Abstract
Geomorphology influences hydrologic response behavior of watersheds but seasonal responses such as dry season flow are rarely given focused more so their availability, quality, and spatiotemporal distribution. This is crucial for sustaining hydrologic ecosystem services (HES). This study assessed the influence of watershed morphometry on dry season flow volume and its selected physicochemical characteristics. Spot measurements of stream flow and its dissolved oxygen (DO), electric conductivity (EC), total dissolved solids (TDS), and Salinity levels from 56 small upstream watersheds in the Mts. Banahaw – San Cristobal Protected Landscape (MBSCPL) was determined. Principal Component Analysis (PCA) for variable reduction of geomorphological parameters and two-stage Random Forest Regression were used to determine the drivers of dry season flow occurrence and characteristics. Results showed that small upstream watersheds can exhibit sustained dry season flow with acceptable levels of EC, TDS, and Salinity. Total stream length (Tlu), Bifurcation ratio (Rb), area, and slope were the most important variables in predicting dry season flow volume, but its model showed poor validation performance and slightly overfit (R2= 0.527, p = 0.011). Models for water quality parameters showed acceptable performance for DO, EC, Salinity, and TDS levels (R2= 0.824, 0.713, 0.623, and 0.722, respectively) with flow volume (Q2018) as the most important driver, followed by Basin relief (Bh), watershed area, and slope.