Changes to the Water Balance Over a Century of Urban Development in Two Neighborhoods: Vancouver, Canada

Hydrological cycles of two suburban neighborhoods in Vancouver, BC, during initial urban development and subsequent urban densification (1920-2010) are examined using the Surface Urban Energy and Water Balance Scheme. The two neighborhoods have different surface characteristics (as determined from aerial photographs) which impact the hydrological processes. Unlike previous studies of the effect of urbanization on the local hydrology, densification of already built lots is explored with a focus on the neighborhood scale. Human behavioral changes to irrigation are accounted for in the simulations. Irrigation is the dominant factor, accounting for up to 56% of the water input on an annual basis in the study areas. This may surpass garden needs and go to runoff. Irrigating once a week would provide sufficient water for the garden. Without irrigation, evaporation would have decreased over the 91years at a rate of up to 1.4mm/year and runoff increased at 4.0mm/year with the increase in impervious cover. Similarly without irrigation, the ratio of sensible heat flux to the available energy would have increased over the 91years at a rate of up to 0.003 per year. Urbanization and densification cause an increase in runoff and increase risk of surface flooding. Small daily runoff events with short return periods have increased over the century, whereas the occurrence of heavy daily runoff events (return period>52 days) are not affected. The results can help us to understand the dominant factors in the suburban hydrological cycle and can inform urban planning.