Spatial and temporal distribution characteristics of reference evapotranspiration trends in Karst area: a case study in Guizhou Province, China

Reference evapotranspiration (ET0) is the essential part of hydrological cycle and crop irrigation system (watering system framework). To reveal the change pattern of annual and seasonal ET0 and its corresponding dominated factors aspects of karst regions in China, daily meteorological data of 19 meteorological stations during 1959-2011 in Guizhou Province were collected. ET0 trends in seasonal and annual time series were detected by nonparametric Mann-Kendall test. The results indicated (demonstrated) that the annual ET0 for the entire Guizhou Province performed a decreasing trend by 0.4476 mm/year. The seasonal ET0 in spring and summer performed the an alike decreasing trend, while it presented an increasing trend in autumn and winter. According to the rotated empirical orthogonal function clustering method, Guizhou Province was divided into four parts. Annual ET0 performed (executed) the ascendant trend in western area, while the descendent trend occurred in middle, northwestern, and southwestern areas. The sensitivity and the attribution analysis indicated (specified) that the relative humidity was identified as the most sensitive variable to the annual ET0 and sunshine duration as the essential main thrusts for the declined annual ET0 in Guizhou Province. In addition, the more severe of karst landform development, the more obvious decreasing trend in ET0.