Hydrology and Earth System Sciences www.hydrol-earth-syst-sci.net 1027-5606 1607-7938 12 4 2008 10.5194/hess-12-1027-2008 http://www.hydrol-earth-syst-sci.net/12/1027/2008/ http://www.hydrol-earth-syst-sci.net/12/1027/2008/hess-12-1027-2008.html http://www.hydrol-earth-syst-sci.net/12/1027/2008/hess-12-1027-2008.pdf 1027 1037 2008-07-29 An integrated model for the assessment of global water resources – Part 2: Applications and assessments N. Hanasaki hanasaki@nies.go.jp S. Kanae T. Oki K. Masuda K. Motoya N. Shirakawa Y. Shen K. Tanaka National Institute for Environmental Studies, Japan Institute of Industrial Science, University of Tokyo, Japan Frontier Research Center for Global Change, Japan Faculty of Education and Human Studies, Akita University, Japan Graduate School of Systems and Information Engineering, University of Tsukuba, Japan Center for Agricultural Resources Research, The Chinese Academy of Sciences, China Disaster Prevention Research Institute, Kyoto University, Japan To assess global water resources from the perspective of subannual variation in water availability and water use, an integrated water resources model was developed. In a companion report, we presented the global meteorological forcing input used to drive the model and six modules, namely, the land surface hydrology module, the river routing module, the crop growth module, the reservoir operation module, the environmental flow requirement module, and the anthropogenic withdrawal module. Here, we present the results of the model application and global water resources assessments. First, the timing and volume of simulated agriculture water use were examined because agricultural use composes approximately 85% of total consumptive water withdrawal in the world. The estimated crop calendar showed good agreement with earlier reports for wheat, maize, and rice in major countries of production. In major countries, the error in the planting date was ±1 mo, but there were some exceptional cases. The estimated irrigation water withdrawal also showed fair agreement with country statistics, but tended to be underestimated in countries in the Asian monsoon region. The results indicate the validity of the model and the input meteorological forcing because site-specific parameter tuning was not used in the series of simulations. Finally, global water resources were assessed on a subannual basis using a newly devised index. This index located water-stressed regions that were undetected in earlier studies. These regions, which are indicated by a gap in the subannual distribution of water availability and water use, include the Sahel, the Asian monsoon region, and southern Africa. The simulation results show that the reservoir operations of major reservoirs (>1 km³) and the allocation of environmental flow requirements can alter the population under high water stress by approximately −11% to +5% globally. The integrated model is applicable to assessments of various global environmental projections such as climate change. Alcamo, J., Döll, P., Henrichs, T., Kaspar, F., Lehner, B., Rosch, T., and Siebert, S.: Development and testing of the WaterGAP 2 global model of water use and availability, Hydrolog. Sci. J., 48, 317–337, 2003a. Alcamo, J., Döll, P., Henrichs, T., Kaspar, F., Lehner, B., Rosch, T., and Siebert, S.: Global estimates of water withdrawals and availability under current and future "business-as-usual" conditions, Hydrolog. Sci. J., 48, 339–348, 2003b. Alcamo, J., Florke, M., and Marker, M.: Future long-term changes in global water resources driven by socio-economic and climatic changes, Hydrolog. Sci. J., 52, 247–275, 2007. Arnell, N. W.: Climate change and global water resources, Global. Environ. Chang., 9, S31–S49, 1999. Arnell, N. W.: Climate change and global water resources: SRES emissions and socio-economic scenarios, Global. Environ. Chang., 14, 31–52, 2004. Center for International Earth Science Information Network (CIESIN) Columbia University, and Centro Internacional de Agricultura Tropical (CIAT): Gridded Population of the World Version 3 (GPWv3): Population Grids, Socioeconomic Data and Applications Center (SEDAC) Columbia University, Palisades, NY, 2005. Döll, P. and Siebert, S.: A digital global map of irrigated areas, ICID J., 49, 55–66, 2000. Döll, P. and Siebert, S.: Global modeling of irrigation water requirements, Water Resour. Res., 38, 1037, doi:10.1029/2001WR000355, 2002. Döll, P., Kaspar, F., and Lehner, B.: A global hydrological model for deriving water availability indicators: model tuning and validation, J. Hydrol., 270, 105–134, 2003. Food and Agriculture Organization: FAOSTAT, http://faostat.fao.org/, last access: 29 July 2008. Food and Agriculture Organization: AQUASTAT, http://www.fao.org/ag/agl/aglw/aquastat/main/index.stm, last access: 29 July 2008. Hall, F. G., de Colstoun, E. B., Collatz, G. J., Landis, D., Dirmeyer, P., Betts, A., Huffman, G. J., Bounoua, L., and Meeson, B.: ISLSCP Initiative II global data sets: Surface boundary conditions and atmospheric forcings for land-atmosphere studies, J. Geophys. Res.-Atmos., 111, D22S01, doi:10.1029/2006JD007366, 2006. Hanasaki, N., Kanae, S., and Oki, T.: A reservoir operation scheme for global river routing models, J. Hydrol., 327, 22–41, 2006. Hanasaki, N., Kanae, S., Oki, T., Masuda, K., Motoya, K., Shirakawa, N., Shen, Y., and Tanaka, K.: An integrated model for the assessment of global water resources - Part 1: Model description and input meteorological forcing, Hydrol. Earth Syst. Sci., 12, 1007–1025, 2008. Hoekstra, A. Y. and Hung, P. Q.: Virtual water trade, A quantification of virtual water flows between nations in relation to international crop trade, Institute of Hydraulic Engineering (IHE), Delft, The Netherlands, 2002. Ishii, R., Nakaseko, K., and Takahashi, Y.: Agronomics, Asakura Publishing, Tokyo, Japan, 1999. Kundzewicz, Z. W., Mata, L. J., Arnell, N. W., Döll, P., Kabat, P., Jiménez, B., Miller, K. A., Oki, T., Sen, Z., and Shiklomanov, I. A.: Freshwater resources and their management, in: Climate Change 2007: impacts, adaptation and vulnerability, contribution of working group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, edited by: Parry, M. L., Canziani, O. F., Palutikof, J. P., van der Linden, P. J., and Hanson, C. E., Cambridge University Press, Cambridge, UK, 173–210, 2007. Leff, B., Ramankutty, N., and Foley, J. A.: Geographic distribution of major crops across the world, Global Biogeochem. Cy., 18, GB1009, doi:10.1029/2003GB002108, 2004. Oki, T. and Sud, Y. C.: Design of total runoff integrating pathways TRIP – a global river channel network, Earth Interactions, 2, 1–37, 1998. Oki, T., Agata, Y., Kanae, S., Saruhashi, T., Yang, D. W., and Musiake, K.: Global assessment of current water resources using total runoff integrating pathways, Hydrolog. Sci. J., 46, 983–995, 2001. Oki, T. and Kanae, S.: Virtual water trade and world water resources, Water Sci. Technol., 49, 203–209, 2004. Oki, T. and Kanae, S.: Global hydrological cycles and world water resources, Science, 313, 1068–1072, 2006. Ramankutty, N. and Foley, J. A.: Characterizing patterns of global land use: An analysis of global croplands data, Global Biogeochem. Cy., 12, 667–685, 1998. Raskin, P., Gleick, P., Kirshen, P., Pontius, G., and Strzepek, K.: Comprehensive assessment of the freshwater resources of the world, Stockholm Environment Institute, Stockholm, Sweden, 1997. Shiklomanov, I. A.: Appraisal and assessment of world water resources, Water Int., 25, 11–32, 2000. Shirakawa, N.: A conceptual framework for global estimation of environmental flow, J. Hydraul. Eng.-JSCE, 48, 421–426, 2004. Shirakawa, N.: Global estimation of environmental flow requirement based on river runoff seasonality, J. Hydraul. Eng.-JSCE, 49, 391–396, 2005. Smakhtin, V., Revenga, C., and Doll, P.: A pilot global assessment of environmental water requirements and scarcity, Water Int., 29, 307–317, 2004. Vörösmarty, C. J., Green, P., Salisbury, J., and Lammers, R. B.: Global water resources: vulnerability from climate change acid population growth, Science, 289, 284–288, 2000. World Agricultural Outlook Board US Department of Agriculture: Major world crop areas and climatic profile, US Department of Agriculture, Washington DC, USA, 1994.