Analyzing Potential Evapotranspiration and Climate Drivers in China

Abstract

AbstractPotential evaporation is a function of several climatic factors including humidity, wind, air temperature and solar radiation. It is shown that potential evaporation decreased in eastern China, southwest China, and regions south of the Yangtze River from 1980 to 2000 while potential evaporation increased significantly in two geographic regions of China (the middle reaches of the Yangtze River to the Great Bend of the Yellow River and Northeast China) over the same time period. It is proposed that this increase in potential evaporation is due to an increase in air temperature. These evaporation trends were obtained using Empirical Orthogonal Function (EOF) analysis of 20 cm dish meteorological station data from 1980~2000. Since incident solar radiation levels (the amount of solar radiation striking a surface per unit of time and area) in China have declined since the 1970s, potential evaporation is not primarily dependent on solar radiation. It is proposed that two factors contribute to the observed irregular distribution of potential evaporation. First, wind speed analysis and saturation vapor pressure field results (based on the vapor pressure deficit) suggest that the dynamic effect of the atmosphere contributes to potential evaporation. Second, remotely sensed 1980~2000 NOAA‐AVHRR data shows that vegetation degradation in many regions of China are highly correlated with thermal and physical land surface changes.