Seasonal and Inter-Annual Variability of the Global Land Surface Water Budget.

Gopi Goteti1, J. Sheffield1, V. R. Sridhar1, J. Adam2, E. F. Wood1, and D. P. Lettenmaier2. (1) Princeton University, Princeton, NJ 08544, (2) University of Washington

Adequate water resources planning is hampered by a lack of information on the variability of the hydrological cycle. Determining how the components of the land surface water balance vary over seasonal and annual scales is critical in understanding how water resource management can address periods of drought or excess. The potential effects of climate change, and the impacts on climate variability can hopefully be addressed through global-scale modeling studies, given the lack of direct, long-term global-scale observations. A global, multi-decade, sub-daily, 1.0-degree dataset of the water and energy balance has been constructed using simulations of the Variable Infiltration Capacity (VIC) land surface model. This dataset provides long-term, globally consistent and validated land surface water and energy fluxes and states at a high temporal and spatial resolution. The simulation was forced with a meteorological dataset constructed from a combination of existing global datasets with corrections made for wind-induced gauge undercatch of precipitation and underestimation of precipitation in mountainous regions. Using this dataset, we analyze the seasonal and inter-annual variability in the major components of the land surface water balance including precipitation, evaporation, runoff, and changes in soil and snow storage. Where observations are available, we evaluate the magnitude of the simulated variability in these components, including comparison against observed variability in the runoff ratio for a number of major river basins. We also compare with control simulations from two climate models: the NCAR/DOE Parallel Climate Model (PCM) and the Max-Planck-Institute for Meteorology ECHAM model. Spatial variability in the response of the land surface is forced by the spatial variability in climate and the distribution of soil and vegetation type. The analysis shows that there exist large spatial differences in the storage and flux of water across the globe. Results will be presented on seasonal variability and dynamic range in soil moisture, which can be used as an indicator of the hydrologic response of a region and on the variability of drought at continental spatial and decadal time scales.