Utilizing Solar-Induced Chlorophyll Fluorescence for Drought Monitoring and Net Ecosystem Productivity Response in Northwest China

Against the backdrop of global change, frequent and severe droughts pose major threats to ecosystems, and quantifying ecosystem anomalies driven by hydrothermal stress remains challenging. Based on this, we propose a drought-monitoring framework centered on solar-induced chlorophyll fluorescence (SIF) and develop an SIF-based Vegetation Health Index (SHI) to improve monitoring performance. Compared with existing SIF-based drought indices (e.g., TFDI and TSWDI), SHI provides a more direct representation of photosynthetic stress, making it more suitable for elucidating drought-response mechanisms. In addition, we use net ecosystem productivity (NEP) to represent carbon sequestration and apply multiple correlation analyses to investigate NEP responses to drought and their spatiotemporal differentiation across vegetation types. Results indicate an overall wetting trend in the study region during 2001–2024, and SIF-based indices perform better in characterizing drought and vegetation responses. The dominant coupling scale between NEP and drought is annual, with an overall lag of 0–3 months: croplands show the strongest coherence and the shortest lag (0–1 month), grasslands are intermediate, and forests show longer lags (2–5 months) as well as a more persistent response window. This study highlights SHI’s advantages for drought monitoring and carbon sink diagnostics, supporting differentiated drought mitigation and management in NWC.