Variations and impact factors of potential evapotranspiration in karst area of Northwest Guangxi over the last 60 years

Based on climatic data of 7 meteorological stations in karst areas of northwest Guangxi from 1951 to 2011,Penman-Monteith equation was used to estimate monthly potential evaporation(ET0). Temporal and spatial variations of climatic variables and ET0 were then analyzed using statistical analysis. Contribution rate analysis was used to analyze the influence factors of ET0. The results showed that there was a warming trend in this region. Regional temperature had increased about 0.024-1.116℃ in the last 60 years. The annual mean temperature had increase 0.004-0.186℃/10a. In contrast, there were decrease trends for annual mean precipitation, wind speed, sunshine duration and relative humidity.Furthermore, relative humidity, net shortwave radiation and air temperature were the most sensitive factors. Seasonally,the highest sensitivity coefficients to air temperature and sunshine hours and the lowest sensitivity coefficients to wind speed are both in the summer. The absolute sensitivity coefficients to relative humidity are low in rainy season. The sunshine duration and wind speed impacted ET0 negatively trend and relative humidity and temperature impact ET0 positively. However, larger contribution from sunshine duration and wind speed cause ET0 to decline. Consequently, the change of ET0 was primarily attributed to the significant decrease in sunshine duration and wind speed.