Study on the change of annual potential evapotranspiration in the Tianshan Mountainous in resent 36 years and its comparison with that in South Xinjiang and North Xinjiang.

Based on the climatic data observed by 24 meteorological stations in the different climatic regions of Xinjiang during the period of 1971-2006,in this paper the potential evapotranspiration at all the stations are calculated with the Penman-Monteith equation recommended by FAO in 1998,and the change characteristics of potential evapotranspiration in the Tianshan Mountains are compared with that in South Xinjiang and North Xinjiang.The results are mainly as follows:(1) The change trend of potential evapotranspiration in the Tianshan Mountains is similar to that in South Xinjiang and North Xinjiang,but the average value and the linear degression speed of potential evapotranspiration in the Tianshan Mountain are lower and the annual and decadal change is more stable than that in South Xinjiang and North Xinjiang;(2) The cyclical change of annual potential evapotranspiration in the Tianshan Mountains is similar to that in North Xinjiang,and there is a remarkable cycle about 4.5 years,but there is no remarkable cycle less than 36 years in South Xinjiang in recent 36 years;(3) A sudden reduction of potential evapotranspiration occurred in the Tianshan Mountains in 1991,it occurred in South Xinjiang and North Xinjiang in 1988 and 1986 respectively,and it was 3~5 years latter in the Tianshan Mountains than that in South Xinjiang and North Xinjiang;(4) The main spatial distribution characteristics of annual potential evapotranspiration are the synchronous changes in these three regions,but the synchronous change of spatial distribution of annual potential evapotranspiration is the highest in North Xinjiang and the lowest in the Tianshan mountains.The reverse change in the spatial distribution of annual potential evapotranspiration is the highest in the South Xinjiang and the lowest in the Tianshan Mountains;(5) Spatiotemporal difference of climate change is the main factor causing the different change of potential evapotranspiration in different regions.Under the background of reduction of potential evapotranspiration in recent 36 years,wind speed increased,but the precipitation and air relative humidity decreased in the mid-and late-1990s.