Pan evaporation in the Shiyang River basin increased over 1961-2005, except in the middle reaches where it decreased. The biggest rise was in winter. Factors like humidity and temperature influenced the changes, with humidity being most important in spring, summer, and autumn, and temperature in winter. The upper reaches were affected by humidity and temperature, the middle reaches by diurnal temperature range, and the lower reaches by humidity and precipitation. Overall, humidity had the most impact on pan evaporation in the basin.