Seasonal hydrologic dynamics under changing climate, land use-land cover and human influence

Climatic changes along with the land use-land cover changes (LULCC) and human impacts significantly modify the hydrologic flow regime of the river basins, affecting water resources and environment from regional to global scale. Aided by satellite data, modeling and understanding of the interactions between physical and human systems, more reliable regional LULCC and climate change projections are now available. However, resulting quantitative projection of changes on the hydrologic components at the seasonal time scale are sparse. This study attempts to quantify the hydrologic response in different hydro-climatic regions of the world at the seasonal time scale in the context of the projected LULCC and climate change assessed through Intergovernmental Panel on Climate Change (IPCC) A1B emission scenario. The Common Land Model (CLM) is used as the hydrologic model for the study since it incorporates detailed physical process representation, uses physical parameterization without the need for calibration and can be run at relatively high spatial and temporal resolutions. A coupled modeling framework is applied to assess human water use impact on hydrologic discharge at the river basin scale by coupling of CLM to the Water Availability and Supply Model (WASM).;A consistent global GIS based dataset is constructed for the Surface Boundary Conditions (SBCs) and meteorological forcing of the model. European Center for Medium Range Weather Forecasts (ECMWF) reanalysis data at 6-hour time step for the period 1976 through 2000 is used for meteorological forcing. The model results are validated using the observed discharge data from Global Runoff Distribution Center (GRDC). The ability of the hydrologic model to capture the dominant runoff processes at multiple time scales of interaction of the processes is explored using wavelet analysis. Future climate change projections are derived from the Fourth Assessment Report of IPCC based on the multi-model ensembles of projections. An Integrated Model to Assess the Global Environment (IMAGE), developed by the Netherlands Environmental Assessment Agency is used for LULCC data.;The study is performed over nine river basins selected from Asia, Africa and North America to represent the broad climatic, landscape and human controls on the seasonal hydrological dynamics, and to assess how these controls differ for basins lying in different hydro-climatic regions. It is observed for all the study basins that small changes in the precipitation lead to much larger changes in the runoff response. The analysis reveals that certain regions (Orange and Volta basins in Africa) have seasons which are highly likely to experience significant reduction in future runoff while there are other regions (Ganges, Krishna and Huai basins in Asia) which have seasons very likely to experience increased runoff. These seasonal differences reflect the changes in water availability, which may not be known through annual estimates. Moreover, different aspects of human interferences are observed over each of the study basins. Comparison and quantification of such differences in the hydrologic components are of particular importance for the water resource managers and policy makers.