Study on Temporal and Spatial Variability of Pan Evaporation in Guangxi Province

Based on the measured data of 20 cm-diameter evaporation pan during 1957-2001 at 20 metrological observation stations in Guangxi Province,the inter-annual change characteristics of pan evaporation are analyzed using the coefficient of variation and extremum ratio.The cumulative filter method,Kendall test method and Mann-Kendall non-parameter statistics test method are used to investigate the change trend of pan evaporation and the change point.The results show that the annual pan evaporation was subject to dramatic change in Northern Guangxi,then that came second in Eastern and Southern Guangxi,and annual pan evaporation showed the minimal change in Central and Western Guangxi.There was no difference between the annual change of pan evaporation in the karst area and no-karst area.The pan evaporation of 10 percent of 20 metrological observation stations showed an increase trend,and 90 percent of that showed a decrease trend,furthermore,the pan evaporation of 72.2 percent among which displayed an obvious increase trend.The decrease of pan evaporation is mainly caused by the wind speed,cloud amount,and diurnal temperature range.Pan evaporation of 50 percent among the studied sites has significant change points.All the pan evaporation of 12 observation sites showed a decrease trend in Central,Eastern and Southern Province,and the change trend of pan evaporation was most obvious in Southern Province.There is no obvious difference between the change trends of pan evaporation in the karst area and no-karst area.