Impact assessment of vegetation cover changes on the water regulation service in the Onzaga River watershed

Watersheds play a fundamental role in the hydrological cycle because of their contributions to the water regulation of essential tributaries for ecosystems. However, the balance between soil and climatological components of these watersheds has been altered by human activities, which directly impacts them through changes in land use. In Colombia, the lack of control over land-use in watersheds has affected the water regulation services of important tributaries, such as the Onzaga River, whose waters are mainly used for agricultural activities. For this reason, this study aims to evaluate how changes in land use in the basin affected the capacity of water regulation. For this, a statistical correlation analysis was conducted between the Water Regulation Index (WRI) and vegetation cover areas from 1985 to 2023. The study results indicate that the expansion of the anthropogenic vegetation covers, such as agriculture parches and grasslands, replacing different types of forests, and producing an adverse effect on the water regulation capacity for the basin. This demonstrated its decrease along with an increase in its variability, indicating that, in addition to its degradation, there is a greater irregularity in this ecosystem service. In conclusion, correlation analysis indicates that 93% of the change in water regulation regime is explained by the contraction of forest cover and the expansion of agricultural areas, degraded lands, and urban development. This study confirms the importance of preserving native vegetation cover in the watershed, especially in areas adjacent to watercourses with riparian forests.