Reducing Climate-Driven Flood Risk Can Be Done In Ways To Also Help Nature Recover

The 2022 Living Planet Report, released earlier this month from the World Wildlife Fund, showed a dramatic decline in monitored populations of wildlife across the world – a 69% decline in abundance, on average, since 1970. A few days ago, I wrote about how halting, and then reversing, this decline will require far more comprehensive actions than what we typically consider as wildlife conservation. In fact, it will require a ‘whole-of-society’ approach.

While that sounds daunting, much of what needs to be done to restore wildlife and nature are transformations that we need to make anyhow for economic security and for people’s health and safety, such as the rapid transition to decarbonized power systems to maintain a stable climate.

Here I will explore one of these needed transformations to make people safer that can be done in ways that also protect or restore wildlife and nature: flood-risk management in response to rising danger from floods, fueled by climate change and other factors. At the upcoming United Nations Climate Change Conference (COP27) next month, governments should make good on past commitments to provide funding for low-income countries to adapt to rising climate risks, including floods, and they can do this in ways that are consistent with protecting and restoring freshwater ecosystems.

River flooding is already the world’s most damaging form of disaster, averaging approximately $115 billion in costs per year. The World Bank reports that 1.5 billion people worldwide are at risk from flooding, with one-third of them considered to be poor and thus particularly vulnerable to property losses, dislocation and economic disruptions.

There are several drivers of rising flood risk globally. First, new development often occurs in areas prone to flooding. A recent study projected that, between 2015 and 2030, nearly half of global urban development—500,000 km², an area the size of Spain—will occur in areas at risk of flooding.

Second, countries with mature systems of flood-management infrastructure (e.g., dams and levees), often have underfunded maintenance and replacement. As a result, these systems are aging and deteriorating. For example, every two years, the American Society of Civil Engineers releases a report card for infrastructure in the United States and their 2021 report card gave both levees and dams a letter grade of “D. ” They noted that hundreds of billions of dollars will be needed to rehabilitate structures to get them up to current standards.

Third, changes in land use are also increasing flood risk. The expansion of urban areas—with their extensive hard surfaces such as buildings, roads and parking lots—prevents rainwater from soaking into the soil, dramatically increasing rates of runoff and flood levels. Drainage systems in agricultural areas can also accelerate runoff and increase flood heights downstream.

Thus, for a variety of reasons, flood risk is rising in much of the world even if temperatures and rainfall patterns were holding steady. But they are not holding steady. The climate change we’ve experienced to date (an approximately 1.2° C increase in average global temperature) is already driving increases in flood frequency and magnitude. Scientists can now do “attribution studies” to discern the influence of climate change on the probability that a given flood event occurred. For example, the research organization World Weather Attribution studied the devastating floods in Europe in the summer of 2021, which killed over 200 people. They concluded that the warming experienced to date had increased the likelihood of a flood event of that magnitude, within a range of 20% more likely to nine times more likely.

Even if we successfully hit the most ambitious climate target (keeping warming below 1.5° C), flood losses will increase considerably. With that level of warming, the number of people exposed to river flooding is projected to increase by 50–60% and flood damages are projected to increase by 160–240% (with global losses reaching nearly US$400 billion per year). Warming of 2° C would result in a doubling of the people affected by floods and an increase in damages up to 520% compared to today. This is a surprisingly large increase in losses relative to warming of 1.5° C, underscoring that seemingly small differences in temperature can have major differences in disruption to people’s lives.

Due to this layering of rising risk on top of current vulnerabilities, keeping communities safe from flooding will need to be a major priority of governments over the next few decades. In the past, flood-risk management has most commonly focused on building dams, levees and floodwalls, designed to keep floodwaters away from people. In addition to the maintenance challenges discussed above, this strict reliance on infrastructure can have a range of unintended consequences. By preventing floodwater from spreading out on floodplains, levees can accelerate flood waves downstream, increasing risk for others. Levees and dams also can produce a misguided sense of security, leading to dramatic increases in development on what are perceived as now-protected floodplains, resulting in far higher damages if a levee fails or is overtopped. As a testament to this effect, annual flood damages in the U.S. tripled in constant dollars during the last century, even as tens of billions was spent on flood-management infrastructure.

Further, dams and levees fragment river systems and disconnect rivers from biologically productive floodplains and wetlands. The Living Planet Index revealed an 83% decline on average in freshwater-dependent vertebrate populations since 1970. Various studies have found that dams and levees are among the leading drivers of the decline of freshwater ecosystems and species.

These various limitations and unintended consequences of engineered infrastructure have led to growing calls from flood managers for a “diversified portfolio” approach.

While keeping floodwaters away from people (e.g., using levees or floodwalls) will remain necessary in many places, that strategy should be complemented by keeping people away from floodwaters, such as through more careful zoning. Flood risk also can be reduced by directing floodwaters to the places we want to flood—wetlands and floodplains—in order to take pressure off the places we don’t want to flood, such as cities and farmlands.

This diversified portfolio approach can make a critical contribution to halting, and even reversing, the decline of nature and wildlife. More careful zoning that avoids development on floodplains will not only keep people out of harm’s way, it will also reduce conversion of these key habitats. Nature-based Solutions (NbS), defined as interventions that use ecosystems or natural processes to achieve a societal goal, can combine flood management with large-scale protection or restoration of floodplains and wetlands.

Specific examples of NbS for flood management include (and see figure below):

· Protection of forests, wetlands and floodplains to store and convey floodwaters to reduce flood levels in other places we want to protect

· Reconnecting rivers with floodplains to allow floodwaters more room to spread out, by repositioning levees further away from the river and/or through features called flood bypasses.

· Using “green infrastructure” in urban areas to slow, hold back and store runoff and allow it to soak into the soil, reducing stormwater and flood risk. These features can include green roofs (vegetation on top of buildings), swales, wetlands and parks. As a bonus, these features can also make cities cooler in the summer and increase access to nature for city dwellers.

· Allowing rivers to deliver sediment to their deltas, building new land and protecting deltas and the people and agriculture that depend on them.

All of these NbS interventions can help halt the decline of freshwater wildlife. If implemented at large scales, they can contribute to the restoration of the habitats they need to recover. At COP26 in Glasgow, wealthy countries have committed to directing $40 billion a year toward climate adaptation in vulnerable countries. At COP27, countries should commit to following through on these pledges. When they do, NbS should play a major role in these adaptation projects, so that the projects needed to keep people safe can also help wildlife recover.

In subsequent posts, I’ll go deeper on these various NbS, including how they contribute to flood-risk reduction and how they contribute to the recovery of wildlife.