In planning for the provision of future water supplies, water planning engineers have traditionally considered mean historical rainfall, runoff, evaporation, water storage capacity and water use data. For urban centres, assessments of water availability and annual water demand have been simply carried out with limited consideration of the trends now being reflected in the form of increasing drought persistance.
Both historical and stochastic modelling techniques have been used in Australia to simulate the performance of urban water supply storages. Historical modelling has been used to demonstrate how the water supply would have performed under historical climatic conditions for a range of demand levels and operating arrangements. Stochastic modelling has been used to demonstrate how the water supply storage would have performed under a wider variation of potential climatic scenarios, including more severe droughts. The severity of drought is measured by its duration and magnitude of rainfall deficit.By considering the frequency and severity of droughts, including trends in increasing duration and magnitude, which are not included in stochastic modelling, a clearer understanding of future water supply storage and operation requirements can be determined.
Water supply planning requires not only an understanding of likely and potential changes in water demand but also an understanding of how climate is changing. This paper investigates trends in drought persistence variability and associated meterological drivers, and how with adequate understanding water supply can be managed to ensure minimal consequences, adequate time and ability to respond with alternative supply options, acceptable reliability (frequency of restrictions) and costs (cost of supply versus cost of failure) and meet user expectations.
Traditional storage yield estimation is now broadly being questioned as new norms are being established necessitating and increased understanding of how climate is changing. Some of the key climate drivers for the world appear first and most strongly between Australia and Mexico in the Pacific Ocean. These include the El Nino Southern Oscillation and other key Pacific drivers that are potentially being influenced by neighbouring climate drivers. This paper describes how changes in the strengths of climate drivers resulting from warming in the northern hemisphere may potentially impact equatorial winds and consequently water scarcity, which has implications for associated water supply planning, through affecting the duration of El Nino and La Nina outputs for Australia and Mexico.