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Wai Kwok Wong, Stein Beldring, Torill Engen-Skaugen, Ingjerd Haddeland, and Hege Hisdal

situations occurred in 2006, 2002/03, and 1995/96. Trend studies indicate that summer droughts in southern Norway have become more severe ( Wilson et al. 2010 ), and according to the latest Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report ( Solomon et al. 2007 ), most atmosphere–ocean general circulation models (AOGCMs) project an increased dryness of summer soil moisture across large areas of the northern middle and high latitudes. Summer and winter droughts can be distinguished

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Lukas Gudmundsson, Lena M. Tallaksen, Kerstin Stahl, Douglas B. Clark, Egon Dumont, Stefan Hagemann, Nathalie Bertrand, Dieter Gerten, Jens Heinke, Naota Hanasaki, Frank Voss, and Sujan Koirala

discharge from large, continental-scale river basins. Generally these studies show that the uncertainty in river discharge introduced by the use of different atmospheric forcing models ( Nohara et al. 2006 ; Hagemann and Jacob 2007 ) and different land surface schemes ( Materia et al. 2010 ) can be reduced by ensemble techniques. Several studies have compared soil moisture simulations from the GSWP to monthly observations from a global observation network (e.g., Gao and Dirmeyer 2006 ; Guo and

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G. P. Weedon, S. Gomes, P. Viterbo, W. J. Shuttleworth, E. Blyth, H. Österle, J. C. Adam, N. Bellouin, O. Boucher, and M. Best

calculate changes in hydrologically important variables such as evaporation, soil moisture, and runoff ( Haddeland et al. 2011 ). For both types of model, meteorological “forcing” (or “driving”) data (air temperature, rainfall/snowfall, etc.) are required at subdaily time steps for the LSMs and daily time steps for the GHMs. The 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) product, which provided the basis data used in the derivation of the WFD, was derived from

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Pete Falloon, Richard Betts, Andrew Wiltshire, Rutger Dankers, Camilla Mathison, Doug McNeall, Paul Bates, and Mark Trigg

four soil layers, each with a temperature and moisture content, and the four soil layers have thicknesses from the surface downward of 0.1, 0.25, 0.65, and 2.0 m. On the surface, there are lying snow and canopy water stores. The canopy water is the rainfall intercepted by plant leaves that is available for free evaporation. The method of partitioning precipitation into canopy interception and throughfall is described by Dolman and Gregory (1992) . The total moisture flux from the surface is made

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Richard Harding, Martin Best, Eleanor Blyth, Stefan Hagemann, Pavel Kabat, Lena M. Tallaksen, Tanya Warnaars, David Wiberg, Graham P. Weedon, Henny van Lanen, Fulco Ludwig, and Ingjerd Haddeland

.g., Cess et al. 1991 ). However, feedbacks between CO 2 , vegetation, soil moisture, groundwater recharge, and climate are less well understood and are not well described in most climate and hydrological models. Over 18% of total cultivated land is irrigated ( Fischer et al. 2007 ); additionally, much nonagricultural land has been substantially modified by human activities. Conversion of land to agriculture not only impacts the local evaporation and hydrological response, but may also influence the

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Stefan Hagemann, Cui Chen, Jan O. Haerter, Jens Heinke, Dieter Gerten, and Claudio Piani

seasonal phenology of natural and agricultural vegetation are simulated based on long-term average climate. The model distinguishes two soil layers with fixed thickness (upper, 50 cm; lower, 100 cm). Soil moisture of each layer is updated daily, according to the balance between the amount of water infiltrating into the soil (throughfall minus surface runoff) and that removed from the soil layers through subsurface runoff, percolation, soil evaporation, and plant transpiration. Evapotranspiration is

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Kerstin Stahl, Lena M. Tallaksen, Lukas Gudmundsson, and Jens H. Christensen

1. Introduction Large-scale gridded models, including global (general circulation) and regional climate models and large-scale hydrological models, are employed for a variety of purposes in hydrology and related disciplines. They provide spatial simulations of hydrological variables such as soil moisture, runoff, and river discharge for historical records and can be used to simulate the response of the hydrological cycle to future global change, that is, climate scenarios and human impacts

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Aristeidis G. Koutroulis, Aggeliki-Eleni K. Vrohidou, and Ioannis K. Tsanis

and the duration of the dry period, while agricultural drought refers to situations in which the soil moisture is no longer sufficient to meet the needs of the crops growing in the area, focusing on properties such as precipitation shortage, differences between potential and actual evapotranspiration, and soil moisture deficits. Finally, hydrological drought associates the effect of periods of precipitation shortfalls on surface or subsurface water supply ( Wilhite 2000 ). In spite of the fact

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Philippe Lucas-Picher, Jens H. Christensen, Fahad Saeed, Pankaj Kumar, Shakeel Asharaf, Bodo Ahrens, Andrew J. Wiltshire, Daniela Jacob, and Stefan Hagemann

. They suggested that the overestimation of precipitation over the mountain ranges (Western Ghats) and warm oceans seems to remove moisture from the atmosphere and to generate weak precipitation over land (as observed in central India). The HIRHAM5 model has a dry bias in Bangladesh and Myanmar and exaggerates precipitations on the east coast of India. As observed for other simulations over Africa and Europe, the HIRHAM5 model seems to generate too much precipitation on the coast and has difficulty

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Christel Prudhomme, Simon Parry, Jamie Hannaford, Douglas B. Clark, Stefan Hagemann, and Frank Voss

cycle that are directly influenced by anthropogenic forcing (e.g., increased evaporation through higher temperatures and increased rainfall as a result of higher moisture holding capacity in a warmer atmosphere), one of the most important potential impacts of climate change is on hydrological extremes (i.e., drought and flooding). Extremes are likely to be sensitive to climate change, raising the possibility that changes in the extremes of hydrological parameters may be more detectable than changes

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