An Analysis Of Changes Of Precipitation Over Asia,1951-2009

Atmospheric precipitation is one of the key components of terrestrial watercycle. Complex terrain and sea-land distribution characteristics in Asia make aremarkable regional difference in precipitation and extreme precipitation events.In order to detect and understand the response of regional terrestrial water cycleto global warming, it is important to analyze the temporal and spatial variationsof daily precipitation in continental or sub-continental scales in modern times. Inthis paper, the daily and monthly precipitation data from the US National ClimateData Center for period1951-2009are used to analyze the long-term variations inprecipitation over Asia. The preliminary quality control for the daily data is done, and a dataset of619stations is setup for East Asia, while only571stations inAsia are used for the monthly data. The regional average time series are obtainedby a method of area-weighted average for the grids. The spatial and temporalpatterns of long-term changes in modern times in all kinds of precipitation eventsare analyzed. Special effort is given to the investigation of East Asian region dueto the good quality of data. The main conclusions are summarized as follows:(1) For climatological feature, terrain factors have played a decisive role onthe different spatial precipitation distribution in Asia. The west part of Asia has arelatively even precipitation in different seasons, while in most other parts of Asia,summer precipitation is the largest and winter precipitation is the least.In East Asia, the amount, frequency and intensity of annual averageprecipitation, including all seasons and all levels, generally increase from thenorthwest to the southeast. The start time of rainy season shift to an earlier date,and the end time of rainy season are delayed. The duration time of rainy season increases. The percentage of the rainy season precipitation increases. In thewestern parts of the Honshu and Hokkaido islands in Japan, many precipitationindices, including annual average rain days, autumn and winter rainfall, low-levelprecipitation and the duration of the rainy season, are significantly larger thanthose in other regions of East Asia.(2) The long-term change in precipitation in Asia is not obvious.Precipitation generally decreases in the west and east part of Asia, and increasesin the central part of Asia. The regionally consistent precipitation change is notfound, but for the eastern part of Asia, the precipitation increases almost in all ofthe stations north of the40degree, and it decreases in most of the stations in thesouth.The regional average precipitation and precipitation intensity decrease overthe last59years in East Asia, while the rainy days exhibit no significant trend. Inmost of North China, eastern Mongolia, southern part of the Russian Far East and most parts of Japan, the amount, frequency and intensity of annual precipitationgenerally decrease. However, the southern part of Middle Siberia, the KoreanPeninsula and the Yangtze basin witness increasing trends of the indices series ofprecipitation. The distribution of rainy days has the tendency of centralization.No-rain days and continuous rain events both witness upward trends.(3) In most parts of Asia, seasonal difference in precipitation generallystrengthens, and the seasonal distribution of precipitation sees a discretizationtrend. The trend in East Asia is opposite, however, and the seasonal precipitationvariability within the year in the latest decades tends to be gentler than before.Regional average of start and end time of rainy season are significantly earlier,and the duration of the rainy season is significantly reduced.(4) The regional average precipitation decreases in East Asia for all of thecategories for time period1951-2009. The moderate precipitation amountdecreases faster than the precipitation frequency, but the intense and very intense precipitation amount decreases a little bit slower than the precipitation frequency.Moderate, intense and very intense precipitation frequencies all decrease duringthe last59years, and only the light precipitation frequency experiences anincreasing trend. It is also interesting to note that, for the last30years(1980-2009), the overall precipitation intensity decreases while the overallprecipitation frequency increases for most areas in East Asia. The precipitation istending to be less extreme in terms of daily precipitation intensity.