Trends of Precipitation and Air Temperature in Northern California under SRES Scenarios

In this study, recent precipitation trends based on CCSM3-based MM5 simulations were investigated against PRISM-based precipitation for 11 years from water year 2000 to water year 2010 for 8 watersheds in Northern California. Six precipitation projections (A1B1, A2, B1, A1FI, Ensemble1 and Ensemble2) were used for this study. In general, the case of Ensemble2 shows the most realistic trends against PRISM precipitation, especially for last 5 years, and is similar to PRISM in total volume of precipitation for 11 years. However, the case of A1FI also shows the realistic trends in mountainous watersheds (UFRW, ARW and YBW). It means that the precipitation under A1FI scenario is also important for future climate change impact study. Less precipitation was found under A1B and A1FI scenarios and more precipitation was found under A2 scenario. Although precipitation under B1 scenario is realistic compared to other scenarios (A1B, A2 and A1FI), the most realistic scenario is Ensemble2 (ensemble average of 4 scenarios). However, it was found that the precipitation difference against PRISM precipitation is locally different for all scenarios. Through the analyses for the extreme precipitation between the control run for 20th century and the projections for 21st century under CCSM3 gas emission scenarios, the extreme precipitation not only under A1B, A2 and B1 but also under A1FI scenario was much frequently found than historical period. It means that the A1FI scenario is also important to assess the future climate change impacts not only for water resources but also extreme floods.