1. Scope

This guide provides a set of options, with technical guidance, for the use of Nature-based solutions in the mitigation of increased precipitation driven flood impacts to inland waterways under changing environmental conditions. It includes adapting improved management strategies for watersheds, wetlands, streams, reservoirs and rivers. The guide reflects changes in climatic conditions, urban and rural land use, and extreme weather events that impact stormwater runoff and retention. Nature-based solutions are sustainable planning, design, environmental management and engineering practices that weave natural features or processes into the built environment and promote adaptation and resilience.1 The approach presented in this guide may help either initiate, or further promote existing assessment and risk management programs, such as the restoration of natural habitats as part of the decision-making process. This guide provides a voluntary framework of the risk management options and steps that may be beneficial to evaluate climate resiliency solutions. It provides strategies for any organization, even those currently operating outside of various voluntary and regulatory schemes. The environmental assessment and risk management strategies contained in this guide recognize the overall value of existing approaches. This guide references and merges similar, effective programs and tailors them for a consistent approach that will facilitate communication and preparation. A key concept is the protection of the human-built environment and national water resources under changing environmental conditions.
1 FEMA https://www.fema.gov/emergency-managers/risk-management/nature-based-solutions

Keywords

Nature-based Solutions; flood; inland flooding; watershed; climate change; green infrastructure

Rationale

The number of floods in the US (excluding tropical cyclones) exceeding 1 billion dollars in damages has increased from 4-8 per decade (1980-2009) to 18 in a single decade (2010-2019).2 Almost 23% of the world’s population (1.81 billion people) are now exposed to flood depths greater than 0.15 meters in a 100-year flood event (floods from all causes), driven by complex interactions between climate change, urbanization, and socioeconomic factors. The Upper Mississippi River basin, like many river watersheds, is experiencing an increase in both the amount and the intensity of precipitation events, leading to the river being above flood stage at several locations for 5-10 times as long in the past decade compared to the previous 80 years. 4 The recent increase in flood frequency, magnitude, duration and economic impact has resulted in a need for additional cost-effective, large-scale approaches that use natural systems to help mitigate inland flood impacts.

This guide covers options for using Nature-based solutions to help mitigate impacts from rainfall driven inland flooding along streams, rivers, reservoirs, lakes and wetlands. It does not cover flooding caused by infrastructure failure, coastal flooding impacted by sea-level rise, flooding caused by cyclones, or flooding from snowmelt or glacial melting. This guide presents options for Nature-based Solutions focused on watershed level management options, to complement current flood mitigation strategies used at the national, state, municipal and local level.

2 NOAA National Centers for Environmental Information (NCEI) U.S. Billion-Dollar Weather and Climate Disasters (2023). https://www.ncei.noaa.gov/access/billions/, DOI: 10.25921/stkw-7w73
3 https://www.nature.com/articles/s41467-022-30727-4
4https://www.noaa.gov/sites/default/files/2022-03/Technical_Version_Upper_MS_River_Communicating_CC.pdf

The title and scope are in draft form and are under development within this ASTM Committee.