Time series monitoring of impervious surfaces and runoff impacts in Metro Vancouver

Abstract

Urban areas are increasing rapidly worldwide, leading to widespread changes in land surfaces over time. Urbanized land cover is heterogeneous, and is characterized by a large areal proportion of manufactured impervious surfaces which are linked to ecological degradation, habitat loss, and increase in precipitation runoff leading to pollution and safety risks. Data from the Landsat series of satellites present an opportunity to characterize urban land cover and impervious surfaces, over a large spatial and temporal scale. In this study, land cover changes from 1990 to 2015 are characterized in the large metropolitan area of Metro Vancouver, Western Canada. An ordinal regression is used to link Landsat spectral data with a detailed land classification containing classes of impervious surface used by municipal planners in the region (Spearman's Rho = 0.76). The regression is then used to classify a time series of imagery where static land classifications are not available, providing a 25-year time-series of change in impervious surface area. A trend in increasing impervious surface was detected across the municipalities in the region, with an overall areal increase of 31.96%. Precipitation events were then simulated at each time step, using precipitation rates adjusted for expected changes in climate by 2050. Both runoff depths and inundated area increased over time, with a 51% increase in area inundated by at least 5 cm. Runoff depths were evaluated for each municipality in the region, and compared to projected populations for 2050 to highlight communities that may face elevated levels of runoff risk. Results show a steady increase in impervious surfaces in the region. Impacts of future extreme precipitation events vary across the region, with flat and low-lying topographies appearing to be more severely affected, along with areas containing extensive impervious development.