Climate Variation in the Sanjiang Plain Disturbed by Large Scale Reclamation during the Last 45 Years

Farmland instead of marsh wetland has become the main landscape in the Sanjiang Plain after large scale reclamation since 1949. The underlying surface of the Sanjiang Plain has been changed tremendously. Based on the data of monthly mean air temperature, atmospheric pressure, monthly precipitation and sunshine time from 21 meteorological stations in the Sanjiang Plain from 1955 to 1999, the climatic variations and tendencies of the Sanjiang Plain have been analyzed during the last 45 years. The climate jumps have been examined in terms of 5 year moving averaged seasonal and annual series of 4 factors using Yamamoto method and Mann Kendall method. The annual mean temperature was tending to go up and increased +1 2℃ to +2 3℃ in the Sanjiang Plain during the last 45 years. The warmest center was located in the plain field of the Sanjiang Plain. The departure values of annual mean temperature have been positive since 1988. The liner tendency values of annual precipitation in most part of the Sanjiang Plain were negative during the last 45 years. The decrease center in annual precipitation was located in the plain part of the Sanjiang Plain. The largest decrease amplitude of annual precipitation was 90 mm during the last 45 years. The variation of annual precipitation in the Sanjiang Plain during the last 45 years had gone through two increase periods that occurred from 1955 to 1965 and from 1980 to 1999. Between them there was a decrease period from 1966 to 1979. Climate jumps tested by both Yamamoto method and Mann Kendall method in the Sanjiang Plain during the last 45 years are as follows. According to the annual mean temperature, an abrupt warming occurred in the mid 1980s, the amplitude of abrupt variation was +0 9℃. The seasonal abrupt warming in spring, autumn and winter all took place in the 1980s, and abrupt warming in summer occurred in the late 1970s. Of variation amplitude of all the seasonal abrupt warming, the largest one was +1 8℃ in winter since 1987. The abrupt change of summer precipitation occurred in the 1980s. The abrupt changes of spring and winter sunshine time took place in the late 1980s and the early 1980s respectively. Based on the facts of climate changes of the Sanjiang Plain, it is held that the abrupt warming of the Sanjiang Plain during the last 45 years probably resulted from the large scale reclamation of various kinds of wetlands.