As human populations continue to expand, negative interactions with wild animals are becoming more common. These can jeopardize people’s safety and livelihoods, and often end in the animals’ deaths through retaliatory killing. Because of this, human-wildlife conflict presents a major challenge for conservation efforts.

At the same time, climate change is predicted to alter the distribution of people, wildlife, and resources. This could mean an increase in conflict if wild animals are driven toward human-controlled resources.

The current study investigated the effects of climate change on human-wildlife conflict, focusing on California, a drought-prone U.S. state. Drought is a common manifestation of climate change, and can draw animals into human-populated areas in search of food and water. The researchers collected statewide annual precipitation data and human-wildlife conflict reports between 2017 and 2023. These reports fell into four broad categories, but the study focused on the two types most directly associated with negative interactions: depredation (18,190 reports) and general nuisance (4,799 reports). Depredation refers to predation on farmed animals and other kinds of property damage, while general nuisance includes incidents not associated with property damage.

The main analysis examined how precipitation levels influenced negative interactions between humans and wild animals over the seven-year study period. The researchers predicted that because they have specialized diets, carnivores and herbivores would be more sensitive to the effects of drought and therefore involved in more conflict than omnivores, whose diets are more flexible.

A total of 63 species were identified in the conflict reports. The top 10 most-reported included (in descending order):

• American black bears
• Wild pigs
• Mountain lions
• Coyotes
• American beavers
• Bobcats
• Wild turkeys
• Mule deer
• Raccoons
• Gray squirrels

Across all species, the total number of reported incidents increased by around 2% for every 25-millimeter (one-inch) decrease in annual precipitation. Annual precipitation values across the state ranged from close to six to just over 4,000 millimeters. Lower precipitation was associated with more conflict reporting. However, it didn’t affect neutral reporting, such as simple sightings of wild animals. Taken together, this suggests that drought led to more conflict, not just more interactions.

There were also clear seasonal trends as conflict reports increased during the driest months of the year — May to October — for eight of the 15 species with the highest number of reported incidents.

Decreased precipitation had a much stronger influence on conflict reporting for carnivores than for herbivores or omnivores. Mountain lions, coyotes, and bobcats were particularly impacted. However, reported incidents with one omnivorous animal, the American black bear, increased significantly as precipitation decreased. According to the researchers, these results show that conflict between humans and carnivores is more sensitive to drought, though they note that species identity is likely more important than broad dietary categories for understanding how animals will respond to climate change.

The results speak to a connection between human-wildlife conflict and animal agriculture, which isn’t explored in this research but should be given careful attention when advocating for animals harmed by conflict. The effect of drought on carnivores in this study was nearly three times stronger than for herbivores. Predators are often stigmatized as a threat to human safety and livelihoods, and may be removed by lethal means wherever in the world they coincide with people. The study suggests that climate change, and drought in particular, may worsen these tensions.

These patterns of conflict likely also apply to seasonality, not just to drought-prone regions. Climate change may lengthen dry summers and shorten wet winters in Mediterranean climate ecosystems, extending periods of heightened conflict.

It’s important to highlight that the conflict report data may not represent the full scale of incidents in the region. People vary in their willingness to report based on factors such as their perceptions of wildlife and state agencies. For instance, farmers may have an incentive to report if they’re compensated for losses caused by conflict. Despite these limitations, the researchers remain confident that the dataset is large enough to see clear reporting trends.

Additionally, the study used precipitation data as a representation for drought, which limits the conclusions to shorter-term variations in precipitation levels. The effects of multi-year droughts may be more complicated.

Promoting coexistence strategies will have great value in lessening conflict — for example, by providing alternative water sources or other resources tailored toward species particularly prone to conflict. However, as this research demonstrates, conflict mitigation alone might not be enough. The results also underscore the importance of advocacy for climate action in ensuring the long-term safety and well-being of both humans and wild animals.