Cataloguing soil moisture droughts on a global scale since 1980

To describe droughts at the global scale, many variables can be employed to express their extent, duration, severity or dynamics. To identify common features of global land drought events (GLDEs) based on soil moisture modelling, we prepared a robust method for their delimitation and classification (cataloguing). Estimates of root-zone soil moisture from the SoilClim model and the mesoscale Hydrologic Model (mHM) were calculated over global land from 1980–2023. Using the 10th and 20th percentile thresholds of soil moisture anomalies, outputs of the two models were merged into a united dataset of drought affected areas in a 10-day step with 0.1° resolution. OPTICS clustering of the gridded data was then used to identify a total of 736 GLDEs. By utilizing four spatiotemporal and three motion-related characteristics for each GLDE, we established threshold percentiles based on their distributions. This information enabled us to categorize droughts into seven severity categories and seven dynamic categories. The severity and dynamic categories overlapped substantially for extremely severe and extremely dynamic droughts but very little for less severe/dynamic categories, despite some very small droughts that have occasionally been very dynamic. The frequency of GLDEs has generally increased in recent decades across different drought categories but the increase is not always statistically significant. Overall, the cataloging of GLDEs presents a unique opportunity to analyze the evolving features of spatiotemporally connected drought events in recent decades and provides a basis for future investigations of the drivers and impacts of dynamically evolving drought events.