Quickflow (QF) is the fraction of rainfall that rapidly runs off to channels, a key element for understanding floods and designing control measures. It reflects rapid runoff pathways that drive peak flows, sediment pulses, water-quality downstream impacts, and hazards. QF is influenced by the precipitation regime (seasonality and event concentration) and by surface properties represented by land use/land cover (LULC) and soil types, which modulate infiltration and storage. We applied the InVEST–Seasonal Water Yield (SWY) model at 30 m resolution in the San Fernando–Soto la Marina basin. We used monthly climate, 2020 LULC, and soil type data, and analyzed (i) the basin-wide distribution of QF, (ii) the spatial influence of LULC- and soil-based on QF, and (iii) the precipitation–QF relationship. Results show a multimodal distribution of QF ratios; urban areas, bare soils, and low-cover croplands yield higher QF than woody covers; and the precipitation–QF relationship is positive but dispersed, modulated by the sequence and intensity of events and by surface conditions. We conclude that integrated land and water management should (a) focus on targeted interventions in high-QF zones that maintain or improve vegetation cover and promote infiltration to reduce flooding and erosion and promote increased dry season flows and (b) integrate improved temporal and spatial representation of precipitation events with realistic LULC and soil parameterizations for more accurate model outputs and reliable planning.