Stochastic Generation of Future Hydroclimate Using Temperature as a Climate Change Covariate

• Published in: Water resources research 2021-02, Vol.57 (2), p.n/a
• Main Authors: Kiem, Anthony S., Kuczera, George, Kozarovski, Pavel, Zhang, Lanying, Willgoose, Garry
• Format: Article
• Language: English
• Subjects: Annual; Annual rainfall; Catchment area; Catchments; Climate change; Climate models; climate variability; drought; Evapotranspiration; Future climates; Hydroclimate; Maximum temperatures; Potential evapotranspiration; Rain; Rainfall; Security; Statistical analysis; Statistical methods; stochastic; Stochastic models; Stream discharge; Stream flow; Temperature; Temperature changes; Water security; Water shortages; Water supply
• ISSN: 0043-1397; 1944-7973
• DOI: 10.1029/2020WR027331

It is now standard practice for water supply agencies to use stochastic models to generate synthetic hydroclimate sequences that preserve the key statistics contained in the observed/instrumental hydroclimate data (usually rainfall, potential evapotranspiration, and streamflow) for use as inputs when determining water security. However, this approach is only adequate for determining current and future water supply risks if nonstationarity in past and future climate is accounted for. In this study, we develop an approach for stochastically generating future seasonal (monthly to annual) hydroclimatic conditions at multiple sites for water supply security assessment that capitalizes on an Australia‐wide relationship between annual average daily maximum temperature and annual rain (and flow). This approach is practical as it (i) avoids the extra time and additional uncertainties introduced by downscaling and bias correction of climate model produced rainfall information and (ii) takes advantage of the fact that climate model projections for temperature change are more realistic than climate model projections for rainfall. The approach is applied to a case study for catchments supplying Sydney, Australia's largest city. Two future scenarios were evaluated, 1 and 2°C warming over the next 50 years. Large reductions in streamflow were simulated, particularly for the 2°C scenario, resulting in major impacts on water security in the absence of any intervention. This is consistent with recent warming since 1990 being associated with more than a 40% decrease in average annual streamflow when compared with the average annual streamflow over the ∼110 years historical record. Key Points Generate future hydroclimatic conditions for water security assessment using the relationship between temperature and rain (and stream flow) Recent warming (2000–2018) in Sydney, Australia associated with a 43% decrease in average annual streamflow when compared with the post‐1910 average Future warming is associated with even larger reductions in average annual streamflow resulting in major impacts on water security in the absence of any intervention