The lag and cumulative response of water use efficiency to the climate on the Shiyang River Basin, Northwest of China

Water use efficiency (WUE), as an indicator for plants to regulate water physiological processes through photosynthesis, is a key link between carbon and water cycling in ecosystems, reflecting the rapid adaptation strategies of vegetation ecosystems to site environment and resource changes. In this study, satellite data and ground-based observation data from 2001–2020 were developed to simulate and estimate the spatial distribution characteristics of WUE in different functional zones and analyze the time lag and cumulative effects of climate on vegetation. The results show that: (1) In the past 20 years, the spatial distribution of WUE in the SRB showed a south-high, north-low, with high-value areas primarily in the southern part of Zone I, Zone II, the Changning Oasis and Jinchuan in Zone Ⅲ, and the Hexi Bao Oasis. Temporal analysis within the SRB indicated a decreasing trend in WUE across different ecological functional zones, notably most significant in ZonesⅢ. (2) The annual WUE of vegetation in the SRB exhibited a negative correlation with temperature, with large areas showing positive correlations in January-March, May, and September-December, and negative correlations in April and June-August. In contrast, the relationship between WUE and precipitation was consistently negative, with the strongest negative correlation observed in June. (3) In the SRB ecological functional Zones I-IV, the monthly WUE showed similar lagged and cumulative effects of temperature (TLA0-0) as the overall basin, while the effects of precipitation featured a three-month cumulative lag (TLA0-3).