Variation characteristics of the difference between evaporation and precipitation during grass growing season in Maqu County from 1971-2010

In order to study the variation characteristics of the difference between evaporation and precipitation during the grass growing season in Maqu County, the PenmanMonteith model was employed to compute the potential evapotranspiration based on the meteorological data from 1971 to 2010 in Maqu weather observation station. The results indicated that the difference between evaporation and precipitation in Maqu increased with the ratio of 12.1 mm10 a-1 during the grass growing season. The difference between evaporation and precipitation in the start and end period of growing season increased with the ratio of 3.5 and 11.2 mm10 a-1, respectively, whereas the difference decreased in the middle period of growing season with the ratio of -2.6 mm10 a-1. The water deficit occurred in the 1990s due to the increase of potential evapotranspiration and the decrease of precipitation. Water deficit was one of the most important impact factors for the grassland degradation and environmental deterioration in Maqu County.