Analysis of potential evapotranspiration in Heihe River Basin by GCM

Out of seven temperature-based potential evapotranspiration (PET) models, the Penman-Monteith model was selected for parameter correction in the Heihe River Basin. From climate output of CSIRO-Mk3.6.0, PET values were estimated for 1961-2015, 2021-2050 (T1) and 2051-2080 (T2), temporal and spatial variations were then analyzed. Hargreaves-Samani model with adjusted parameter value can be used in place of Penman-Monteith when meteorological data of the basin was absent (such as when temperature data only are available). Average PET was found to be 1 102 mm from 1960 to 2015, which increased from south (upstream) to north (downstream). Spatial distribution of average PET was unchanged in future periods, with PET reaches 1 622mm in T1, and 1 675mm in T2 period, 15% and 20% higher than historical period. Differences in PET changes were found among stations. Jiuquan station in the middle reach and Ejinaqi station in the lower reach decreased by 1.5% and 0.05% respectively; other stations increased by 1.4% - 20.9% for T1 period. For T2 period, all stations increased by 2.6% - 28.2%. The increases in PET in upper reach were greater than in lower reach for the two future periods.