Spatial-temporal change analysis of evapotranspiration in the Heihe River Basin

Evapotranspiration (ET) is one important component of hydrological process. It is also a limited factor for ecological environment conservation. The unreasonable utilization of water resources resulted in many problems in the Heihe River Basin, such as the over exploited of water resources, especial the ground water, the river flow decrease, land degradation. A correct understanding of the water consumption characteristics is undoubtedly a base of achieving the sustainable development of society, economy, and improving the eco-environment. In this paper, the time series of ET data estimated by ETWatch model which had been validated for different landscapes during the period of 2000-2010, were analyzed in spatial and temporal scales. The deviation of annual ET estimated by ETWatch with the observation ET data from eddy covariance system (EC) in the four observation stations of the basin was in the range of 5-8%. The conversion of land use type had a great impact on total water consumption across the basin due to lower variance of ET for three vegetation types. Base on the correlation analysis of climate factors and ET, there were apparent impact on ET in the upstream and midstream, but not in the downstream because of complicated human activities. The significant relations between temperature and ET (R=0.842~0.941), and between precipitation and ET (R=0.582~0.840), indicated that these two climate parameters were key influence factors on ET for grass land; The soil water storage was likely another influence factor on ET for the forest besides the temperature which had close relations with ET (R²=0.617~0.822). The spatial-temporal change analysis of ET and driven factors can be contributed to better understanding the eco-hydrological effect of the specific forest in Qilian Mountains.