Association between drought-related indices and the Number of Deaths in the Desert Adjacent Areas of Western China: A Time Series Study Based on Ecological Vulnerability Assessment

Objective: To conduct an ecological vulnerability assessment in the ecologically fragile Hexi region of western China, providing a reference basis for promoting the health of residents in ecologically vulnerable areas. Methods: In Wuwei City, located within China's Hexi Corridor and characterized by its proximity to desert regions, an ecological vulnerability evaluation system has been developed employing the Sensitivity-Resilience-Pressure (SRP) model. The Analytic Hierarchy Process-Principal Component Analysis Entropy Weight Combination Model (AHP-PCA) was then applied to analyze the Ecological Vulnerability Comprehensive Index (EVSI) of Wuwei City from 2014 to 2023, followed by classification using the natural breakpoint method. Based on the ecological vulnerability classification, the distributed lag nonlinear model (DLNM) was employed to examine the impact of drought-related indicators (Standardized Precipitation Index (SPI) and temperature-humidity index (THI) ) at each level on population mortality, calculating the cumulative relative risk (CRR). Finally, the synergy index was used to evaluate potential interactions between SPI and THI in impacting mortality rates. Results: (1) An ecological vulnerability assessment index system for Wuwei City was constructed using 13 natural and socio-environmental variables, categorizing ecological vulnerability into highly vulnerable (EVSI > 3.814), moderately vulnerable (2.927 < EVSI ≤ 3.814), and low vulnerability (EVSI ≤ 2.927). (2)The differences in mortality rates among high, medium and low ecologically fragile areas in Wuwei City were statistically significant. (3) Across all ecological vulnerability levels, SPI in moderately vulnerable areas showed the highest cumulative effect on mortality at lag 0 days and cumulative lag 14 days, with CRRs of 1.10 (95% CI: 1.07–1.14) and 1.10 (95% CI: 1.06–1.14), respectively. In low-vulnerability areas, the cumulative effect on mortality was highest when the THI reached 23 on the same day (CRR=1.16, 95% CI: 1.13–1.18), and also when the cumulative THI reached 60 after 21 days (CRR=1.16, 95% CI: 1.11–1.21). Conclusion: The mortality rate of the population varies in different areas with fragile ecological environments, and there is a correlation between ecological environment vulnerability and the risk of population death.In highly ecologically fragile environments, the risk of mortality increases due to extreme drought, with effects persisting longer. When ecological conditions are favorable at low fragility levels, the impact of THI on mortality becomes more pronounced.