The seasonal response of vegetation water use efficiency to temperature and precipitation in the Loess Plateau, China

Water use efficiency (WUE), which integrates ecosystem carbon and water cycles, is an important index for evaluating ecosystem sensitivity to climate change. Based on MODIS remote sensing data and meteorological data, this paper quantitatively studied the variation in seasonal vegetation WUE in the Loess Plateau over the period 2001–2019. Temperature and precipitation threshold effects on seasonal WUE of different vegetation types were also discovered using regression and partial correlation analysis methods. The results showed that seasonal WUE decreased with time in each season studied, with the rate of decrease of WUE in summer being the most significant of the three seasons studied. The following was the order of change in vegetation WUE values over time in different seasons: summer > autumn > spring. WUE of different vegetation types showed seasonal differences as well as varying responses to temperature and precipitation. The WUE of shrubland and grassland both tended to decrease over the study period from spring to autumn, with grassland WUE decreasing the most. When compared to grassland and shrubland, the negative relationship between forest WUE and the temperature was highest in spring and summer. The proportion of the area of vegetation where WUE was negatively correlated with temperature and precipitation in the three seasons, was largest in summer. In the relationship between seasonal WUE and either temperature or precipitation, there was a threshold effect. In spring, summer, and autumn, the optimum precipitation thresholds were 50–80 mm, 280–370 mm, and 65–125 mm, respectively, and the corresponding optimum temperature thresholds were > 14 °C, 15–19 °C, and 6–13 °C, respectively.