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The upper reach of the Yangtze River, 4 511 km long from west to east, contains a great amount of water resources of the Yangtze River Basin. This article studies the characteristics of the pan evaporation, the related meteorological variables, and their effects on the pan evaporation, based on the data of the daily pan evaporation (1980-2008) and other meteorological variables (1961-2008). The results show that the linear trend of the pan evaporation has remarkable regional features, i.e., the decrease trend in the southwest and the increase trend in the northeast of the investigated region, and the Yangtze River is approximately the boundary of these trends. The meteorological variables have different effects on the pan evaporation depending on the fact that they are in the category the thermal variables or the dynamic variables. The thermal meteorological variables (i.e., air temperature, diurnal temperature range, and sunshine duration) have positive partial correlations with the pan evaporation, while the dynamic ones (air pressure, rainfall, and relateive humidity) have negative correlations with the pan evaporation. The correlation of the wind speed remains to be investigated.

Evaporation plays an important role in water balance on the land surface. In Northern China, the evaporation series of the recent 115 years was reconstructed on the basis of Thornthwaite evaporation formula. The characteristics of the reconstructed series were analyzed using 10-year running mean filter, power spectrum method, and running t-text of abrupt changes on the paper. The results showed that there were remarkable interannual fluctuations with timescales of about quasi-8-year, 3-4-year, and quasi-2-year, and interdecadal oscillations with timescales of 57.5-year, quasi-23-year, and 11.5-year. Meanwhile, the abrupt changes of the evaporation series were also of interdecadal timescale. Either interannual fluctuations or interdecadal oscillations of evaporation were closely related to variations in air temperatures and precipitation.