Evaluating the Spatiotemporal Impacts of Ecological Water Conveyance on Riparian Vegetation Using an Eco-Hydrological Model Considering Time Lag and Cumulative Effects

Assessing the impact of ecological water conveyance (EWC) on riparian vegetation is crucial for the management of ecological hydrology in arid areas. This study proposed a random forest model that considers time lag and cumulative effects to simulate the spatiotemporal response of vegetation to EWC. By designing comparative models, the advantages of time lag and cumulative effects in elucidating the sustained impact of groundwater and meteorological factors on vegetation were demonstrated. The RF model was integrated with the MODFLOW model, resulting in an improved RF-MODFLOW model; this model outputs groundwater depth and vegetation spatiotemporal distribution data. The RF-MODFLOW model has the advantages of a clear physical mechanism and concise structural design. Applications downstream of the Tarim River Basin (DTRB) have shown that maintaining or increasing the existing EWC volume can ensure the stable recovery of vegetation coverage density and range. However, if the EWC volume were reduced by 30% due to water scarcity, the vegetation would experience significant degradation once again. This proves that the ecosystem in the DTRB is fragile and its sustainability highly depends on EWC. By calculating the coefficient of variation, it was demonstrated that the impact of EWC on riparian vegetation decreases with increasing distance from the river channel, with the maximum impact range between 2000 and 2500 m. The combination of the RF-MODFLOW model and scenario analysis could provide scientific support for managing EWC.