Drastic changes of long-term precipitation trends from pre-monsoon to monsoon season in Asia during the past 45 years (1961-2005)

Time-space characteristics of long-term trends of precipitation patterns in Asian monsoon region have been examined using the 45 years (1961-2005) digitized monthly precipitation data from the Global Precipitation Climatology Center (GPCC) (Schneider et al., 2008). We have found an interesting feature of seasonal change of spatial patterns in linear trends of monthly precipitation anomalies. Figure 1 shows the spatial pattern of trends in pre-monsoon or early monsoon months of May (left) and mature monsoon months (June/July/August). A contrastive change of trends from May to the monsoon months (JJA) is noticeable particularly in northern India and China. That is, increasing (decreasing) trends are dominated in India (China) in May but these features are totally reversed in the monsoon season (JJA). Another remarkable feature is the overall increasing trends over the Tibetan Plateau both in pre-monsoon and monsoon periods. The dynamics relevant to these seasonally-dependent drastic changes of the trend patterns are being studied, by using a high-resolution aerosol-chemistry climate model, considering the anthropogenic forcings (e.g., increase of greenhouse gases and aerosol changes), in addition to the long-term natural-forcings (e.g., regional to global scale sea surface temperature anomalies). References: Schneider, U., T. Fuchs, A. Meyer-Christoffer, B. Rudolf (2008) Global Precipitation Analysis Products of the GPCC.