An Analysis of Baseflow and Runoff Variability of Jamaican Watersheds

Understanding how Caribbean watersheds respond to climatic and landscape pressures is essential for
water-resource management in Small Island Developing States (SIDS). Jamaica’s rivers provide domestic
supply, irrigation, hydropower potential, and ecosystem services, yet limited work compares long-term
hydrological behavior across basins with contrasting geology, land cover, and rainfall regimes. This study
examines hydrological change in the Martha Brae, Rio Minho, and Rio Grande watersheds using daily
discharge (1981–2010) separated into baseflow and runoff with WETSPRO. Rainfall trends were assessed
using station data, and monotonic trends were quantified using the Mann–Kendall and Sen’s slope tests.
Dominant lithologies and land-cover classes were identified using geological maps and LULC datasets.

The results show clear divergence in hydrological trajectories across the three basins. In the
metamorphic–volcanic Rio Grande, baseflow increases weakly (τ = 0.0625; Sen’s slope = 2.03×10⁻⁴),
total flow shows a minimal rise (τ = 0.0182), and runoff slightly declines (τ = –0.0426). A significant
increase in rainfall (τ = 0.186, p = 0.021) indicates that rainfall is the main driver, with high forest cover
and permeable lithology promoting enhanced infiltration and groundwater recharge. In the karstic Martha
Brae, modest increases in total flow (τ = 0.065) and baseflow (τ = 0.0783; Sen’s slope = 5.45×10⁻⁵)
correspond with significantly rising rainfall (τ = 0.206, p = 0.012). Here, geology dominates, as the high
storage capacity of limestone aquifers regulates flow and buffers climatic variability. In the alluvial, semi-
arid Rio Minho, small increases in total flow (τ = 0.0801), runoff (τ = 0.0184), and baseflow (τ = 0.0940;
Sen’s slope = 3.64×10⁻⁵) occur despite no significant rainfall trend (τ = –0.025, p = 0.76), showing that
land cover and low-permeability sediments exert the strongest control by limiting infiltration and
sustaining weak baseflow.

These findings have critical implications for Jamaican water supply. Karst basins may continue to provide
reliable dry-season flows due to strong groundwater buffering, while alluvial, agriculturally disturbed
basins remain highly vulnerable to drought and flash-flood extremes. Strengthening forest cover,
protecting recharge zones, and improving land-management practices will be central to enhancing
Jamaica’s climate-resilient water-resource security.