Nonlinear Responses and Spatial Heterogeneity of Net Ecosystem Productivity to Extreme Weather Events in Central Asia

The increasing frequency and intensity of extreme weather are profoundly affecting the ecological carbon cycle in arid regions, yet there remains a lack of quantitative understanding regarding the nonlinear response of net ecosystem productivity (NEP) in Central Asia to changes in extreme weather conditions. This study focused on the five Central Asian countries and China’s Xinjiang region, where NEP was estimated using MODIS Net Primary Productivity and daily meteorological data, and 12 extreme climate indices (ECIs) were constructed. By combining the XGBoost model with the SHapley Additive exPlanations method, the key ECIs of NEP were identified for different regions, and their nonlinear responses and threshold characteristics were quantified. The results show that from 2000 to 2023, Central Asia overall acted as a weak carbon source, with NEP exhibiting a spatial pattern of increasing in the east and decreasing in the west. Extreme precipitation indices showed an overall declining trend, whereas extreme temperature indices increased significantly. There is significant spatial heterogeneity in the importance of ECIs across different regions. Specifically, the annual total precipitation (PRCPTOT) is most important in Kazakhstan, Kyrgyzstan, and Tajikistan, while the annual maximum of daily maximum temperature (TXx) shows greater importance in Turkmenistan and Xinjiang. The responses of NEP to ECIs exhibited significant nonlinear threshold characteristics. PRCPTOT showed a positive saturation effect in Kazakhstan, Kyrgyzstan, and Tajikistan, with a threshold range of 700–1000 mm in Kyrgyzstan. TXx exhibited a pronounced negative high-temperature effect in Turkmenistan and Xinjiang, with thresholds of approximately 42 °C and 30 °C, respectively. In Uzbekistan, Diurnal Temperature Range (DTR) showed a response trough near 10 °C. The study reveals the nonlinear response and spatial heterogeneity of the NEP in Central Asia to extreme weather change, offering theoretical support for ecosystem restoration and sustainable carbon management in arid regions.