Spatio-temporal change characteristics of pan evaporation and possible climate factors in the Gongga Mountain under changing environment

摘要

To grasp the spatio-temporal change characteristics of the amount of pan evaporation and possible climate factors in the Gongga Mountain located at the southeastern fringe of the Qinghai-Tibet Plateau, we performed an analysis over a period of 22 years, from 1988 to 2009, in two different altitude zones (1600 m a.s.l and 3000 m a.s.1), based on the methods of Mann-Kendall non parametric, climatic trend rate and complete correlation coefficient. The result indicated that: (1) there were significant decreasing trends of Epan in the annual changes in two sites. Different decreasing trends of Epan were observed in different altitude sites, the annual decreasing tendency of Epan in GGF (3000 m a.s.l) was significant at the 0.01 significance level and the decreasing rate was 160 mm/10years. However, the decreasing tendency in GGS (1600 m a.s.1) was significant at the 0.05 significance level and the annual decreasing rate was 396 mm/10 years. (2) In GGF, the seasonal decreasing tendencies were significant at the 0.01 significance level except in the autumn, while the decreasing tendencies were significant at the 0.05 significance level in the GGS area. The seasonal variety trends in GGS were different from the GGF. In GGF, the decreasing trend of Epan was largest in the spring and remained more-or-less constant in the autumn. In GGS, the largest decreasing rate was in the winter and the smallest in the summer; (3) Correlation analysis found that the ground temperature, minimum ground temperature, sun duration, precipitation, relative humidity and wind speed have the correlation with the Epan. The trends analysis show that the annual range of ground temperature, minimum ground temperature, precipitation, and relative humidity was increased, while sun duration and wind speed decreased. (4) As well as the effect of minimum ground temperature, decreasing in both sunshine duration and wind speed were the main influencing factors leading to the decrease of pan evaporation in both altitude zones based on the methods of regression and complete correlation coefficients analysis. Precipitation factors were also important impact factors on pan evaporation in the GGS area.