Research on the Detail Time of Grassland Water Deficit for the Qinghai-Tibetan Plateau

The detail variations of precipitation, potential evapotranspiration (PET) impacts the terrestrial ecosystem.The grassland water deficit or surplus status (GWDS) from 1961 to 2010 were systemically studied for the Qinghai-Tibetan Plateau (QTP) using daily data of all meteorological stations. The results indicated that the temporal variations of precipitation were not corresponding to those of PET in a year. The maximum monthly precipitation occurred in July, while the maximum monthly PET appeared in June, the spring precipitation was ranked the second, but its PET was ranked the first in a year. The total water deficit (PET-precipitation) from March to June was more, 51.4 % of the total annual value. Therefore, the drought more frequently occurred in Spring and June in the QTP. The grassland can be protected in a year, especially in Spring and June.