[Spatiotemporal characteristics of reference crop evapotranspiration in inland river basins of Hexi region].

Based on the 1961-2008 daily observation data from 17 meteorological stations in the inland river basins in Hexi region, the daily reference crop evapotranspiration (ET0) in the basins was computed by Penman-Monteith equation, and the spatiotemporal characteristics of seasonal and annual ET0 were studied by GIS and IDW inverse-distance spatial interpolation. In 1961-2008, the mean annual ET0 (700-1330 mm) increased gradually from southeast to northwest across the basins. The high value of mean annual ET0 in Shule River basin and Heihe River basin declined significantly (P < 0.05), with the climatic trend rate ranged from -53 to -10 mm (10 a)(-1), while the low value of mean annual ET0 in Shiyang River basin ascended slightly. The ET0 in the basins had a significant annual fluctuation, which centralized in Linze and decreased toward northwest and southeast. The ET0 in summer and autumn contributed most of a year, and the highest value of ET0 all the year round always appeared in Shule River basin. The climatic trend rate was in the order of summer > spring > autumn > winter. Wind speed and maximum temperature were the primary factors affecting the ET0 in the basins. Furthermore, wind speed was the predominant factor of downward trend of ET0 in Shule and Heihe basins, while maximum temperature and sunshine hours played an important role in the upward trend of ET0 in Shiyang basin.