Climate Change and Hydrologic Modeling

Climate changes due to increased concentration of greenhouse gases (GHGs) have obvious effects on the regional landscape systems, water cycles, and particularly catchment hydrology. Changes in hydrologic cycle will affect almost every aspects of socioeconomic life, from agricultural production and energy consumption to flood control, municipal and industrial water supply, conservation of natural resources, and ecohydrological management. Some parts of the world may experience increases in precipitation and some may experience decreases. The timing and frequencies of storm events may alter in some areas, and some regions may experience the increased potential for evapotranspiration. Because of close interactions between water, socioeconomic activities, and cultural practices, climate change impact on regional water availability is considered one of the most important impacts of future climatic changes on society. Therefore, a reliable estimation of stream flows is required for water resources planning, design, and management in a changing climate. A fundamental problem is the fact that the spatial and time scales of global climate models (GCMs) and hydrological models are extensively different. As a result, downscaling of climate model outputs is essential. Assessment of uncertainty in the simulated outputs of climate downscaling technique and in the predicted stream flows is also necessary before their application to climate change impact studies. Selection of climate predictors in downscaling studies and selection of an appropriate hydrologic model are critical issues in climate change impact studies. This chapter provides the details of climate models, their downscaling techniques, selection of appropriate hydrologic models, and uncertainty analysis, and delineates recommendations for climate change impact studies on water resources.