Spatial estimation of standardized precipitation index based drought severity across Türkiye using machine learning models

Reliable spatial estimation of extreme drought intensity represented by the minimum SPI value is essential for water resources management under increasing climate variability. However, conventional assessments often rely on station-based temporal indices, providing limited representation of spatial heterogeneity and topographic controls. This study developed a machine learning framework to estimate the spatial distribution of extreme drought intensity represented by the minimum SPI value across Türkiye using long-term precipitation records from 102 meteorological stations. For each station and SPI accumulation period, extreme drought intensity was represented by the minimum (most negative) SPI value observed over the 1935–2024 record; this minimum SPI value was used as the machine-learning target, while latitude, longitude, and elevation were used as geographic predictors. Seven machine learning models were evaluated; among them, GBM yielded the highest accuracy (R 2 = 0.991, RMSE = 0.007), followed by XGBoost and CatBoost. These results indicate that ensemble tree-based methods reproduce the observed spatial pattern of extreme drought intensity across the station network with high accuracy; establishing predictive skill at unmonitored locations would require evaluation under a station-grouped partition. Furthermore, feature importance and SHAP analyses showed that spatial predictors (longitude, latitude, and elevation) were substantially more influential than the time-scale variable, although their relative importance varied among the evaluated models. This framework offers a robust tool for interpretable and spatially explicit drought monitoring in topographically complex regions.