Climate change adaptation using low impact development solutions in an urban catchment

Climate change refers to the average long-term changes over the whole Earth. Regarding the northern Europe, future climate projections show a general increase of temperature over all seasons. In cold conditions, this change will strongly affect the hydrological features over a year, such as precipitation, snow depth and runoff. Stormwater management is already essential to treat water in urban catchments. Because climate change is complicating urbanization impacts on hydrological features, current stormwater management systems will need to be adapted to altered conditions. Low Impact Development (LID) controls are seen as one option to adapt urban catchments to a changing hydrology. In order to evaluate local climate change impacts on the hydrology and then realize a climate change adaptation, an urban catchment in Espoo, in southern Finland, was studied. The analysis was performed in three time windows: historical, mid- and far-future, according to the RCP8.5 emission scenario. Air temperature and precipitation time-series from HARMONIE-AROME regional climate model were used as input to simulate the hydrological processes in the study catchment using the Storm Water Management Model (SWMM). This study focuses on analyzing changes in urban runoff and snow dynamics. Their behavior was analyzed seasonally and within the water year together with air temperature and precipitation. When the projected mean air temperature increased, snow water equivalent reduced, leaving almost no snow in the far-future period. This in turn altered the seasonal runoff behavior both in mid- and far-future periods. In fact, mid-winter runoff was modelled to increase considerably, while spring runoff was expected to decrease with respect to historical period. The highest runoff volume and peak flows will still occur in summer. Thus, in order to alleviate for the climate change impacts on urban hydrology, the stormwater management can be used for adaption by installing LID solutions to reduce the total runoff volume in summer. The subcatchments of Vallikallio with the highest total runoff volumes were identified to select locations for LID implementation with high impacts on runoff. The performance of bio-retention cells, permeable pavements and green roofs was evaluated to investigate if and to what extent LID solutions can aid in the mitigation against climate change impacts on the urban runoff regime. All the selected LID scenarios achieved the total runoff volume reduction in summer, having an impact during the other seasons. While permeable pavements and bio-retention cells were projected to behave similarly within the water year, green roofs had a negligible runoff volume reduction in winter. Bio-retention cell scenario was the one that required the lowest LID coverage compared to the other scenarios, with the same scope.