Environmental Integrity

Nature-Based Solutions for Water - Part Four

Nature-Based Solutions for Droughts and Floods

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TITLE: The United Nations World Water Development Report 2018: Nature Based Solutions for Droughts and Floods

CORPORATE AUTHOR: UNESCO World Water Assessment Programme 

COPYRIGHT LICENSE TYPE: CCBY-SA 3.0 IGO. The text was edited for readability.


As the fifth in a series of annual, theme-oriented reports, the 2018 edition of the United Nations World Development Report (WWDR) focuses on opportunities to harness the natural processes that regulate various elements of the water cycle, which have become collectively known as nature-based solutions (NBS) for water.  Maximizing nature’s potential can help to achieve the three main water management objectives – enhancing water availability, improving water quality and reducing water-related risks.

The number of people at risk from floods is projected to rise from 1.2 billion today to around 1.6 billion in 2050 (nearly 20% of the world’s population). The population currently affected by land degradation/desertification and drought is estimated at 1.8 billion people, making this the most significant category of ‘natural disaster’ based on mortality and socio-economic impact relative to gross domestic product (GDP) per capita.

Water-related risks and disasters, such as floods and droughts associated with an increasing temporal variability of water resources due to climate change, result in immense and growing human and economic losses globally. Around 30% of the global population is estimated to reside in areas and regions routinely impacted by either flood or drought events. Ecosystem degradation is the major cause of increasing water-related risks and extremes, and it reduces the ability to fully realize the potential of NBS.

Green infrastructure can perform significant risk reduction functions. Combining green and grey infrastructure approaches can lead to cost savings and greatly improved overall risk reduction.

NBS for flood management can involve water retention by managing infiltration and overland flow, and thereby the hydrological connectivity between system components and the conveyance of water through it. This makes space for water storage through, for example, floodplains. The concept of living with floods, which, among other things, includes a range of structural and non-structural approaches that help to be prepared for a flood, can facilitate the application of relevant NBS to reduce flood losses and, most importantly, flood risk.

Droughts are not limited to dry areas, as is sometimes portrayed, but can also pose a disaster risk in regions that are normally not water-scarce. The mix of potential NBS for drought mitigation is essentially the same as those for water availability (see Part Two of this series). This mix of NBS solutions improves water storage capacity in landscapes, including soils and groundwater, to cushion against periods of extreme scarcity. Seasonal variability in rainfall creates opportunities for water storage in landscapes to provide water for both ecosystems and people over drier periods. The potential of natural water storage (particularly subsurface, in aquifers) for disaster risk reduction is far from being realized. Storage planning at river basin and regional scales should consider a portfolio of surface and subsurface storage options (and their combinations) to arrive at the best environmental and economic outcomes in the face of increasing water resources variability.