Hydrological implications of agricultural expansion on natural and degraded lands in Northeastern Brazil

Unplanned agricultural expansion puts pressure on natural ecosystems and harms water resources. In Brazil, agricultural growth continues to threaten natural ecosystems despite the availability of extensive degraded areas. This study examines the hydrological impacts of agricultural expansion using modelling under two land use and land cover (LULC) change scenarios in the Maxaranguape watershed, in Northeastern Brazil: an Optimistic scenario (S1), where agriculture replaces degraded pasturelands, and a Business-as-usual scenario (S2), where expansion encroaches upon natural vegetation. We projected agricultural expansion through 2034 based on the trend observed between 2000 and 2020, which showed an average increase of 5.8 km² per year. The Business-as-Usual scenario (S2) resulted in more pronounced hydrological impacts: surface runoff increased by 11.8 % in S1 and 13.2 % in S2, while groundwater flow decreased by 0.6 % and 1.1 %, respectively. These changes led to reductions in minimum streamflow (Qmin) of up to 2.4 % in S1 and 5.2 % in S2, and increases in maximum streamflow (Qmax) of up to 4.4 % in S1 and 2.7 % in S2. The greater decline in Qmin under S2 highlights a more severe impact on water availability—an especially critical concern in drought-prone regions like Northeastern Brazil. These findings underscore the importance of prioritizing agricultural expansion over degraded pasturelands rather than natural ecosystems, as this approach helps prevent further deforestation while promoting long-term water security.