We will present the results from hydroclimate studies for the southwestern U.S. during the 1997-1998 winter season using the Regional Climate System Model (RCSM). This study is focused on a diagnosis and prediction of the seasonal hydroclimate of the southwestern U.S. for an application to flood forecasting and water resources assessment.
Regional hydroclimate has major impacts on the occurrence of natural disasters, the amount of available water resources and the health of local ecosystems. In the southwestern U.S., increasing industrial activities and the expansion of urban areas into steep hillsides and flood planes have enhanced the impacts of the hydroclimate on human lives and local economies. The southwestern U.S. hydroclimate is characterized by wet winters and dry summers, where the effects of complex terrain on precipitation, surface energy budget and streamflow partly determines snowcover and water supply during summertime. Extreme seasonal bias in precipitation makes it important to efficiently maintain and operate water storage facilities. Complex terrain causes local heavy precipitation and rapid streamflow response that can cause severe flood damage. Long-term climate change may affect the timing of snowmelt which in turn affects summertime water supply and snowmelt-driven spring floods within mountainous areas. Therefore, accurate assessments and predictions of hydroclimate is important for efficient water resources management, reduction of flood damages and long-term development and conservation planning.
The RCSM has been successfully applied to studies of the seasonal hydroclimate, weather, quantitative precipitation, and streamflow forecasts, and water resources for the western U.S. region. The RCSM again showed a good skill in simulating precipitation and basin-scale hydroclimate of the 1997-1998 winter season. A seasonal hydroclimate prediction study was started from the last winter as a collaboration with the NCEP and the University of California institutions. For the extreme El Niņo winter of 1997-1998, our seasonal hydroclimate prediction experiment has produced an encouraging results.