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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

pressure, (iv) specific humidity at 2 m, (v) downward longwave radiation flux, (vi) downward shortwave radiation flux, (vii) rainfall rate, and (viii) snowfall rate. These global data are stored at 67 420 points over land (excluding the Antarctic), with the land–sea mask used being that defined by the Climatic Research Unit (CRU; New et al. 1999 , 2000 ) in netCDF format using the Assistance for Land-Surface Modelling Activities (ALMA) convention (see http

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

processes, gravity wave drag, microphysics, and sea ice schemes, plus major changes to convection, land surface, and cloud schemes, and inclusion of aerosols; a detailed comparison of the two models is given by Martin et al. (2006) and Johns et al. (2006) . Compared to HadCM3, the developments to HadGEM1 have led to a substantial improvement in the processes represented, including the hydrological cycle, particularly for oceanic surface freshwater fluxes ( Rodriguez et al. 2010 ). The hydrological

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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

, both these influences may lead to enhanced vegetation growth (and hence leaf area), enhancing further evaporation ( Gerten and Gedney 2008 ). Long-term trends have been noted from the pan evaporation datasets ( Roderick et al. 2007 ; Roderick and Farquhar 2002 ), which have been ascribed to changes in aerosols causing changes in incoming solar radiation ( Wild et al. 2005 ). Jung et al. (2010) show, from an analysis of the direct measurements from the Flux Network (FLUXNET) and models, that

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Ingjerd Haddeland, Douglas B. Clark, Wietse Franssen, Fulco Ludwig, Frank Voß, Nigel W. Arnell, Nathalie Bertrand, Martin Best, Sonja Folwell, Dieter Gerten, Sandra Gomes, Simon N. Gosling, Stefan Hagemann, Naota Hanasaki, Richard Harding, Jens Heinke, Pavel Kabat, Sujan Koirala, Taikan Oki, Jan Polcher, Tobias Stacke, Pedro Viterbo, Graham P. Weedon, and Pat Yeh

1. Introduction The global water balance has been the subject of modeling studies for decades, both from a climate perspective where the main interest is the influence of the water balance on surface heat fluxes and from a hydrological perspective focusing on water availability and use. However, there are still many uncertainties in our understanding of the current water cycle, and to date the results of land surface models (LSMs) and global hydrology models (GHMs) have not been compared in a

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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

1. Introduction Large-scale hydrological models have proved to be valuable tools for assessing fluctuations in terrestrial water stores and fluxes on continental and global scales (e.g., Dirmeyer 2011 ; Dirmeyer et al. 2006 ; Milly et al. 2005 ). To date, models describing the terrestrial water balance have been developed by different communities and parallel terminologies, and modeling philosophies have emerged ( Haddeland et al. 2011 ). Among the most commonly used terms are global

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

data on these processes from all regions in Norway. Runoff and evapotranspiration fluxes determined by the HBV model are usually realistic when observed precipitation, temperature, and streamflow data are available for model calibration. b. Definition of summer season and threshold level Model simulations produced gridded daily time series of soil moisture, runoff, and groundwater. These datasets, together with the downscaled precipitation data, constituted the basis of this study. Although the HBV

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

on the accuracy of the GCM data, especially of precipitation. An accurate representation of the exchange of water among the atmosphere, the ocean, the cryosphere, and the land surface is one of the biggest challenges in global climate modeling. Simulating these fluxes is extremely difficult because they depend on processes occurring on spatial scales that are generally several orders of magnitude smaller than the typical grid size in a GCM. The formation of precipitation, for example, is

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

( Best et al. 2011 ; Clark et al. 2011 ) is the land surface scheme used in the climate models of the Met Office. It includes mechanistic descriptions of the processes that control the exchanges of energy, momentum, water, and carbon between the land surface and the atmosphere. The energy balance of the surface is calculated on a time step of one hour or less and there is a multilayer snow model. Fluxes of water and heat in the soil are represented using four soil layers with a total depth of 3 m

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

surface scheme that aimed to compare simulations with river flow in large basins commonly subject the two fluxes (runoff and drainage) that leave a grid cell to a channel routing scheme (e.g., Hagemann and Dümenil Gates 2003 ). 3. Methods a. Corresponding observed and simulated runoff time series For each observed streamflow series Q obs ( t ), a corresponding daily time series of simulated basin runoff Q sim ( t ) was obtained as where i are the individual grid cells of the total number of n

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D. Gerten, J. Heinke, H. Hoff, H. Biemans, M. Fader, and K. Waha

(around year 2000) cropland distribution ( Ramankutty et al. 2008 ) with a dataset of maximum monthly irrigated and rain-fed harvested areas of 26 crops ( Portmann et al. 2010 ) that we aggregated to the CFTs (see Fader et al. 2010 ). The fractions of CFTs and grazing land were held constant at the year 2000 level throughout the simulation period (also in the past) in order to minimize effects of factors other than climate and population. Carbon fluxes and pools as well as water fluxes (evaporation

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