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Xu Guochang (Lanzhou Institute of Arid Meteorology,Lanzhou\ 730020) Yao Hui\ Li Shan (Meteorological Bureau of Gansu Province,Lanzhou\ 730020)  
In this paper,we made a comparative study on the present climate change in arid and semi-arid regions of China.We used data from 135 stations in northwest China,together with data from 160 stations run by National Meteorology Center,and the runoff data in arid regions.In order to divide regions objectively,the fuzzy cluster method was used.In each fuzzy cluster region,temperature representative stations were chosen in the countryside with minimal urban effect,and a largern umber of precipitation representative stations were chosen.Temperature data cover 61 years:1935~1995,and precipitation 59 years:1932~1990.In order to show principal climate fluctuation more clearly,tendency analyses and moving average method were used. It is shown that,in most part of the arid and semi-arid regions of China,1930s and 1940s were the warmest periods during the last 60 years.In winter,from the late 1940s up to the early 1950s,temperature dropped rapidly,1960s being the coldest decade.After this,warming followed.From 1980s to the early 1990s,temperature has been above the mean but much more lower than 1930s~1940s.In summer,after 1930s~1940s high temperature period,a cooling spell persisted until the middle of 1980s,1980s being the coldest decade,i.e.20 years later than that in winter.After this,there was as low warming.How ever until the early 1990s,it was still below the mean. The general trend of temperature variations in arid and semi-arid regions of China were consistent with that of entire China,but its amplitude was larger.For the high temperature interval in 1930s~1940s,the former was much more distinct than the later. Temperature variations in arid and semi-arid regions of China were somewhat different from those in Northern Hemisphere.For example,while the former experienced a rapid cooling in 1940s~1950s the later only had amoderate drop in 1960s~1970s in temperature.During the last 10 years,slight warming was observed in the former but marked warming occurred in the later.It should be noted that the present day summer temperature is much lower than the mean in the arid and semi arid regions of China.There is also a differnece in tempearture variations between winter and summer.However,in northern Xinjiang and Qinghai tempaerature showed a rising trend during the last 40 years,which was compatible with that in north and northeast China.There was an 8 year periodicity in the temperautre variation for the arid and semi arid regions of China. Precipitation in semi arid regions of China showed decreasng trend during the last 40 years,particularly in northwest China.This decreasing trend was observed in the eastern part of Hexi Corridor,Qilianshan Mountains and Qinghai.In the eastern part of northwest China,there was a marked quasi 3 year periodicity.But in the north China a quasi 35 year periodicity was noticable.By contrast,precipitaiton in arid regions of China showed a marked increasing trend during the last 40 years. Water resources of the arid regions originate form the surrounding mountains.Since the glaciers supply runoff ratio is less than 25%,for the Tianshan Mountains and the Qilianshan Mountains the runoff chage may reflect in change precipitation in the mountains.Totao runoff in northern Xinjiang showed some decade fluctuations;a show increase from 1910s through 1960s,a decrease in 1960s~1970s and an increase afterwards.The runoff chage in the middle of the Qilianshan Mountains was similar to those in northern Xinjiang.In the west part of the Qilianshan Mountains,Kunlunshan Mountains and Karakorumshan Mountains runoff increased during 1950s~1980s.Only in the eastern part of the Qilianshan Mountains,it decreased during the sam eperiod.Therefore,for most mountains precipitation and runoff increased during the last ten years,which was similar to the change in arid regions.Since,in Kunlunshan Mountains and Karakorumshan Mountains,glaciers supply runoff ratio was higher,glacier melt was of importance to the runoff increase. It is interesting that the maximum precipitation increase between 1961~1990 and 1931~1960 was
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