Attributing the changes in evapotranspiration and its components to climatic factors and vegetation dynamics in the Three-River Headwaters Region.

Abstract

The Three-River-Source National Park serves as a critical ecological barrier, and investigating its evapotranspiration mechanisms is of great significance for regional ecological protection and maintaining ecosystem stability. This study focuses on the Three-River Headwaters Region (TRHR), simulating and analyzing the spatiotemporal evolution patterns of ET (evapotranspiration) and its components (Canopy transpiration (ETC), Interception evaporation (ETI), Soil evaporation (ETS)) from 2000 to 2020 based on the PT-JPL model. Partial correlation analysis, multiple regression analysis, random forest modeling, and PC-Momentary Conditional Independence (PCMCI) analysis were employed to explore the associations of climatic factors and vegetation dynamics with ET and its components. The results indicate: (1) From 2000 to 2020, ET in the TRHR exhibited a significant decreasing trend (p < 0.001), with high values in the east and south and low values in the west and north, along with pronounced spatial heterogeneity in trend patterns across different areas. (2) Meteorological variables exhibited a warming-and-drying tendency with enhanced energy availability, characterized by significant increases in temperature (Temp) and radiation (Rad), rising Vapor Pressure Deficit (VPD), and a slight but spatially heterogeneous increase in precipitation (Pre). (3) Vegetation significantly improved (Leaf Area Index, LAI generally increased), but its impact on ET components showed a "dual effect": LAI had an extremely significant negative correlation with ETC (areas with negative partial correlation accounted for 90.68%), while showing an extremely significant positive correlation with ETI (85.95%). (4) The random forest model indicated that LAI is the most important driving factor for ET changes. (5) VPD primarily inhibited ETC and ETI, while Temp and wind speed (WS) promoted them. (6) PCMCI results indicated a significant lagged negative association of Temp with ET and its components. These findings are significant for constructing water resource-sustainable ecological restoration strategies under observed climatic variability and vegetation change.