate change feedback to alter climate by changing fluxes of energy, moisture, and momentum between land and atmosphere. While the current class of land process models used with climate models parameterizes these fluxes in detail, these models prescribe surface vegetation and leaf area from data sets. In this paper, we describe an approach in which ecological concepts from a global vegetation dynamics model are added to the land component of a climate model to grow plants interactively. The vegetation dynamics model is the Lund–Potsdam–Jena (LPJ) dynamic global vegetation model. The land model is the National Center for Atmospheric Research (NCAR) Land Surface Model (LSM). Vegetation is defined in terms of plant functional types. Each plant functional type is represented by an individual plant with the average biomass, crown area, height, and stem diameter (trees only) of its population, by the number of individuals in the population, and by the fractional cover in the grid cell. Three time-scales (minutes, days, and years) govern the processes. Energy fluxes, the hydrologic cycle, and carbon assimilation, core processes in LSM, occur at a 20 min time step. Instantaneous net assimilated carbon is accumulated annually to update vegetation once a year. This is carried out with the addition of establishment, resource competition, growth, mortality, and fire parameterizations from LPJ. The leaf area index is updated daily based on prevailing environmental conditions, but the maximum value depends on the annual vegetation dynamics. The coupling approach is successful. The model simulates global biogeography, net primary production, and dynamics of tundra, boreal forest, northern hardwood forest, tropical rainforest, and savanna ecosystems, which are consistent with observations. This suggests that the model can be used with a climate model to study biogeophysical feedbacks in the climate system related to vegetation dynamics.
378 citations
TL;DR: In this paper, the authors assess the impact of changes in the sediment flux to the coastal zone because of the conflicting impacts of humans on the hydrological cycle and find that sediment is dispersed over smaller areas of the continental margin, resulting in an accelerated coastal erosion and a decrease in habitat.
259 citations
TL;DR: In this paper, the authors take a regional approach, using case studies to assess and compare the hydrological significance of mountains in the Rhine River catchment and 19 additional selected catchments worldwide, with the river Euphrates serving as an example.
Abstract: Mountains and highlands are often called the world's natural “water towers” because they provide essential freshwater for populations both upstream and downstream. Despite this, knowledge about the significance of mountains in the hydrological cycle is still uncertain. The present article takes a regional approach, using case studies to assess and compare the hydrological significance of mountains. Methods are developed based on the experience gained in the Rhine River catchment and then applied to 19 additional selected catchments worldwide, with the river Euphrates serving as an example. The resulting comparative assessment serves as an elaboration on the hydrological significance of the world's mountains and underscores their function as sources of large, reliable, and compensatory discharge. The mean annual mountain contribution to total discharge in the river basins included in our case studies is disproportionately high, at 63%, with a mean relative mountain area of only 32%. Furthermore, d...
231 citations
TL;DR: Water reuse increases the available supply of water and enables human needs to be met with less fresh water as discussed by the authors, and water reuse case studies in agriculture, urban areas, industry and water resource supplementation in Australia and other countries.
Abstract: The world's supply of fresh water is finite and is threatened by pollution. Rising demands for water to supply agriculture, industry and cities are leading to competition over the allocation of limited fresh water resources. This paper examines how water reuse increases the available supply of water and enables human needs to be met with less fresh water. The paper is illustrated with water reuse case studies in agriculture, urban areas, industry and water resource supplementation in Australia and other countries. The links between water reuse and sustainable water management are examined. Water conservation and water reuse produce substantial environmental benefits, arising from reductions in water diversions, and reductions in the impacts of wastewater discharges on environmental water quality. Some examples are presented demonstrating the environmental benefits in quantitative terms. The paper also describes the economic and environmental benefits identified in a number of recent integrated water cycle planning studies in Australia.
215 citations
TL;DR: In this paper, an improved version of the Arno scheme was developed for application in global and regional climate models, where surface runoff is computed as infiltration excess from a "bucket" type reservoir which takes the subgrid variability of soil saturation within a model gridbox into account.
Abstract: In this study it is shown that the availability of a very high resolution dataset of land surface characteristics leads to the improvement of a surface runoff parameterization scheme. The improved parameterization scheme was developed for application in global and regional climate models and is a further development of the Arno scheme that is widely used in climate models. Here, surface runoff is computed as infiltration excess from a "bucket" type reservoir which takes the subgrid variability of soil saturation within a model gridbox into account. Instead of prescribing a distribution of subgrid scale soil water capacities as in the original Arno scheme, the array of high resolution soil water capacities taken from a global 1 km dataset of land surface parameters is used to obtain individual fractional saturation curves for each model gridbox. From each saturation curve, the three parameters (a shape parameter describing the shape of the subgrid distribution of soil water capacities, subgrid minimum and maximum soil water capacity) required in the modified formulation of the scheme are derived via optimization. As in the original Arno scheme applied in the ECHAM general circulation model and the REMO regional climate model, topography variations will influence the distribution of saturated subgrid areas within a model gridbox. At most gridboxes the net effect of these changes is such that more runoff is produced for high soil water contents and less runoff for low soil water contents. A validation of simulated discharge computed with a simplified land surface scheme applied to reanalysis data of the European Centre for Medium-Range Weather Forecasts and a hydrological discharge model has shown that these changes lead to a more realistic simulation of the annual cycle of discharge for several catchments. In particular this could be shown for the Yangtze Kiang and Amur catchments where adequate input data are available.
201 citations
TL;DR: The impacts of climate change on the agricultural water cycle and their implications for agricultural production in the 2020s were assessed by water-balance calculations for Chinese croplands by identifying rain-fed crops in the north China plain and northeast China would face water-related challenges in coming decades.
188 citations
Abstract: The evaluation of the quality and usefulness of climate modeling systems is dependent upon an assessment of both the limited predictability of the climate system and the uncertainties stemming from model formulation. In this study a methodology is presented that is suited to assess the performance of a regional climate model (RCM), based on its ability to represent the natural interannual variability on monthly and seasonal timescales. The methodology involves carrying out multiyear ensemble simulations (to assess the predictability bounds within which the model can be evaluated against observations) and multiyear sensitivity experiments using different model formulations (to assess the model uncertainty). As an example application, experiments driven by assimilated lateral boundary conditions and sea surface temperatures from the ECMWF Reanalysis Project (ERA-15, 1979–1993) were conducted. While the ensemble experiment demonstrates that the predictability of the regional climate varies strongly between different seasons and regions, being weakest during the summer and over continental regions, important sensitivities of the modeling system to parameterization choices are uncovered. In particular, compensating mechanisms related to the long-term representation of the water cycle are revealed, in which summer dry and hot conditions at the surface, resulting from insufficient evaporation, can persist despite insufficient net solar radiation (a result of unrealistic cloud-radiative feedbacks).
180 citations
TL;DR: In this article, the authors used simulations of terrestrial water budgets and simulations of the climate of the twenty-first century using the parallel climate model to estimate the time required to detect plausible changes in precipitation (P), evaporation (E), and discharge (Q) if the global water cycle intensifies in response to global warming.
Abstract: Diagnostic studies of offline, global-scale Variable Infiltration Capacity (VIC) model simulations of terrestrial water budgets and simulations of the climate of the twenty-first century using the parallel climate model (PCM) are used to estimate the time required to detect plausible changes in precipitation ( P), evaporation (E), and discharge (Q) if the global water cycle intensifies in response to global warming. Given the annual variability in these continental hydrological cycle components, several decades to perhaps more than a century of observations are needed to detect water cycle changes on the order of magnitude predicted by many global climate model studies simulating global warming scenarios. Global increases in precipitation, evaporation, and runoff of 0.6, 0.4, and 0.2 mm yr21 require approximately 30‐45, 25‐35, and 50‐60 yr, respectively, to detect with high confidence. These conservative detection time estimates are based on statistical error criteria (a 5 0.05, b 5 0.10) that are associated with high statistical confidence, 1 2 a (accept hypothesis of intensification when true, i.e., intensification is occurring), and high statistical power, 1 2 b (reject hypothesis of intensification when false, i.e., intensification is not occurring). If one is willing to accept a higher degree of risk in making a statistical error, the detection time estimates can be reduced substantially. Owing in part to greater variability, detection time of changes in continental P, E, and Q are longer than those for the globe. Similar calculations performed for three Global Energy and Water Experiment (GEWEX) basins reveal that minimum detection time for some of these basins may be longer than that for the corresponding continent as a whole, thereby calling into question the appropriateness of using continental-scale basins alone for rapid detection of changes in continental water cycles. A case is made for implementing networks of small-scale indicator basins, which collectively mimic the variability in continental P, E, and Q, to detect acceleration in the global water cycle.
176 citations
TL;DR: In this article, the concept of virtual water and potential use of this water as a global solution to regional deficits is discussed. And the authors propose four pillars of integrated agricultural water management and their suitable combinations will be the key to future agricultural and economic growth and social wealth, particularly in regions that are deficient in freshwater supplies.
TL;DR: In this article, the vulnerability of water resources in the conterminous US to climate changes in 10-year periods centered on 2030 and 2095 as projected by the Hadley/United Kingdom Meteorological Office (UKMO) general circulation model (GCM; HadCM2) were modeled using the Hydrologic Unit Model for the United States (HUMUS), a biophysically based hydrology model consisting of a Geographical information system (GIS) that provides data on soils, land use and climate to drive the Soil Water Assessment Tool (SWAT).
TL;DR: In this paper, a new water isotope circulation model on a global scale that includes a Rayleigh equation and the use of external meteorological forcings is developed, which highlights the importance of transport and mixing of air masses with different isotopic concentrations.
Abstract: [1] Stable water isotopes (D and 18O) in precipitation have large spatial and temporal variability and are used widely to trace the global hydrologic cycle. The two models that have been used in the past to examine the variability of precipitation isotopes are Rayleigh-type models and isotope-atmospheric general circulation models. The causes of short-term (1–10 day) variability in precipitation isotopes, however, remain unclear. This study seeks to explain isotope variability quantitatively at such scale. A new water isotope circulation model on a global scale that includes a Rayleigh equation and the use of external meteorological forcings is developed. Transport and mixing processes of water masses and isotopes that have been neglected in earlier Rayleigh models are included in the new model. A simulation of 18O for 1998 is forced with data from the Global Energy and Water Cycle Experiment (GEWEX) Asian Monsoon Experiments (GAME) reanalysis. The results are validated by Global Network of Isotopes in Precipitation (GNIP) monthly observations with correlation R = 0.76 and a significance level >99% and by daily observations at three sites in Thailand with similar correlation and significance. A quantitative analysis of the results shows that among three factors that cause isotopic variability, the contribution of moisture flux is the largest, accounting for 37% at Chiangmai, and 46% globally. This highlights the importance of transport and mixing of air masses with different isotopic concentrations. A sensitivity analysis of the temporal and spatial resolution required for each variable is also made, and the model is applied to two additional data sets. The more accurate Global Precipitation Climatology Project (GPCP) precipitation data set yields improved model results at all three observation sites in Thailand. The National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis allows the simulation to cover 2 years, reproducing reasonable interannual isotopic variability.
TL;DR: In this article, it is demonstrated that while both the radiative heating by increasing CO2 and the resulting higher sea surface temperatures contribute to warm the atmosphere, they act against each other in changing the hydrological cycle.
Abstract: The fact that the surface and tropospheric temperatures increase with increasing CO2 has been well documented by numerical model simulations; however, less agreement is found for the changes in the intensity of precipitation and the hydrological cycle. Here, it is demonstrated that while both the radiative heating by increasing CO2 and the resulting higher sea surface temperatures contribute to warm the atmosphere, they act against each other in changing the hydrological cycle. As a consequence, in a warmer climate forced by increasing CO2 the intensity of the hydrological cycle can be either more or less intense depending upon the degree of surface warming.
TL;DR: In this paper, the systematic biases in temperature and precipitation, and the surface water budget of European Centre for Medium-Range Weather Forecasts (ECMWF) 40-yr reanalysis (ERA-40) for the Mackenzie River basin are assessed by comparing monthly averages from ERA-40 with basin averages of surface observations of temperature, precipitation, evaporation, and streamflow.
Abstract: The systematic biases in temperature and precipitation, and the surface water budget of European Centre for Medium-Range Weather Forecasts (ECMWF) 40-yr reanalysis (ERA-40) for the Mackenzie River basin are assessed by comparing monthly averages from ERA-40 with basin averages of surface observations of temperature, precipitation, evaporation, and streamflow from the Mackenzie Global Energy and Water Cycle Experiment (GEWEX) Study (MAGS). The bias and spinup of precipitation in ERA-40 changes significantly over the analysis period. On an annual basis, both precipitation bias and spinup are correlated with the analysis increment of atmospheric total column water vapor. ERA-40 has, in addition, a high bias of precipitation in spring and a low bias in fall. The monthly precipitation analysis is best for the most recent decade, when the bias of the 0–12-h forecast precipitation is only a few percent higher than the MAGS observations, and ERA-40 represents rather well the variability of monthly precip...
TL;DR: The Swiss National Network for the Observation of Isotopes in the Water Cycle (NISOT) includes eleven precipitation, seven surface water (river) and three groundwater stations, where tritium, deuterium and oxygen-18 are monthly measured in composite samples.
Abstract: The Swiss National Network for the Observation of Isotopes in the Water Cycle (NISOT) includes eleven precipitation, seven surface water (river) and three groundwater stations, where tritium, deuterium and oxygen-18 are monthly measured in composite samples. The network provides a good overview of the characteristic isotope signatures in recharge waters in Switzerland and of the relations between isotopes and altitude, orography and the amount of precipitation. Mixing of air water vapour and surface waters can be observed along a NW/SE cross section through the Alps. With increasing length of the data series, the network provides a valuable contribution for national and international scientific and practical applications in surface and subsurface hydrology, climatology and biology. The Swiss Geological Survey at the Federal Office for Water and Geology operates the isotope network within the legal framework of the Federal Law on the Protection of Waters and guarantees quality, access and distribution of the isotope data.
University of California, San Diego1, National Oceanic and Atmospheric Administration2, University of Maryland, College Park3, University of New Hampshire4, University of Georgia5, University of Iowa6, University of South Carolina7, University of Delaware8, University of Washington9, Rutgers University10, Pennsylvania State University11, Princeton University12, United States Geological Survey13, Colorado State University14, University Corporation for Atmospheric Research15
TL;DR: In this article, a preliminary water and energy budget synthesis (WEBS) was developed for the period 1996-1999 from the best available observations and models, which included a representative global general circulation model, regional climate model, and a macro-scale hydrologic model as well as a global reanalysis and a regional analysis.
Abstract: [1] As part of the World Climate Research Program's (WCRPs) Global Energy and Water-Cycle Experiment (GEWEX) Continental-scale International Project (GCIP), a preliminary water and energy budget synthesis (WEBS) was developed for the period 1996–1999 from the “best available” observations and models. Besides this summary paper, a companion CD-ROM with more extensive discussion, figures, tables, and raw data is available to the interested researcher from the GEWEX project office, the GAPP project office, or the first author. An updated online version of the CD-ROM is also available at http://ecpc.ucsd.edu/gcip/webs.htm/. Observations cannot adequately characterize or “close” budgets since too many fundamental processes are missing. Models that properly represent the many complicated atmospheric and near-surface interactions are also required. This preliminary synthesis therefore included a representative global general circulation model, regional climate model, and a macroscale hydrologic model as well as a global reanalysis and a regional analysis. By the qualitative agreement among the models and available observations, it did appear that we now qualitatively understand water and energy budgets of the Mississippi River Basin. However, there is still much quantitative uncertainty. In that regard, there did appear to be a clear advantage to using a regional analysis over a global analysis or a regional simulation over a global simulation to describe the Mississippi River Basin water and energy budgets. There also appeared to be some advantage to using a macroscale hydrologic model for at least the surface water budgets.
TL;DR: In this article, the sensitivity of the modeled evaporation and precipitation to the vegetation leaf area index (LAI) was investigated with the global model of the European Centre for Medium-Range Weather Forecasts (ECMWF).
Abstract: [1] Numerical experiments with the global model of the European Centre for Medium-Range Weather Forecasts (ECMWF) were devoted to the sensitivity of the modeled evaporation and precipitation to the vegetation leaf area index (LAI). The temporally static LAI distribution was replaced with a seasonally varying LAI, derived from normalized difference vegetation index (NDVI) archives. The seasonality of surface evaporation increased likewise, in combination with a response of increased precipitation seasonality over land. In a second set of experiments, the LAI estimates were perturbed by a noise term reflecting measurement accuracy and interannual variability. The resulting noise in evaporation and precipitation was compared to the noise intrinsically generated by the atmosphere. For periods and areas where evaporation forms a large term in the surface energy balance, the noise added to the LAI could be clearly discerned from the atmospheric noise, indicating that improved LAI estimation techniques can have a detectable impact on the surface evaporation calculated in the ECMWF global model.
TL;DR: In this article, the effects of permafrost on hydrological processes in the cryosphere were examined and recorded in the ground surface layer of the eastern Tibetan Plateau, and the results showed that coupling of the thaw-frost cycle to seasonality in precipitation is the principal control of hydrologogical processes of the upper 2 m of the soil.
01 Feb 2003
TL;DR: In this paper, a coupled sea ice-ocean Baltic Sea model was used to model salinity and temperature in the Gulf of Bothnia, Gulf of Finland, and Gulf of Riga.
Abstract: The modeling of salinity and temperature in Gulf of Bothnia, Gulf of Finland, and Gulf of Riga is investigated by using a coupled sea ice-ocean Baltic Sea model. 18 years, from late 1980 to the end of 1998, have been investigated. The forcing data extracted taken from a gridded meteorological data base, sea level data from the Kattegat, and river runoff data to the different subbasins of the Baltic Sea from a hydrological data base. To improve the gridded meteorological data base a statistical model for the reduction of geostrophic winds to surface winds was developed. In the analysis it was shown that the calculated long-term salinity and temperature structures were stable and in good agreement with observations. This was made possible by using three different strait-flow models connecting the subbasins of the Baltic Sea. The seasonal and interannual variations of temperature and salinity were also well simulated by the model, implying that the coupling between the atmosphere and the Baltic Sea as well as the diapycnal mixing are reasonably well understood. The water cycle and the surface heat balance were calculated using the 18-year simulation. In the water-balance calculations it was shown that the volume flows from the large gulfs of the Baltic Sea were mainly due to baroclinic transports and that net precipitation added freshwater during the studied period, particularly to the large gulfs. From the heat-balance calculation it is concluded that the Baltic Sea is almost in local balance with the atmosphere. The Bothnian Bay, Gulf of Finland and Gulf of Riga loose heat, whereas the Bothnian Sea gains heat, calculated as long-term means.
TL;DR: In this article, a series of numerical experiments have been designed to understand the physics at the soil-vegetation-snow-atmosphere interface and to find the major parameterizations/ parameters, which are crucial to simulate cold season processes.
Abstract: [1] A series of numerical experiments have been designed to understand the physics at the soil-vegetation-snow-atmosphere interface and to find the major parameterizations/ parameters, which are crucial to simulate cold season processes. Observational data sets from Col de Porte of France, Ovre Lansjarv of Sweden, and Gander of Canada were used to help interpret the results. This study shows that snow layering and compaction are among the most important factors affecting proper simulations of snow depth, snow water equivalent (SWE), surface temperature, and surface runoff. Fixed snow density could produce as high as 100 percent error in estimating snow depth and could cause significant biases in SWE simulation during the melting period. Furthermore, with a bulk snow/soil layer, the simulated surface temperature would persistently be close to the freezing point with substantially hampered variability, and the variability and the amplitude of the runoff during the snow-melting season could also be severely underestimated. The experiments also show that proper snow albedo is crucial during the ablation period and affects the magnitude and timing in both SWE and runoff simulations. Furthermore, this study indicates that the parameterizations in the surface aerodynamic resistance in the stable regime play an important role in determining the sensible and latent heat fluxes during the winter season in the Arctic region and then affect the snow depth simulations and prediction of snow melting as well as runoff timing. Although the snow may fully cover the ground in cold regions during the winter, numerical experiments in this study show the vegetation still exerts a substantial influence in the snow depth and runoff simulations. Numerical experimentation shows that less downward sensible heat on the bare ground produces thick snow cover and extremely high peak runoff, which leads to a typical deforestation scenario in cold regions. INDEX TERMS: 0315 Atmospheric Composition and Structure: Biosphere/atmosphere interactions; 1655 Global Change: Water cycles (1836); 1860 Hydrology: Runoff and streamflow; 1863 Hydrology: Snow and ice (1827); KEYWORDS: snow parameterization, simulation of snow and runoff
01 Jan 2003
TL;DR: In this article, the authors present a list of scientific and common species names for carbon cycle processes, including water cycle processes and carbon decomposition and soil carbon turnover, as well as the response of other organisms.
Abstract: Foreword * Preface * Introduction * Carbon Cycle Processes * Water Cycle Processes* Decomposition and Soil Carbon Turnover * Plant Growth and Mortality * Response of Other Organisms * Forest Stand-Level Syntheses * Extrapolations * Appendix: List of Scientific and Common Species Names
TL;DR: In this article, a large amount of data has been collected, which is the best data set so far for the study of energy and water cycle over the Tibetan Plateau, and some results on the local surface energy partitioning (imbalance, diurnal variation, inter-monthly variation and inter-yearly variation etc.) are presented by using the field observational data in this study.
Abstract: The energy and water cycle over the Tibetan Plateau play an important role in the Asian monsoon system, which in turn is a major component of both the energy and water cycles of the global climate system. The intensive observation period and long-term observation of the GEWEX (global energy and water cycle experiment) Asian monsoon experiment on the Tibetan Plateau (GAME/Tibet) and CEOP (coordinated enhanced observing period) Asia–Australia monsoon project (CAMP) on the Tibetan Plateau (CAMP/Tibet) have been done successfully in the past five years. A large amount of data has been collected, which is the best data set so far for the study of energy and water cycle over the Tibetan Plateau. The field experiments of GAME/Tibet and CAMP/Tibet are introduced and some results on the local surface energy partitioning (imbalance, diurnal variation, inter-monthly variation and inter-yearly variation etc.) are presented by using the field observational data in this study. The study on the regional surface energy partitioning is of paramount importance over heterogeneous landscape of the Tibetan Plateau and it is also one of the main scientific objectives of GAME/Tibet and CAMP/Tibet. Therefore, the regional distributions of surface variables (surface reflectance and surface temperature), vegetation variables (NDVI, MSAVI, vegetation coverage and LAI) and surface heat fluxes (net radiation flux, soil heat flux, sensible and latent heat flux) are also derived by combining NOAA-14 AVHRR data with field observations in this study.
TL;DR: In this article, a large-scale runoff routing model (RiTHM) was developed to simulate the discharge of large rivers from the total runoff simulated by the LMD GCM.
TL;DR: In this article, a physically based rainfall-runoff model is developed for a typical, 1.9-km2 endoreic system named Wankama, which is monitored continuously since 1992.
TL;DR: In this paper, the authors examined large-scale aspects of the global freshwater budget in a simulation, of over 1000 years, by the Hadley Centre coupled climate model (HadCM3), with the major change being a relative increase of freshwater transport from the Southern Ocean into the Atlantic Ocean.
Abstract: The hydrological cycle can influence climate through a great variety of processes. A good representation of the hydrological cycle in climate models is therefore crucial. Attempts to analyse the global hydrological cycle are hampered by a deficiency of suitable observations, particularly over the oceans. Fully coupled general circulation models are potentially powerful tools in interpreting the limited observational data in the context of large-scale freshwater exchanges. We have looked at large-scale aspects of the global freshwater budget in a simulation, of over 1000 years, by the Hadley Centre coupled climate model (HadCM3). Many aspects of the global hydrological cycle are well represented, but the model hydrological cycle appears to be too strong, with overly large precipitation and evaporation components in comparison with the observational datasets we have used. We show that the ocean basin-scale meridional transports of freshwater come into near balance with the surface freshwater fluxes on a time scale of about 400 years, with the major change being a relative increase of freshwater transport from the Southern Ocean into the Atlantic Ocean. Comparison with observations, supported by sensitivity tests, suggests that the major cause of a drift to more saline condition in the model Atlantic is an overestimate of evaporation, although other freshwater budget components may also play a role. The increase in ocean freshwater transport into the Atlantic during the simulation, primarily coming from the overturning circulation component, which changes from divergent to convergent, acts to balance this freshwater budget deficit. The stability of the thermohaline circulation in HadCM3 may be affected by these freshwater transport changes and this question is examined in the context of an existing conceptual model.
TL;DR: In this paper, the impact of land use on hydrological processes in the Aguima catchment in West-Africa has been investigated using the GLOWA IMPETUS project.
Abstract: This paper analyzes the hydrological processes and the impact of soil properties and land use on these processes in tropical headwater catchment in the sub-humid part of Benin (West-Africa), the Aguima catchment. The presented study is integrated in the GLOWA IMPETUS project, which investigates the effects of global change on the water cycle and water availability on a regional scale in Morocco and Benin. The lack of field investigations concerning soil and surface hydrology in the Benin research area necessitates detailed field measurements including measurements of discharge, soil water dynamics, soil physical properties etc. on the local scale in order to understand the dominant runoff generation processes and its influencing factors. This is a pre-requisite to be able to forecast the effects which global change has on hydrological processes and water availability in the region. The paper gives an overview over the hydrologic measuring concept of the IMPETUS-Benin project focusing on measurements concerning the soil saturated conductivity ksat and discharge behaviour of two different sub-catchment of the Aguima catchment. The results of ksat measurements revealed that interflow is the dominant runoff process on the hillslopes of the investigated catchment. Concerning the impact of land use on the hydrological processes infiltration experiments showed that infiltration rates were reduced on cultivated land compared to natural land cover. This results in significant differences in runoff behaviour and runoff ratios while comparing natural and agricultural used catchments.
TL;DR: In this paper, the authors investigated water balance components in the three major river basins of Siberia (the Lena, Yenisey, and Ob) based on the National Centers for Environmental Prediction (NCEP)-Department of Energy (DOE) Atmospheric Model Intercomparison Project II (AMIP-II) reanalysis.
Abstract: This study investigated water balance components in the three major river basins of Siberia (the Lena, Yenisey, and Ob) based on the National Centers for Environmental Prediction (NCEP)–Department of Energy (DOE) Atmospheric Model Intercomparison Project II (AMIP-II) reanalysis. The primary focus is the nature of the interannual signatures of summer precipitation, moisture convergence, and runoff in individual basins, and their linkage to the large-scale water transport and circulation fields over northern Eurasia from 1979 to 1995. The temporal characteristics of the hydrological cycle and the associated large-scale circulation structure are discussed. Some interesting features are found in the interannual variability of basin-scale hydrometeorological elements. In the Lena and Ob basins, the temporal signatures of both precipitation and moisture convergence indicate a cycle of approximately 6 to 8 yr. The mid- and late-summer runoff variation is significantly correlated with these two elements....
TL;DR: The pan-Arctic water balance model (P/WBM) as mentioned in this paper was developed to simulate the high-latitude water cycle, along with comparisons with observed data across the pan Arctic drainage basin.
Abstract: A terrestrial hydrological model, developed to simulate the high-latitude water cycle, is described, along with comparisons with observed data across the pan-Arctic drainage basin. Gridded fields of plant rooting depth, soil characteristics (texture, organic content), vegetation, and daily time series of precipitation and air temperature provide the primary inputs used to derive simulated runoff at a grid resolution of 25 km across the pan-Arctic. The pan-Arctic water balance model (P/WBM) includes a simple scheme for simulating daily changes in soil frozen and liquid water amounts, with the thaw–freeze model (TFM) driven by air temperature, modelled soil moisture content, and physiographic data. Climate time series (precipitation and air temperature) are from the National Centers for Environmental Prediction (NCEP) reanalysis project for the period 1980–2001.
P/WBM-generated maximum summer active-layer thickness estimates differ from a set of observed data by an average of 12 cm at 27 sites in Alaska, with many of the differences within the variability (1σ) seen in field samples. Simulated long-term annual runoffs are in the range 100 to 400 mm year−1. The highest runoffs are found across northeastern Canada, southern Alaska, and Norway, and lower estimates are noted along the highest latitudes of the terrestrial Arctic in North America and Asia. Good agreement exists between simulated and observed long-term seasonal (winter, spring, summer–fall) runoff to the ten Arctic sea basins (r = 0·84). Model water budgets are most sensitive to changes in precipitation and air temperature, whereas less affect is noted when other model parameters are altered. Increasing daily precipitation by 25% amplifies annual runoff by 50 to 80% for the largest Arctic drainage basins. Ignoring soil ice by eliminating the TFM sub-model leads to runoffs that are 7 to 27% lower than the control run. The results of these model sensitivity experiments, along with other uncertainties in both observed validation data and model inputs, emphasize the need to develop improved spatial data sets of key geophysical quantities (particularly climate time series) to estimate terrestrial Arctic hydrological budgets better. Copyright © 2003 John Wiley & Sons, Ltd.
TL;DR: In this paper, the water vapor transport model at the regional boundary in the Meiyu period is put forward through diagnostic analysis, and the numerical simulation on the water vapour transport at the boundary of China in the heavy rainfall period during June-July 1998 shows that the feature of water vapor transfer in June is different from that in July.
Abstract: The water vapor transport model at the regional boundary in the Meiyu period is put forward through diagnostic analysis. The numerical simulation on the water vapor transport at the boundary of China in the heavy rainfall period during June–July 1998 shows that the feature of water vapor transport in June is different from that in July. The main body of the water cycle that forms the torrential rain in the Yangtze River Valley is made up of water vapor transport at the western and southern boundaries of the China region in June, whereas the water vapor flow at the western boundary in middle Tibet turns out to be the main body of water vapor sources in July. The water vapor transport at the western boundary of the Tibetan Plateau and the southern boundary of China plays an important role in the torrential rain in the Yangtze River Valley. The temporal and spatial distribution characteristics of water vapor flow at the regional boundary and their theoretical model would provide the scientific proof for the heavy rain forecasts in the Yangtze River Valley.