Modelling London’s Urban Green physiological responses and impacts on flood retention sustainability under climate change

Surface water flooding is the most likely cause of flooding in London, still affecting at least 3% of the area and up to 680,000 properties. Urbanization and climate change are expected to increase the impacts of urban flooding in the near future. To mitigate such problem and provide resilient ecosystem services for Europe’s largest capital, Urban Green Infrastructure adaptations have been extensively used in the last two decades in conjunction with traditional grey infrastructure. Sustainability and efficiency of green infrastructure depend on the ability of plants to emulate the natural ecosystem water and carbon cycles in the city. Considering the expected rise in temperature, changes in rainfall patterns and intensification of the urban heat island effect, existing and planned green infrastructure solutions might be vulnerable to plant water stress. Since there will be much less space available to accommodate future changes in cities, it is extremely important to think about the system’s potential performance further ahead the construction. In this study we perform a detailed evaluation of representative London parks and rain gardens to mitigate flood risk under a changing climate. Specifically, we focus on the hydrological performance of urban raingardens (consisting exclusively of low stature plants) and urban parks (as a composite of low stature vegetation and urban forests) in London. The coupled water and carbon dynamics were evaluated using the ecohydrological model Tethys-Chloris (TeC) forced with the last generation climate change projections UKCP18. Based on our simulation we disentangle the composite effects of climate change, to plant physiological responses to elevated CO2 and changes in precipitation patterns and temperature.

Our results indicate that:

(a) Changes in weather severely affect plant efficiency during the 2^nd half of the 21^st century;

(b) Effectiveness of green infrastructure is strongly dependent on possible climate change outcomes;

(c) Within a certain range of plausible climate changes, for the 1^st half of the 21^st century positive effects of changes in climate can mostly counteract negative plant physiological responses to elevated CO2, but those negative effects gradually become dominant;

(d) Efficient and sustainable design of urban green infrastructure to mitigate flooding must consider an optimal adaptive choice of plants to offset the projected negative impacts of elevated CO2 and uncertain climate.