Content area
Full text
Introduction
Water stress affects many parts of the world, and it is also often a seasonal phenomenon, as exemplified by the seasonal variability in water availability [1]. The seasonal variability could be exacerbated by climate change, thereby reducing the reliability of the water supply [2]. Floods and droughts are the two main water-related disasters. Globally, the frequency and severity of floods and droughts are expected to increase further due to climate change [1]. To manage these risks effectively and ensure a stable water supply, it is critical to understand local hydroclimatic variability.
Sydney, Australia's largest city, exemplifies the challenges posed by water stress. The city has experienced intermittent droughts and floods in recent decades. During the Millennium Drought (2001–2009), the level of Sydney’s major drinking water supply dam—the Warragamba Dam—fell to less than 33%. The drought ended with the return of a La Niña event in early 2010 that brought high rainfall and large-scale flooding. The recent drought (2017–2019) resulted in a drawdown of Warragamba Dam to 43% capacity by November 2019, which happened after a particularly wet winter and spring in 2016. These events highlight Sydney’s heavy reliance on rainfall and emphasise how the combination of water-related disasters and population growth continues to strain the water supply system [3].
Several pieces of research have been conducted to study the rainfall variability in Sydney’s drinking water catchments. Shrestha, Riley [4] investigated the long-term rainfall pattern in the Warragamba catchment area and analysed the seasonal and annual changes in rainfall patterns. The analysis showed an increasing trend of annual rainfall and a decreasing trend of rainfall in winter over time. Carvalho and Woodroffe [5] analysed the rainfall variability in the Shoalhaven River catchment. The study indicated that approximately twice the amount of rainfall occurred in the lower catchment than further upstream, and the months of Jan-Mar are responsible for about 30% of annual rainfall. However, the Tallowa Dam, as the centrepiece of the Shoalhaven Scheme to supplement Sydney's water supply, collects water from the upper and middle Shoalhaven River. The runoff in the lower Shoalhaven River could be developed as an additional water resource for Sydney through the development of a coastal reservoir [6, 7].
Coastal reservoirs represent a promising solution for addressing water supply challenges...