A Study On Some Problems Of The Climate Change Of Global Land Precipitation For June-August During 1948-2001

Based on the global land monthly rain data (PREC/L) created by Chen et al (2001), NCEP/NCAR reanalyzed monthly mean wind data and global monthly SST grid data edited by British Meteorological Bureau, this paper investigates some problems of the climate change of global land rainfall for June-August(JJA) during 1948-2001. The main contents and results are as follows.The distributive feature of global land rainfall for JJA during 1948-2001 is analyzed. One can see that the maximum precipitation occurs in the monsoon areas, and their standard deviation is bigger in monsoon areas than the others . The distribution of the rainfall is continuous along the latitude belts.The study on the time series of global land average seasonal precipitation points out that the interannual and interdecadal fluctuations of the rainfall are clear. The late 1940s-late 1960s and the 1980s-1990s corresponds to wet period and dry period respectively, and the 1970s expresses a apparent interannual variation of rainfall. The significant decrease of rainfall began in the late of 1970s. The time series contains the obvious 2-7 years cycle in consistence with the ENSO cycle as well as the decadal cycle.The spatial distribution feature of rainfall trend for global land seasonal and monthly rainfall indicates that the rainfall in global land areas is characterized by the negative trend variation. In the last 54 years, seasonal and monthly rainfall of the global land and the Northern Hemisphere have a marked decreasing trend. But for the rainfall of the Southern Hemisphere, the negative trend is not apparent. Seasonal rainfall for six large-scale areas all show negative trend. It's found that the negative trend of precipitation in Africa is the most significant, and next come Eurasia and Australia, rainfall in North America, South America and Antarctic is not apparent minus-trend. The rainfall of six latitude belts expresses a decreasing feature. The negative trend of the rainfall in tropical areas is the most significant, but it isn't apparent in the high-latitude of the two hemispheres.The paper identifies the drought and flood years for precipitation during JJA in Global land, Northern Hemisphere, Southern Hemisphere and six continent areas respectively, and make statistic tests. The results suggest that the connection is close between drought (flood) years and warm (cold) events in global-scale areas. The distribution of drought and flood years in global land takes on a decadal feature as well as in the Northern Hemisphere, Southern Hemisphere and six large-scale areas.Finally, the relations between rainfall in global land during JJA and wind fields, SST and ENSO are discussed. The results show that drought or flood in global land and large-scale areas correspond to the singularity of wind well in the same term. In addition, the global rainfall is coherent with SST to a certain degree. ENSO has a significant impact on global rainfall. To most of areas in global land, the average precipitation in El Nino years are less than that of it in La Nina years.