Assessing monthly rainfall and runoff trends for sustainable water resource management in lower Shoalhaven river

Abstract

Abstract The hydrological extremes, floods and droughts are reducing the reliability of water supplies worldwide. Understanding the local seasonal variability of hydroclimate is needed to manage such extremes. This study examines monthly rainfall and runoff trends in the lower Shoalhaven River catchment, a critical area for Sydney's water supply. We employed the Mann–Kendall test and Sen’s Slope estimator to detect changes in hydrological patterns. The analysis revealed significant increasing rainfall trends in February (0.38 mm/year) and November (0.27 mm/year) and a significant decreasing trend in July (0.25 mm/year), from 1884 to 2023. Despite these variations in rainfall, runoff data from the two primary gauge stations did not exhibit statistically significant trends from 1992 to 2023 and 1988 to 2023, respectively, indicating stability in runoff patterns. This stability is likely due to the regulatory influence of the Tallowa Dam, which moderates flow variations downstream. The study highlights the potential benefits of implementing adaptive management strategies, including developing coastal reservoirs, to enhance water storage capacity and mitigate flood risks. These strategies could complement existing infrastructure by capturing excess runoff during high rainfall and ensuring water availability during dry periods. Further research is recommended to explore the interactions between rainfall, runoff, and other environmental factors, as well as the feasibility of integrating coastal reservoirs into the Shoalhaven River catchment's water management system.