The future for global water assessment
Harding, R.J. ; Weedon, G.P. ; Lanen, H.A.J. van; Clark, D.B. - \ 2014
Journal of Hydrology 518 (2014). - ISSN 0022-1694 - p. 186 - 193.
multimodel ensemble - bias correction - climate - precipitation - model - runoff - impact - 20th-century - temperature - drought
The global water cycle is a fundamental component of our climate and Earth system. Many, if not the majority, of the impacts of climate change are water related. We have an imperfect description and understanding of components of the water cycle. This arises from an incomplete observation of some of the stores and fluxes in the water cycle (in particular: precipitation, evaporation, soil moisture and groundwater), problems with the simulation of precipitation by global climate models and the wide diversity of global hydrological models currently in use. This paper discusses these sources of errors and, in particular, explores the errors and advantages of bias correcting climate model outputs for hydrological models using a single large catchment as an example (the Rhine). One conclusion from this analysis is that bias correction is necessary and has an impact on the mean flows and their seasonal cycle. However choice of hydrological model has an equal, if not larger effect on the quality of the simulation. The paper highlights the importance of improving hydrological models, which run at a continental and global scale, and the importance of quantifying uncertainties in impact studies.
Multimodel estimate of the global terrestrial water balance: Setup and first results
Haddeland, I. ; Clark, D. ; Franssen, W.H.P. ; Ludwig, F. ; Voss, F. ; Arnell, N.W. ; Bertrand, N. ; Best, M. ; Folwell, S. ; Gerten, D. ; Gomes, S. ; Gosling, S. ; Hagemann, S. ; Hanasaki, N. ; Harding, R. ; Heinke, J. ; Kabat, P. ; Koirala, S. ; Oki, T. ; Polcher, J. ; Stacke, T. ; Viterbo, P. ; Weedon, G.P. ; Yeh, P. - \ 2011
Journal of Hydrometeorology 12 (2011)5. - ISSN 1525-755X - p. 869 - 884.
land-surface scheme - space-time climate - parameterization schemes - integrated model - project - simulation - resources - runoff - gcm - precipitation
Six land surface models and five global hydrological models participate in a model intercomparison project [Water Model Intercomparison Project (WaterMIP)], which for the first time compares simulation results of these different classes of models in a consistent way. In this paper, the simulation setup is described and aspects of the multimodel global terrestrial water balance are presented. All models were run at 0.5° spatial resolution for the global land areas for a 15-yr period (1985–99) using a newly developed global meteorological dataset. Simulated global terrestrial evapotranspiration, excluding Greenland and Antarctica, ranges from 415 to 586 mm yr-1 (from 60 000 to 85 000 km3 yr-1), and simulated runoff ranges from 290 to 457 mm yr-1 (from 42 000 to 66 000 km3 yr-1). Both the mean and median runoff fractions for the land surface models are lower than those of the global hydrological models, although the range is wider. Significant simulation differences between land surface and global hydrological models are found to be caused by the snow scheme employed. The physically based energy balance approach used by land surface models generally results in lower snow water equivalent values than the conceptual degree-day approach used by global hydrological models. Some differences in simulated runoff and evapotranspiration are explained by model parameterizations, although the processes included and parameterizations used are not distinct to either land surface models or global hydrological models. The results show that differences between models are a major source of uncertainty. Climate change impact studies thus need to use not only multiple climate models but also some other measure of uncertainty (e.g., multiple impact models).
Reference evapotranspiration with radiation-based and temperature-based method - impact on hydrological drought using WATCH Forcing Data
Melsen, L.A. ; Wanders, N. ; Huijgevoort, M.H.J. van; Weedon, G.P. - \ 2011
Brussel : European Commission (Technical report / WATCH no. 39) - 67
evapotranspiratie - hydrologie - hydrologische gegevens - droogte - evapotranspiration - hydrology - hydrological data - drought
Simulation of low flows and drought events in WATCH test basins: impact of climate forcing datasets
Huijgevoort, M.H.J. van; Loon, A.F. van; Hanel, M. ; Haddeland, I. ; Horvát, O. ; Koutroulis, A. ; Machlica, A. ; Weedon, G.P. ; Fendeková, M. ; Tsanis, I. ; Lanen, H.A.J. van - \ 2011
2011 : European Commission (Technical report / WATCH no. 44) - 19
geohydrologie - gegevensanalyse - resolutie - aardoppervlak - afvloeiingswater - bodemwater - klimatologie - evaporatie - geohydrology - data analysis - resolution - land surface - runoff water - soil water - climatology - evaporation
The impact of both spatial and temporal resolution on the components of the terrestrial hydrological cycle are investigated using the WATCH forcing dataset (WFD) and the JULES (Joint UK Land Environment Simulator) land surface model. The various spatial resolutions are achieved by degrading the native half degree latitude/longitude resolution WATCH dataset to both one degree and two degrees. The temporal resolutions are created by degrading the native three hourly WATCH forcing dataset to six hourly and using the WATCH interpolator to derive a one hour forcing dataset. There is little difference in the moisture stores of soil water and canopy water in the long term mean from the various resolutions, so the analysis presented is for the changes in evaporation and runoff. The evaporation is further analysed into its various components for the spatial resolution. Results suggest that there is little impact from spatial resolution, but the interpolation method for temporal resolution can have a significant effect on the total mean evaporation/runoff balance.
Executive summary of the completed WATCH project
Harding, R. ; Warnaars, T. ; Weedon, G.P. ; Wiberg, D. ; Hagemann, S. ; Tallaksen, L. ; Lanen, H.A.J. van; Blyth, E. ; Ludwig, F. ; Kabat, P. - \ 2011
Brussel : European Commission (Technical report / WATCH no. 56) - 65
Multi-model analysis of drought at the global scale: differences in Hydrological drought between the first and the second part of the 20th Centrury
Estifanos, S. ; Huijgevoort, M.H.J. van; Hazenberg, P. ; Lanen, H.A.J. van; Weedon, G.P. - \ 2011
Brussel : European Commission (Technical report / WATCH no. 40) - 48
Watch: Current knowledge of the terrestrial Global Water Cycle"
Harding, R. ; Best, M. ; Hagemann, S. ; Kabat, P. ; Tallaksen, L.M. ; Warnaars, T. ; Wiberg, D. ; Weedon, G.P. ; Lanen, H.A.J. van; Ludwig, F. ; Haddeland, I. - \ 2011
Journal of Hydrometeorology 12 (2011)6. - ISSN 1525-755X - p. 1149 - 1156.
climate-change projections - rainfall-runoff model - river - precipitation - trends - requirements - availability - streamflow - dataset - surface
Water-related impacts are among the most important consequences of increasing greenhouse gas concentrations. Changes in the global water cycle will also impact the carbon and nutrient cycles and vegetation patterns. There is already some evidence of increasing severity of floods and droughts and increasing water scarcity linked to increasing greenhouse gases. So far, however, the most important impacts on water resources are the direct interventions by humans, such as dams, water extractions, and river channel modifications. The Water and Global Change (WATCH) project is a major international initiative to bring together climate and water scientists to better understand the current and future water cycle. This paper summarizes the underlying motivation for the WATCH project and the major results from a series of papers published or soon to be published in the Journal of Hydrometeorology WATCH special collection. At its core is the Water Model Intercomparison Project (WaterMIP), which brings together a wide range of global hydrological and land surface models run with consistent driving data. It is clear that we still have considerable uncertainties in the future climate drivers and in how the river systems will respond to these changes. There is a grand challenge to the hydrological and climate communities to both reduce these uncertainties and communicate them to a wider society
Global river temperatures and sensitivity to atmospheric warming and changes in river flow
Vliet, M.T.H. van; Ludwig, F. ; Zwolsman, J.J.G. ; Weedon, G.P. ; Kabat, P. - \ 2011
Water Resources Research 47 (2011)2. - ISSN 0043-1397 - 19 p.
water temperature - air-temperature - stream temperatures - climate-change - thermal regime - united-states - new-brunswick - variability - models - canada
This study investigates the impact of both air temperature and river discharge changes on daily water temperatures for river stations globally. A nonlinear water temperature regression model was adapted to include discharge as a variable in addition to air temperature, and a time lag was incorporated to apply the model on a daily basis. The performance of the model was tested for a selection of study basin stations and 157 river temperature stations globally using historical series of daily river temperature, air temperature, and river discharge for the 1980–1999 period. For the study basin stations and for 87% of the global river stations, the performance of the model improved by including discharge as an input variable. Greatest improvements were found during heat wave and drought (low flow) conditions, when water temperatures are most sensitive to atmospheric influences and can reach critically high values. A sensitivity analysis showed increases in annual mean river temperatures of +1.3 °C, +2.6 °C, and +3.8 °C under air temperature increases of +2 °C, +4 °C, and +6 °C, respectively. Discharge decreases of 20% and 40% exacerbated water temperature increases by +0.3 °C and +0.8 °C on average. For several stations, maximum water temperatures on a daily basis were higher under an air temperature increase of +4 °C combined with a 40% discharge decrease compared to an air temperature increase of +6 °C (without discharge changes). Impacts of river discharge on water temperatures should therefore be incorporated to provide more accurate estimations of river temperatures during historical and future projected dry and warm periods
Evaluating the JULES Land Surface Model Energy Fluxes Using FLUXNET Data
Blyth, E. ; Gash, J.H.C. ; Lloyd, A.J. ; Pryor, M. ; Weedon, G.P. ; Shuttleworth, J. - \ 2010
Journal of Hydrometeorology 11 (2010)2. - ISSN 1525-755X - p. 509 - 519.
anemometer (co)sine response - experiment ebex-2000 - tropical forest - field data - part ii - evaporation - balance - storage - canopy - water
Surface energy flux measurements from a sample of 10 flux network (FLUXNET) sites selected to represent a range of climate conditions and biome types were used to assess the performance of the Hadley Centre land surface model (Joint U. K. Land Environment Simulator; JULES). Because FLUXNET data are prone systematically to undermeasure surface fluxes, the model was evaluated by its ability to partition incoming radiant energy into evaporation and how such partition varies with atmospheric evaporative demand at annual, seasonal, weekly, and diurnal time scales. The model parameters from the GCM configuration were used. The overall performance was good, although weaknesses in model performance were identified that are associated with the specification of the leaf area index and plant rooting depth, and the representation of soil freezing.