Can your urban area sustainably adapt to climate change? Insights from Southern Finland

The study, recently published in the Boreal Environment Research journal, centered on the suburban area of Vallikallio in Espoo, Finland. It projected future climate scenarios to assess changes in hydrological processes, comparing historical and future data. The study then applied a methodology to design low impact development (LID) solutions, including green roofs, permeable pavements, and bioretention cells. LID solutions reduce the impermeable surfaces in the city, thereby reducing runoff and decreasing the risk of floods.

Under the pessimistic emission scenario RCP8.5, the study predicts a significant reduction in snowfall, with near-future projections showing a decrease of over 50%, and nearly complete disappearance of snow by the end of the century. Rising temperatures will lead to more rain and earlier snowmelt, resulting in increased runoff throughout most of the year, except for spring.

All LID solutions effectively reduced future summer runoff levels to match historical levels, with bioretention cells requiring the smallest area coverage, while green roofs necessitated the largest. However, the most substantial variation in LID performance was observed during the winter season. Green roofs, relying on evapotranspiration, could not provide significant runoff reduction due to winter weather limitations. Permeable pavements and bioretention cells performed similarly in reducing runoff, though not entirely. In spring, a natural runoff reduction was projected even without LID implementation, so LIDs are projected to further reduce runoff in this season.

Importance of addressing seasonal performance of LIDs

The study proposes a transparent method to adapt the current urban stormwater management systems by using LID solutions. In fact, besides the study case regards an urban catchment of the southern Finland, the methodology can be applied to every catchment, because it guides on choosing the amount (m²) of LIDs needed to manage the future runoff, and the optimal locations to place the LIDs.

In addition, the study found that LID solutions designed for reducing runoff in one season may not work the same way in other seasons, especially in places with big seasonal changes like boreal regions. For example, in the specific study case, the LID solutions were designed to reduce summer runoff to historical levels, but this didn't work well for reducing winter runoff, and even further reduced spring runoff. So, these findings are important for addressing the performance of stormwater management solutions throughout all seasons in urban areas within boreal environment.

Further information:

Doctoral researcher Carla Maria Di Natale, Finnish Meteorological Institute, carla.di.natale@fmi.fi

Scientific article is available on Boreal Environment Research journal.

Reference: Di Natale C. M., Tamm O. & Koivusalo H. 2023: Climate change adaptation using low impact development for stormwater management in a Nordic catchment. Boreal Env. Res. 28: 243–258.

The research was conducted as part of the EviBAN project and led by Carla M. Di Natale, Ottar Tamm, and Harri Koivusalo. The analysis utilized air temperature and precipitation data from the regional climate model HCLIM, incorporating the RCP8.5 emission scenario as input into the Storm Water Management Model (SWMM). The study was conducted in 2022.

This work was supported by the EviBAN project funded by the EU Water JPI and the Academy of Finland (no 326787).