A water demand and supply analysis under changing climatic conditions was performed for the Chapman Water System on the Sunshine Coast, BC to determine how climate change impacts water consumption and water supply.  Historic temperature, precipitation, and discharge data were collected to determine historic trends.  The impacts from Pacific Decadal Oscillations (PDO) and El Nino Southern Oscillations (ENSO) on climate and discharge were also analyzed to determine how PDO/ENSO enhances the impacts of climate change.  Water consumption data from the Chapman water system was collected to identify relationships between temperature and precipitation.  All of the data were analyzed and used to conduct a sensitivity analysis by developing water consumption scenarios under a 1,2, and 3 °C increase in average summer (July and August) temperatures with and without drought conditions.

Key Findings:

• Since 1962, average annual temperatures have significantly increased and total annual precipitation has significantly decreased.
• Historic climate and discharge trends indicate the total water supply is decreasing from an increase in elevation where snowpack starts to hold significant snow water equivalent, more precipitation falling as rain rather than snow, and earlier snowmelt.
• Temperature was significantly correlated to water consumption, where it was estimated that water consumption will increase by 34 liters per capita per day (LCD) for every 1 °C increase in average daily temperatures during July and August.
• Precipitation was significantly correlated to water consumption, where it was estimated that water consumption will increase by 1.75 LCD per decrease in every mm of total precipitation during July and August, which during drought conditions could be up to 57 LCD.
• The impacts of climate change on water supply can be enhanced from climate variability during PDO and ENSO events and were most notable when warm PDO was in phase with El Nino.
• The current capacity of the existing water treatment plant is most sensitive to climate change and impacts could be experienced in the 5 to 10 years
• The current available water supply may also be impacted if climate trends continue; however, these impacts will likely become severe the next 10 to 15 years.