Global hydrology is concerned with the role of the terrestrial hydrological cycle in System Earth. In particular it focuses on the role of climate variability on global hydrology and the modelling of global water scarcity and groundwater depletion. To this purpose we have built a next-generation global hydrological model PCR-GLOBWB. The model has been used in various global or continental change analyses, such as the assessment of global nutrient dynamics, methane emissions, global water stress assessment, global flood risk analysis and global seasonal streamflow forecasting.
Our global hydrological research encompasses the following focus areas:
Global Water Scarcity and groundwater depletion
Global population and economic growth and the expansion of irrigated areas lead to an exponential increase in human water use since the 1960. Climate change on the other hand is expected to increase the probability and severity of droughts in already drought-prone areas of the world. The result is an increasing gap between water availability and human water demand, leading to water scarcity or water stress. We have developed the global hydrological model PCR-GLOBWB to model water availability. At the same time we have developed scripts to estimate human water demand from socio-economic data (land cover, GDP, population density, electricity use etc.). PCR-GLOBWB 1.0 and the water demand scripts PCR-GDEM operate at 0.5o globally, are coded in PCRaster and soon available for download. We have recently developed PCR-GLOBWB 2.0 that operates at 6 minutes globally and is coded in PCRaster-Python. It is still in development. In PCR-GLOBWB 2.0 we will include water demand calculation and fully integrate demand-driven water withdrawal, consumptive water use and return flows as part of the global hydrological cycle. An important addition to other global analyses in the literature is that we include non-renewable groundwater abstraction or groundwater depletion (se example). Operational services for water scarcity forecasting are being developed within the EU project GLOWASIS.
a) Simulated yearly average groundwater recharge by PCR-GLOBWB (1960-2000), b) total groundwater abstraction for the year 2000 and c) groundwater depletion (all figures in 10-3 km3 a-1). d) movie showing development of groundwater depletion 1960-2000 (Source: Wada, et al, 2010, Global depletion of groundwater resources. Geophysical Research Letters L20402).
The Groundwater footprint: The dark-blue areas have a groundwater footprint of less than 1; groundwater extraction is sustainable here in the long term as well. However, the red areas in Northern America and Asia have a much larger groundwater footprint. The footprint of the Upper Ganges is actually 54 times larger. The area would have to be 54 times larger to capture the precipitation needed to sustain current groundwater extraction. Groundwater in areas with a large groundwater footprint is severely depleted. The bar chart shows that the groundwater footprint is less than 1 for most areas (80%). The groundwater is being used sustainably here (Source: Gleeson et al., Water balance of global aquifers revealed by groundwater footprint. Nature 488 197–200).
- Wada, Y., L. P.H. van Beek, C. M. van Kempen, J. W.T.M. Reckman, S. Vasak, and M. F.P. Bierkens, 2010. Global depletion of groundwater resources. Geophysical Research Letters L20402.
- Van Beek, L.P.H., Y. Wada and Bierkens, M.F.P. 2011. Global monthly water stress: 1. Water balance and water availability, Water Resources Research 47, W07517.
- Wada, Y., L.P.H. van Beek, D. Viviroli, H.H. Dürr, R. Weingartner, and M.F.P. Bierkens, 2011. Global monthly water stress: 2. Water demand and severity of water stress, Water Resources Research 47, W07518.
- Wada, Y., L.P.H. van Beek, F.C. Sperna Weiland, B.F. Chao, Y.-H. Wu, and M.F.P. Bierkens ,2012., Past and future contribution of global groundwater depletion to sea-level rise, Geophysical Research Letters 39, L09402.
- Gleeson, T,Y. Wada, M.F.P. Bierkens, L.P.H. van Beek, 2012. Water balance of global aquifers revealed by groundwater footprint. Nature 488 197–200.
Global floods and droughts (climate impacts, climate feedbacks and forecasting
Apart from considering the detrimental effects from human water consumption, the occurrence of floods and droughts due to climate variability and climate change is an important area of research. In this focus area we study a) the effects of climate change on river flow (floods and droughts), b) the relation between land surface conditions evaporation and precipitation recycling, c) seasonal forecasting of river flow and soil moisture. Apart from the global hydrological model PCR-GLOBWB, we also employ statistical analyses and conceptual modelling approaches. Research under this theme is done in close cooperation with Deltares.
A new way of dealing with multi-GCM uncertainty: maps showing the number of models projecting significant change (compared to GCM-specific year-to-year variation; significance level of 95%) in the same direction as the ensemble mean direction of of change. From top to bottom the figure shows GCM-consistencies for yearly maximum, mean and minimum discharge. Negative values correspond to the number of models showing discharge decrease, positive values correspond to the number of models projecting discharge increase, grey areas correspond to areas with no significant change (Source: Sperna Weiland, F.C., L.P.H. van Beek, J. C.J. Kwadijk, and M.F.P. Bierkens, 2011. Global patterns of change in discharge regimes for 2100. Hydrology and Earth System Science, 16, 1047-1062, 2012)
- Lam, A.H., M.F.P. Bierkens and B.J.J.M. van den Hurk, 2007. Global patterns of relations between soil moisture and rainfall occurrence in ERA-40. Journal of Geophysical Research 112, D18101.
- Bierkens, M.F.P. and B.J.J.M. van den Hurk, 2007. Groundwater convergence as a possible mechanism for multi-year persistence in rainfall. Geophysical Research Letters 34, L02402.
- Bierkens, M.F.P. and L.P. van Beek, 2009. Seasonal Predictability of European Discharge: NAO and hydrological response time. Journal of Hydrometeorology 10, 953–968.
- Sperna Weiland, F.C., L.P.H. van Beek, J. C.J. Kwadijk, and M.F.P. Bierkens, 2011. Global patterns of change in discharge regimes for 2100. Hydrology and Earth System Science16, 1047-1062, 2012.
- Sperna Weiland, FC, L.P.H. van Beek, A.H. Weerts, M.F.P. Bierkens, 2011. Extracting information from an ensemble of GCMs to reliably assess future global runoff change. Journal of Hydrology 412, 66-75.
Water Towers of the Himalaya
The mountains of the Hindu Kush, Karakoram and the Himalaya in East Asia (HKH region for short) harbour the largest glaciers and snow stores in the world. Their fate under climate change has been heavily debated, with many contrasting reports of both disappearing and growing glaciers. We as hydrologists have asked ourselves a much more important question: how important are glaciers and snow of the HKH region for downstream water availability (and ultimately food security)? To answer these questions we are combining models of glacier dynamics and hydrological models with field data and remote sensing information. Central to this research line is the projects of Walter Immerzeel who keeps his own website on the subject.
This sequence of pictures shows the 21st century ensemble mean projection of the ice thickness of the Baltoro glacier in the Karakoram mountain range for 2010-2070. Projections were made with a dynamic glacier model (see Immerzeel et al., Climatic Change in press) forced with an ensemble of five statistically downscaled GCM runs (see nature Geoscience doi:10.1038/ngeo1896, 2013)
- Immerzeel, W.W., P. Droogers, S.M. de Jong and M.F.P. Bierkens, 2009. Large-scale monitoring of snow cover and runoff simulation in Himalayan river basins using remote sensing. Remote Sensing of Environment 113, 40-49.
- Immerzeel, W.W. and M.F.P. Bierkens, 2009. Seasonal prediction of monsoon rainfall in three Asian river basins: the importance of snow cover on the Tibetan Plateau. International Journal of Climatology (2009) .doi:10.1002/joc
- Immerzeel, W.W., L.P.H. Van Beek and M.F.P. Bierkens, 2011. Climate change will affect the Asian water towers. Science 328, 1382-5.
- Immerzeel, W.W., L.P.H. van Beek, M. Konz, A.B. Shrestha and M.F.P. Bierkens, 2011. Hydrological response to climate change in a glacierized catchment in the Himalayas. Climatic Change 110, 721-736.
- Immerzeel, W.W., F. Pellicciotti and M.F.P. Bierkens, 2013. Rising river flows throughout the twenty-first century in two Himalayan glacierized watersheds. Nature Geoscience, doi:10.1038/ngeo1896.
Other global and regional studies
Apart from the three themes shown above, we also apply PCR-GLOBWB or regional versions thereof to a variety of environmental issues. Examples are the simulation of soil wetness, groundwater depth and inundation depth to calculate methane emissions, the simulation of global surface water temperature, mapping global wetland extent, simulation of continental-scale nutrient export and high-resolution coupled groundwater-surface water modelling. Future work will focus on the high-resolution modelling of lateral terrestrial N,P,C transport and the associated biogeochemistry in cooperation with the groups of Prof. Hans Middelkoop and Prof. Jack Middelburg.
This image shows circumpolar yearly average CH4 fluxes estimated with the PEATLAND VU model (VU University Amsterdam), with wetland extent and soil parameterization according to the FAO(ISRIC) digital soil map of the world and with soil wetness, water table depth and inundation depth from PCR-GLOBWB (Source: Petrescu, A. M. R., L. P. H. van Beek et al., 2010. Modeling regional to global CH4 emissions of boreal and arctic wetlands, Global Biogeochemical Cycles 24, GB4009)
- Loos, S., H. Middelkoop, L.P.H. van Beek and M. van der Perk, 2009. Large scale nutrient modelling using globally available datasets: a test for the Rhine basin. Journal of Hydrology 369, 403-415.
- Petrescu, A. M. R., L. P. H. van Beek, J. van Huissteden, C. Prigent, T. Sachs, C. A. R. Corradi, F. J. W. Parmentier, and A. J. Dolman, 2010. Modeling regional to global CH4 emissions of boreal and arctic wetlands. Global Biogeochemical Cycles 24, GB4009.
- E. H. Sutanudjaja, L. P. H. van Beek, S. M. de Jong, F. C. van Geer, and M. F. P. Bierkens, 2011. Large-scale groundwater modeling using global datasets: a test case for the Rhine-Meuse basin. Hydrology and Earth System Science 15, 2913-2935.