Spatiotemporal variation of water cycle components in Minjiang River Basin based on a correction method for evapotranspiration products

Study region: Minjiang River Basin of China. Study focus: This paper aimed to study the spatiotemporal changes in water cycle components including evapotranspiration (ET) and terrestrial water storage in a watershed. To achieve this, we proposed a method that is based on the water balance and utilizes measured annual precipitation and runoff data to correct ET products. Subsequently, we derived the annual terrestrial water storage changes and performed trend analysis on the water cycle components by the MannKendall trend test. New hydrological insights for the region: (1) The Global Land Data Assimilation System (GLDAS) product overestimated ET from 2000 to 2019 in the Minjiang River Basin (MJB), which was 105.18 mm higher than ET. Through sub-basin validation, the relative error between the corrected ET and the ET is less than 5.1%. The proposed method can construct a reasonable annual dataset of water cycle components. (2) From 2000-2019, the Minjiang River Basin witnessed nonsignificant increasing trends in precipitation and runoff. However, significant growth was observed in ET, indicated by a Mann-Kendall trend test Z-value of 2.63. The variation in ET was primarily influenced by the normalized difference vegetation index (NDVI) (correlation coefficients of 0.37) and temperature (correlation coefficients of 0.48). The terrestrial water storage change fluctuated between - 400 and 355 mm. The relationships among the water cycle components, as represented by the runoff coefficient and evapotranspiration coefficient show nonsignificant changing trends. Both displayed a non-significant decreasing trend. From 2000-2019, the water cycle process remained relatively stable under changing environments in the MJB.