Spatial and temporal variation patterns of eferenceevapotranspiration across the Qinghai-TibetanPlateau during 1971-2004

摘要

Reference evapotranspiration (RET), an indicator of atmospheric evaporatingcapability over a hypothetical reference surface, was calculated using the Penman-Monteith method for 75 stations across the Qinghai-Tibetan Plateau between 1971 and2004. Generally, both annual and seasonal RET decreased for most part of the plateauduring the study period. Multivariate linear models were used to determine thecontributions of climate factors to RET change, including air temperature, air humidity,solar radiation, and wind speed. Spatial differences in the causes of RET change weredetected by K-means clustering analysis. It indicates that wind speed predominated thechanges of RET almost throughout the year, especially in the north of the study region,whereas radiation was the leading factor in the southeast, especially during thesummertime. Although the recent warming trend over the plateau would have increasedRET, the combined effect of the reduced wind speed and shortened sunshine durationnegated the effect of rising temperature and caused RET to decrease in general. Thesignificant decrease in surface wind speed corresponded to the decreasing trends ofupper-air zonal wind and the decline of pressure gradient, possibly as a result of therecent warming.