Global Trends in Drought Impacts on Wildlife-A Review

Drought is expected to increase in frequency and severity due to climate change, highlighting the urgency of understanding drought impacts on wildlife across geographies and taxonomic groups. We conducted a review of peer-reviewed articles from 1982 to 2024, focusing on the impacts of anomalous drought on terrestrial vertebrates. We recorded 3324 total wildlife responses, 188 from single-species studies and 3136 from multi-species studies. Within single-species studies, 66% of responses were negative, 32% were unclear, and 2% were positive, illustrating the widespread threat of increasing drought to global wildlife. Within multi-species studies, 24% of responses were negative, and 5% were positive. Notably, 71% of responses within multi-species papers were categorized as "unclear", highlighting the need for additional investigation and the complexity of synthesizing a diverse literature. Drought impacts are not evenly tested across taxa, with birds being the most frequently studied (51% of documented responses), followed by mammals (28%), amphibians (16%), and reptiles (5%). Geographically, studies tended to occur most often where recent increases in anomalous drought have been observed (e.g., the Southwestern United States, South Africa, and Southeastern Australia). The sophistication of how drought is measured has increased over time, whereby studies increasingly defined drought as an anomalous event in comparison to a long-term average through the use of drought indices, rather than as a short-term weather event. However, we did not see consistency in indices used across the literature, which has the potential to present challenges for interpretation and synthesis. This review summarizes the predominantly negative impacts of drought on terrestrial vertebrates and the growing challenge of conserving wildlife in a changing world, while also highlighting gaps in our understanding of drought-wildlife relationships that can guide future research.