Flood Risk Management Driven by Naturebased Solutions: From Watershed Ecosystem Services to Resilience Enhancement under Climate Change

Abstract

Climate warming is increasing levels of flood risk worldwide because it increases heavy precipitation, runoff and floodplain encroaching accelerates land use change, and concentrates people and assets in flood prone areas. Due to the creation of nonstationary hazard regimes due to the process of climate change, flood governance can no longer be based only on the statistics of events in the past or predetermined design criteria. Traditional grey-only techniques of flood control, such as levees, channelization and hard shorelines structures can provide temporary risk alleviation, but frequently take a toll on river structure, decouple floodplains, shift risk along stream or through time and can lock societies into unbending infrastructural courses that can destroy ecosystems and reduce adaptive capacity.

As proposed by the IUCN and gaining growing root in the UN policy processes, as well as regional level policy, Nature-based Solutions (NbS) demonstrate another avenue of flood risk management, which consists in protecting, restoring or sustainably managing ecosystems to sustain societal needs and deliver ecosystem services, biodiversity benefits and co-benefits to human well-being. In a synthesis of NbS-based flood risk management synthesized in a watershed-to-resilience perspective, this paper integrates (i) hydrological and ecological processes operating, respectively, along the catchment continuum (headwaters to river corridors to floodplains to deltas/coasts to urban systems), (ii) watershed risk-reduction pathways, which operate on hazard, exposure, and vulnerability, and (iii) assessment approaches, which convert ecosystem service delivery into decision-relevant measures, such as ecosystem accounting frameworks (e.g On the whole, the evidence suggests that NbS can offset flooding and improve resilience, yet the influence depends on conditions and may be insignificant in extreme cases; thus, hybrid green-grey portfolios, stress testing at scenarios under non-stationary conditions, and strict monitoring are needed to match the implementation with the Sendai Framework on Disaster Risk Reduction and the IUCN Global Standard on NbS.