Understanding flash drought variations in China's planted and natural forests through machine learning counterfactual analysis

China’s rapid forestation over the past decades has reshaped regional ecohydrology and raised concerns of intensifying drought. Here, we explore the historical drought variations and driving factors across China’s planted and natural forests using multi-source satellite observations from 1990 to 2024. Results indicate that planted forests experienced more frequent flash droughts (7.05 vs. 5.76 per 5 years) with shorter duration (35.08 vs. 36.12 days) and faster recovery (14.81 vs. 15.94 days) than natural forests. Regionally, the contrast between planted and natural forests is most notable in the mid-temperate semi-humid zone and the Tibetan Plateau temperate zone. A bidirectional gated recurrent unit (Bi-GRU) modeling framework coupled with paired-stand matching and counterfactual analysis was established to isolate climatic and forest-feature impacts on flash drought and slow drought risks. Although climate remains the dominant factor in forest drought risk, counterfactual analysis holding climatic conditions constant revealed that intrinsic forest attributes also contributed, manifesting as a 12% lower slow drought risk yet a 7% higher flash drought risk in the paired planted forests. Moreover, results of the Shapley Additive Explanations (SHAP) attribution further shows that while increased precipitation more effectively mitigates flash drought in planted forests, these forests simultaneously display heightened sensitivity to vapor pressure deficit. Furthermore, forest attributes (e.g., normalized difference vegetation index, leaf area index (LAI), canopy height) show a stronger contribution to the modeled flash drought risk in planted forests than natural forests. Our results underscore a tradeoff that planted forests are less exposed to prolonged slow drought but comparatively more prone to rapid-onset flash drought. Such asymmetry calls for region-specific density control and species mixing strategies for forest management to sustain ecosystem resilience. • Within a climate-dominated regime planted forests had more frequent flash droughts. • Counterfactuals demonstrate that forest attributes also contribute to drought risk. • Increased precipitation more effectively alleviates flash drought in planted forests.