New research shows that declining rainfall heightens encounters between people and wildlife, especially carnivores, revealing how drought reshapes ecological and human behaviour across California.
Study: Human-wildlife conflict is amplified during periods of drought. Image Credit: JoeFotos / Shutterstock
In a recent study published in the journal Science Advances, researchers examined the influence of drought on human-wildlife conflict. Interactions between humans and wildlife have become more prevalent, representing a fundamental challenge for conservation programs. As antagonistic human-wildlife interactions persist, a deeper understanding of how climate change affects resource availability and human-wildlife conflict dynamics is crucial for characterizing future changes in socioecological systems.
How Drought Alters Wildlife Resource Use
Drought is a common manifestation of climate change that strains both wildlife and human populations. While drought may limit resource availability for wildlife in wildlands, human infrastructure often buffers its effects, attracting wildlife to anthropogenic subsidies. As such, opportunities for human-wildlife conflict can intensify due to increased overlap and competition for shared resources. However, the precise behavioral and ecological mechanisms linking drought to increased conflict remain uncertain, and the study emphasizes that these associations do not establish causation because they reflect correlations rather than demonstrated behavioral shifts.
Data Sources for Analyzing Conflict Trends
In the present study, researchers investigated the effects of drought on human-wildlife conflict. They leveraged the Wildlife Incident Reporting (WIR) database of the California Department of Fish and Wildlife, which comprises human-wildlife incident reports from 2017 to 2023. Reported incidents encompass a wide range of interactions within four main categories: depredation, general nuisance, potential human conflict, and sightings.
“Climate change will increase human-wildlife interactions, and as droughts and wildfires become more extreme, we have to plan ways to coexist with wildlife,” said lead author Kendall Calhoun, a member of Justine Smith’s lab at UC Davis and of UCLA’s Tingley lab on ecology and conservation. “Animals coming into human spaces are generally framed as wildlife trying to take resources from humans, but it’s often because we’ve taken the resources away from the wild areas.”
Incident Categories Linked to Conflict Severity
The team primarily focused on two categories most likely associated with negative interactions, general nuisance, and depredation. The state of California was divided into 50 km by 50 km grid cells for analysis, and reported conflicts within each cell and month were compared with environmental covariates. Environmental covariates included seasonality (month), precipitation, human population density, median household income, and habitat structure (tree cover).
Modeling Drought Effects With Bayesian Methods
A hierarchical Bayesian modeling framework was adopted to investigate how changes in precipitation and other covariates affect incident frequency. In one model, incident reports for all species were treated agnostically and modeled together. Further, a separate set of diet-specific models was developed to explore whether these effects varied by species and diet guilds, where species were modeled under a shared diet-group hyperparameter.
Comparing Environmental Drivers Across Conflict Types
The influence of each environmental covariate on the frequency of conflict reporting across the four categories was also compared. In addition, three models investigated species-specific responses and the impact of diet on trends in reported conflicts, one for each diet group: carnivores, herbivores, and omnivores. In these species analyses, reports of species with more than 40 reported conflicts were included. The authors also noted that reporting patterns are partly shaped by human behavior and perceptions, which may influence how often conflicts are reported rather than how frequently they actually occur, because shifts in human activity, visibility, and willingness to report can contribute to observed trends.
Drought-Linked Conflict Increases Across California
The WIR database comprised 31,904 incident reports in California between 2017 and 2023. Most reports (57.2%) were related to depredation. The researchers found a significant increase in the number of wildlife conflicts associated with reductions in precipitation. Every 25 mm decrease in annual precipitation increased the frequency of reported incidents by 2.11%.
Habitat and Socioeconomic Factors Intensifying Conflict
Further, higher tree cover, higher human population density, and higher median household income, as well as areas with both higher human population density and tree cover, were associated with increased conflict reporting. Independently, depredation, general nuisance, and potential human conflict were negatively associated with precipitation. Notably, reported incidents showed the highest increase with decreased precipitation for carnivores.
Carnivore Sensitivity to Drought-Driven Resource Shortages
Importantly, decreased precipitation was a strong predictor of conflict reporting for carnivores, but not for herbivores or omnivores at the diet-guild level, clarifying that the earlier effects for carnivores remained robust at the species level rather than the guild-level aggregate. Species-specific analyses revealed significant increases in reported conflicts, accompanied by reduced precipitation, for three carnivores (mountain lions, bobcats, and coyotes) and one omnivore (American black bears). This distinction highlights that drought sensitivity is strongest for particular species rather than all members of a diet group.
Species-Level Conflict Rates Under Drought Stress
The number of conflicts increased for every 25 mm reduction in precipitation by 2.97 percent for bobcats, 2.56 percent for American black bears, 2.21 percent for coyotes, and 2.11 percent for mountain lions. Finally, the team investigated whether the frequency of conflict reporting varied with intra-annual drought periods and found that trends in reported incidents sharply increased during the driest and warmest months of the year (May to October) for eight species. These seasonal increases occurred independently of year-to-year precipitation trends, reflecting both ecological and human behavioral patterns, such as greater outdoor activity and higher wildlife detectability during summer months, as well as reduced water availability during peak drought periods.
Conservation Implications of Climate-Enhanced Conflict
Taken together, the results underscore that climate change may have significant ramifications for the future of conservation and human-wildlife conflict. The finding that lower precipitation is associated with conflict warrants investigations into how exactly drought affects space use and behavior for human and wildlife communities. The results also showed that carnivores experienced nearly three times the effect of drought as herbivores.
Seasonal Drought Patterns Shaping Conflict Risk
Further, season was a robust determinant of conflict reporting, and this effect is likely replicable in regions where intra-annual water availability influences human-wildlife interactions. While the impact of ongoing droughts may perturb animal behavior year-round, their effects are likely to be most pronounced when precipitation is at its seasonal low. The study also emphasizes that reporting patterns may be influenced by socioeconomic factors, cultural norms, and willingness to report conflicts, suggesting that the observed increases may reflect both ecological responses and human behavioral changes during drought conditions, including shifts in recreation timing, resource use, and opportunities for human-wildlife encounters. Overall, the study provides crucial empirical evidence on the amplification of human-wildlife conflict by climate change.
“I look at ways to improve human-wildlife interactions, and climate change is going to make that path more difficult,” Calhoun said. “But if we can make it worse, then we can make it better. People just need to be invested in their local environment to make conservation work.”
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