Abstract: Climate change is acknowledged as one of the most critical problem that human being has ever been faced,which has a complex impact on water resource.With the overwhelming emphasis on developing the time series variation characteristics of water resource,based on the meteorological data of meteorological administration from 1951 to 2009,this paper estimated potential evapotranspiration(E) and difference of precipitation and evaporation(W) by the Penman-Monteith model of Food and Agriculture Organization(FAO) nominated in 1998 and analyzed evolution characteristics of precipitation(P),E and W in Erhai Lake Basin.The result showed that annual precipitation varied in different decades with a decreased and then increased trend in the recent 59 years.Meanwhile,annual spring precipitation varied in different years with an increased trend,with a linear trend value of 13.6 mm per 10 years.Annual summer precipitation had a same trend in different decades.Moreover,autumn precipitation had a "less-more-less" trend in general.The result of Mann-Kendall analysis indicated that the mainly two time point mutation were 1995 and 2005,in which year annual precipitation showed a mutation from less to more in Erhai Lake Basin.Meanwhile,spring,summer and winter precipitation showed a remarkable mutation,not as in autumn.The result also showed that annual and autumn evaporation varied in different years with a decreased trend in the recent 59 years,with a linear trend value of 6.8 mm per 10 years and 3.0 mm per 10 years respectively.In addition,the evaporation of three other seasons had a fluctuation change and varied with a significant decreased trend in last several years.The evaporation of Mann-Kendall analysis indicated that the mutation occurred in different years and that the period of less evaporation continued in last several years.The seasonal distribution of precipitation,and available water resources was not in accordance with the monthly distribution.Simultaneously,the seasonal distribution of evaporation showed an approximate parabola with a max value in May.The risks of the future droughts for spring,autumn and winter in this region still existed,which will restrict the development of garlic for winter and corn in slop land.

Key words: Precipitation, Evapotranspiration, Difference of precipitation and evapotranspiration, Mutation analysis