The Limits of Rain

Why Precipitation Alone Fails to Explain Shrubland Encroachment

Abstract

Namibia's savannas, a critical ecosystem for biodiversity, agriculture, and local livelihoods, are facing the escalating challenge of bush encroachment, particularly in the drylands of Otjozondjupa. This phenomenon, characterized by the unchecked growth of invasive brush species, significantly undermines the ecological balance and economic utility of the land, affecting ranchers, farmers, and wildlife. This study examines the role of precipitation in shrubland expansion across Otjozondjupa from 2014 to 2024 using Random Forest classification of Landsat 8 imagery and CHIRPS precipitation data. Results reveal no statistically significant correlation between annual, wet-season, or dry-season rainfall and shrubland persistence. While year-one precipitation failed to predict shrubland changes, a weak relationship emerged between year-two rainfall and shrubland expansion or loss mitigation. These findings suggest that precipitation alone is an insufficient predictor of encroachment. By highlighting the limitations of single-factor predictive analysis, this study underscores the importance of dynamic management strategies to identify key promoters of expansion and to effectively address shrubland encroachment in Namibia’s rangelands.