Globally, floods have had the highest occurrence (43%) and damages ($40 billion) of all natural disasters; from 1994 to 2013 almost 2.5 billion people were affected. The problem is being exacerbated by climate change, urbanization, agriculture expansion, deforestation, and poor land development. In addition, extreme weather events and associated are expected to increase in the future.
Traditionally, flood mitigation has used grey infrastructure measures such as concrete channels for rivers, pipes, dams and levees, and impermeable surfaces like roads and parking lots. The main goal of grey infrastructure is to collect and remove stormwater as quickly as possible. Alternatives to traditional measures are nature-based solutions (NBS)
NBS are showing great potential in reducing the peak flood flows, as they are able to keep stormwater on site where it can be reduced, stored and slowly released, and made available for ecosystem services. Both small-scale NBS (e.g., green roofs, bioswales, rain gardens, infiltration trenches) and large-scale NBS (e.g., wetlands, floodplains, ponds) help reduce the intensity of flooding.
Four cities in Laos on the Mekong River are shifting the focus away from grey infrastructure to NBS to control flooding and become more resilient to climate change. A new program of NBS aims to protect and restore over 1500 hectares of wetlands and urban forests, and thereby provide benefits such as improved infiltration, water storage, flood mitigation, improved biodiversity, habitat, and water quality.