Nonlinear responses of ecosystem services to meteorological drought and driving factors analysis

Quantifying ecosystem service responses to meteorological drought is crucial for enhancing resilience in arid and semi-arid regions. Existing studies have largely focused on linear or static relationships with climatic factors, while lag effects, thresholds, and spatial heterogeneity remain underexplored. This study assessed four ecosystem services-water yield, carbon storage, soil conservation, and sand retention-in Inner Mongolia from 2000 to 2020. Multiple timescales of the standardized precipitation evapotranspiration index (SPEI) were employed to determine response times. Response thresholds were identified using constraint line analysis combined with generalized additive models, and driving mechanisms were examined with the XGBoost-SHAP model. The results showed that: (1) From 2000 to 2020, all four services improved overall, with the mean grid-cell values of water yield, sand retention, carbon storage, and soil conservation increasing by 1.29-, 7.86-, 0.15-, and 0.02-fold, respectively. (2) Drought-response timescales varied across services and aridity zones. Regionally, water yield, carbon storage, and soil conservation were most sensitive to 6-month SPEI, whereas sand retention responded to 24-month SPEI. Responses were uniformly rapid in semi-arid regions but diverged in arid regions, where sand retention responded rapidly while the other services showed longer lags. (3) The response threshold was defined as the dimensionless SPEI value at which an ecosystem service achieved its maximum potential supply; negative and positive values indicate drier and wetter conditions than the long-term average, respectively. Carbon storage, soil conservation, and water yield followed convex unimodal constraint patterns, while sand retention exhibited a hump-shaped response, with threshold values of −0.42, −0.13, 0.62, and 0.76, respectively. The threshold for sand retention decreased from 0.69 in semi-humid regions to 0.19 in semi-arid regions and − 0.02 in arid regions, suggesting a reduced moisture requirement for achieving maximum sand retention under increasingly arid conditions. (4) Precipitation, potential evapotranspiration, and wind speed were the dominant natural drivers of ecosystem service variation, while historical drought frequency and human activities, including ecological projects, grazing, and road disturbance, further modulated service supply. These results support zonal management tailored to individual ecosystem services by matching drought monitoring windows to response timescales, promoting vegetation restoration with low water demand and strong drought tolerance according to local moisture thresholds, and prioritizing the control of grazing and road disturbance in vulnerable transition zones.