Can Nature-Based Solutions Reduce Pluvial Flood Risk? A Case Study on an Institutional Complex.

Abstract

Flood control systems are experiencing increasing pressure and growing threats from the impacts of climate change and urbanization. Nature-based solutions (NbS) provide flood-risk mitigation and ancillary benefits, but their quantitative effectiveness remains inadequately evaluated. This paper aims to provide quantified benefits of risk reduction benefits of having NbS implementation through micro-scale analysis. An institutional compound at Kota Bharu, Kelantan was chosen for the sensitivity analysis, with consideration of green roofs and permeable pavements as the NbS adaptation. Hydrology and hydraulic simulations of flood events show that the implementation of NbS yields a notable reduction of peak flow at high-frequency events, as high as 44.2% from a 5-year return period and 24-hour rainfall duration. Meanwhile, a lower percentage was found for low-probability of occurrence events, with only 0.4% from a 100-year return period. For flood depth, damage, and risk across the range of flood events, the quantified effects of NbS diminish with only less than a 1% reduction of expected annual damage between base and NbS scenarios. The findings suggest that despite the acceptable reduction of runoff, flood damage and risk are not significantly reduced. Thus, integrating NbS with grey infrastructure is essential for effective flood-risk reduction. Keywords: Nature-based solutions, Urban Flooding, Flood Mitigation, Grey infrastructure.