To assist the City of Surrey with its understanding of local historical climate trends, Dillon completed a climate trend analysis using hourly rainfall data over a 47 year period.
The analysis included a detailed examination of the full suite of rainfall events (2, 6, 12, 18 and 24 hr, 2 day, 5 day, monthly and annual events) identified in the historical record at a number of sites. Select key duration events were found to change at significant levels:
- overall monthly rainfall has increased with the exception of the month of February, where a decreasing trend was identified
- monthly rainfall in January at all three stations exhibited statistically significant increases
- 2 hour and 6 hour rainfall events in the north (Kwantlen Park), 12 hour and 18 hour rainfall events in the south (White Rock) increase at significant levels
- annual rainfall at all stations has slowly increased in the past 47 years.
If the identified trends continue, rainfall indicators could increase by up to 30% in 2025 and 60% by 2040.
A closer examination of the trends showed there to be variability across the city. This analysis made the following conclusions:
- Rainfall statistics within the city have changed significantly, including the number of more extreme hourly rainfall events showing the highest increases in the last two decades
- El Nino and La Nina events could intensify, resulting in more extreme weather events
- The implications of climate change on the city’s infrastructure should be explored, specifically looking at updating design standards to account for this change.
The study allows the City to better assess the performance of critical infrastructure, identify areas of flood susceptibility and plan future infrastructure initiatives while aiding the City in determining the best way to spending infrastructure budget to ensure the best return on investment for the city.