Surface Water Quantity for Drinking Water during Low Flows - Sensitivity Assessment Solely from Climate Data

The future sensitivity of the surface water supply of Québec City is assessed in this paper using two methodologies: the methodology that has prevailed since the publication of the AR4 report, the hydroclimatological modeling framework, and an alternative approach adapted from Foulon et al. (2018). This alternative approach captures past relationships between climate data indices (CDIs), such as cumulative rainfall, and hydrological data indices (HDIs), such as 7-day low flows, and applies these relationships to assess future trends. Future climates were built for two emission scenarios, RCP-4.5 and − 8.5, and the uncertainty of climate change was addressed through the use of 16 climate models. Overall, both methodological frameworks predicted similar low flow trends for the reference and future horizons (2016–2045 and 2046–2075). The future pressure on the surface water supply of Québec City should raise concerns. Indeed, for RCP-8.5, results indicated a decrease in the PI1 values (ratio of 2-year low flow to water abstraction rate) of around 20% (2016–2045) and 35% (2046–2075) with a fairly high confidence (around 90% of models agreeing on the direction of change); leading to values less than 1; indicating an insufficient water supply with respect to available water during 2-year low flows. These results demonstrate the capacity of the method to provide a screening assessment of future drought-prone-watersheds. Furthermore, the application of the alternative approach, given climate simulations, would help early implementation of good management practices even for municipalities that do not have the capacities to conduct the more conventional approach.