Soil Moisture–Drought Nexus across Brazil: Identifying Current Issues and Future Perspectives

Droughts impact ecosystem activity, water security, and energy production. Recent studies have advanced the understanding of current drought periods and projected expectations for these events in a future of climate change. However, the relationship between droughts and soil moisture (SM)—a key variable in global ecology—remains poorly understood. Therefore, addressing the soil moisture–drought nexus is crucial for water and natural resources management. This endeavor may be particularly challenging in tropical regions like Brazil, a continental-scale country that harbors extensive biodiversity. To bridge this gap, we conducted a state-of-the-art review investigating the soil moisture–drought nexus across Brazil under current and future scenarios. The review findings indicate that SM behavior varies between different Brazilian biomes and regions under water scarcity. Nevertheless, a strong seasonality in SM was detected, suggesting the intensification of drought events in both current and future conditions. Furthermore, several Brazilian crops may become vulnerable in a drier climate, highlighting the urgent need to optimize water use in agriculture while maintaining crop productivity. Given the challenge of water scarcity, it is also essential to adopt strategies that balance agricultural land use with the conservation of natural vegetation, as these often intersect. Based on assessments of the soil moisture–drought nexus with methods ranging from remote sensing products to ground-based data, we concluded that national-scale analyses are valuable for decision-making and resource provision, while field investigations improve the understanding of the physical mechanisms behind land-atmosphere interactions. Our conclusions underscore the necessity of considering soil moisture as an independent variable in future studies, rather than relying on proxies, as it plays a unique role within the climatological and hydrological systems. We believe that the findings of this review can help improve soil water management under drought conditions not only in Brazil but also in Earth’s tropical zone as a whole.