Spatiotemporal Variation in Reference Evapotranspiration over Guanzhong Region and Its Determinants

Abstract

【Background and objective】 Evapotranspiration is an important component in the hydrological cycle in terrestrial ecosystems, and it is often calculated based on reference evapotranspiration (ET0) multiplied by a crop coefficient. In this paper, we analyzed the spatiotemporal variation of ET0 and its underlying determining factors in Guanzhong region. 【Method】 Daily meteorological data measured from 1980 to 2019 from 43 weather stations in the region were used to calculate ET0 using the Penman-Monteith model. Spatiotemporal change in ET0 and its underlying determinants were calculated using the inverse distance weight, stepwise regression analysis and path analysis. 【Result】 The maximum air temperature (Tmax), minimum air temperature (Tmin) and average air temperature (T) had been increasing at rates of 1.68~2.85 ℃, while the average relative humidity (RH) and wind speed (WS) had been declining in the studied period. In contrast, there was no noticeable change in sunshine hours (SSD). The meteorological factors varied spatially due to the difference in altitude and topography. The annual average ET0 from 1980 to 2019 was 959 mm, and had been increasing at a rate of 1.43 mm/a. Across the region, ET0 varied from 852~1 099 mm in 1980—2019, and decreased from the northeast to the southwest. In all regions, seasonal differences in ET0 were noticeable. The influence of meteorological factors on ET0 was ranked in the order of T>SSD>RH>WS. We also found that ET0 was positively correlated with SSD, T, and WS and negatively with RH. 【Conclusion】 Temporally, ET0 in Guanzhong region had been increasing from 1980—2019. Spatially, it decreased from the northeast to the southwest. The meteorological factors that affected ET0 most were T, SSD, RH and WS , in descending order.

Keywords

• reference evapotranspiration
• penman-monteith model
• inverse distance weight
• meteorological factor
• path analysis