Optimizing the Master Recession Curve for Watershed Characterization and Drought Preparedness in Eastern Cape, South Africa

Regions grappling with water scarcity are compelled to fortify their hydrological analytical protocols for efficacious drought disaster preparedness, considering the escalating influence of climate change on river periodicity and the sustainable management of water resources. Hence, this study presents a novel optimization and standardization approach for master recession curve (MRC) parameterization to improve the existing MRC computation for environmental flow (EF) parameterization. The study framework is based on constructing MRC using the RECESS computational tool. The concept involved normalizing quadratic improvement in the digitally filtered, smoothed, and automatically extracted MRC parameters from 24 long-term winter streamflows (2001–2020) in South Africa. The optimum recession length suitable for MRC computation obtained was ten days based on the significant proportion of the variance in streamflow as a function of flow timing (R2 > 0.935), EF consistency in most watersheds (p-value < 0.00), optimum standard error, and the appreciable years of significant discharge. The study obtained the MRC index, EF threshold, and the probable diminution period of 3.81–73.2, 0.001–20.19 m3/s, and 3.78 to 334 days based on the periods of significant discharge ranging between 4 and 20 years, respectively. The concurrent agreement of rainfall trend and baseflow (p-value < 0.05) with MRC parameters validate their performance as tools for EF conservation. The intra-variation in MRC across the 24 stations alluded to the overriding influence of river aquifer connectivity on watershed viability. The study provides profound insight into perennial and ephemeral rivers’ viability/vulnerability, indispensable for watershed prioritization, policy formulation, early warning systems, and drought preparedness.