Assessing future climate changes and extreme indicators in east and south Asia using the RegCM4 regional climate model

This paper assesses future climate changes over East and South Asia using a regional climate model (RegCM4) with a 50 km spatial resolution. To evaluate the model performance, RegCM4 is driven with "perfect boundary forcing" from the reanalysis data during 1970-1999 to simulate the present day climate. The model performs well in reproducing not only the mean climate and seasonality but also most of the chosen indicators of climate extremes. Future climate changes are evaluated based on two experiments driven with boundary forcing from the European-Hamburg general climate model (ECHAM5), one for the present (1970-1999) and one for the SRES A1B future scenario (2070-2099). The model predicts an annual temperature increase of about 3A degrees-5A degrees (smaller over the ocean and larger over the land), and an increase of annual precipitation over most of China north of 30A degrees N and a decrease or little change in the rest of China, India and Indochina. For temperature-related extreme indicators in the future, the model predicts a generally longer growing season, more hot days in summer, and less frost days in winter. For precipitation-related extremes, the number of days with more than 10 mm of rainfall is predicted to increase north of 30A degrees N and decrease in the south, and the maximum five-day rainfall amount and daily intensity will increase across the whole model domain. In addition, the maximum number of consecutive dry days is predicted to increase over most of the model domain, south of 40A degrees N. Most of the Yangtze River Basin in China stands out as "hotspots" of extreme precipitation changes, with the strongest increases of daily rain intensity, maximum five-day rain amount, and the number of consecutive dry days, suggesting increased risks of both floods and droughts.