Quantifying Nature-based Solutions for The Hague

Abstract

With a global trend towards urbanisation, the resilience of humanity against economic, social and environmental challenges increasingly shifts from rural to urban areas. Where green and blue infrastructure are expected to mitigate some of the impacts of heat waves or storm events for the urban environment, current assessment methodologies to prove so are lacking. To illustrate the viability of urban Nature-based solutions as alternatives to existing grey infrastructure, this research first looked into assessing the benefits of 4 urban ecosystem services (ES), namely Urban Cooling, Stormwater Runoff Catchment, Carbon Storage and Coastal Protection services. With The Hague as the area of interest, the research was successful in demonstrating positive impacts towards climate resilience for each of the 4 studied ES. First, the presence of urban natural infrastructure was shown to reduce the urban heat island effect by up to 1.5 °C. Green urban areas were further revealed to catch over 50 % of stormwater runoff for major storm events as well as being responsible for the majority of urban carbon storage. Lastly, coastal forests and dunes were proven to be a contributing reason in keeping the overall coastal exposure risk towards inundation and erosion at low to moderate levels. While the initial results of the ES analysis speak for themselves, further evaluation of the employed methodologies revealed major concerns in terms of output consistency and transparency between different tools, such as InVEST and Natural Capital. As the outputs of seemingly analogous models varied greatly and a certain obscurity towards methodological background processes persisted, the results of urban specific assessment models of current ES mapping and evaluating tools require further validation in order to be universally acceptable. The conclusion of this study can help advance the inclusion of urban nature-based solutions into urban policy and planning exercises, while simultaneously raising awareness towards the need for further development of common urban specific ES assessment methodologies.