Deep scars of fire: A conundrum of shrinking forests, biological invasions, and dryness leading to lower water provision and security

Fires represent a powerful force, impacting biogeochemical cycles and processes inherent to terrestrial and aquatic interfaces, jeopardizing ecosystem services crucial for wildlife and livelihoods. In the Serra do Rola Moça State Park, southeastern Brazil, a complex of springs supplies water to the sixth largest Brazilian metropolis, Belo Horizonte. Fires are common in this park in the dry season , spanning across the grassy matrix formed by the following ecosystems: open grassland ( campo sujo ), savanna (Cerrado stricto sensu ), quarztitic campo rupestre (quartzitic rupestrian grassland), ferruginous campo rupestre (ironstone rupestrian grassland), and gallery forests. Using remote sensing techniques, we mapped the region’s vegetation cover for 1973 (the first year with high-quality satellite images available) and compared it to the cover in 1994 (when the park was established), and in 2023 (the most recent data). These data indicated a 40 % loss of forest cover and an expansion of grassland-savanna formations over the past 50 years. Using logistic regression, we showed that forest fires were the main cause for forest loss. We used the Soil and Water Assessment Tool (SWAT) model to simulate and compare water balances in the 1970 s and current scenario (2023), and to estimate threats to urban supply. The simulations pointed to an increase of ∼ 25 % in surface runoff and annual losses of ∼ 18 % in the volume of water infiltrated into the soil. As the areas burned were negatively correlated with the amount of rainfall, the persistence of fires, linked to extended periods of drought, undermines the water yield from sources within this region that contribute to urban water supplies . Our data suggest that the high frequency of wildfires is driving this critical water security region toward collapse, posing significant risks to ecosystem functioning. This collapse could result in future water shortages and an increased risk of flooding during extreme rainfall events.