A decade ago Hurricane Katrina devastated the gulf coast; and New Orleans’ levees failed, flooding about 80% of the city. Three years have passed since Superstorm Sandy became the second costliest hurricane in U.S. history. Climate change is bringing new realities to the world: sea level rise and the increased severity of storms, flooding, and drought. Together, climate change and urbanization are causing costlier and deadlier natural disasters.

Action on climate change culminated in a historic agreement between 195 nations on Dec. 12, 2015 in Paris. The main goal of the low-carbon agreement is to keep global temperature rise below 2°C within this century. However, nations will strive to limit the temperature increase even further to 1.5°C above pre-industrial levels. This is a significantly safer defense line against the worst effects of a changing climate.

Despite efforts to mitigate climate change, cities also must adapt. In 2015, communities across the U.S. and internationally made strides toward preparing for climate change. A number of these resiliency efforts took the form of sustainable stormwater management, as communities embrace green infrastructure to prepare for flooding and drought.

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Observed Change in Very Heavy Precipitation Caption: The map shows percent increases in the amount of precipitation falling in very heavy events from 1958 to 2012 for each region of the continental United States. Adapted from Global Climate Change Impacts in the United States.

The map shows percent increases in the amount of precipitation falling in very heavy events from 1958 to 2012 for each region of the continental United States. Adapted from Global Climate Change Impacts in the United States.

A review issued by the United Nations shows that between 1995 and 2015, floods accounted for 47% of weather-related disasters. Mitigating flooding is a primary goal of efforts to control urban runoff and makes sustainable stormwater management an integral component of resiliency.

Though the stormwater sector has long focused on flooding and is now shifting its focus toward water quality, climate change is causing cities to revisit their grey infrastructure capacity and to embrace new green infrastructure solutions.

According to the U.S. Global Change Research Program’s National Climate Assessment, the amount of rain failing in very heavy precipitation events has been significantly above average since 1991. Heavy rainfall has increased more than 30% compared to the 1901–1960 average in the U.S. Northeast, Midwest, and upper Great Plains.

Urban centers especially are vulnerable, yet development and population growth continues along coasts and in flood-prone areas. A March 2015 study by Texas A&M researchers, shows that urban land cover located in high-frequency flood zones is expected to increase by 1.2 million km2, from 30% in 2000 to nearly 40% by 2030.

This combination of climate change and urbanization — especially along coasts and flood-prone areas — is causing costlier and deadlier floods. During the past 20 years, the UN conservatively estimates that floods affected 2.3 billion people and killed 157,000. An analysis by the World Resources Institute and four Dutch research organizations, concludes that 21 million people currently are affected by river flooding each year on average around the world. This number could increase to 54 million by 2030 due to climate change and development.

As flooding increases and more people are affected, costs invariably rise as well. The Insurance Bureau of Canada states that internationally insured losses from natural catastrophes ranged between $10 billion and $50 billion per year over the past decade. The World Resources Institute study shows that floods currently disrupt $96 billion in gross domestic product, a number the researchers say could increase more than five times to $521 billion by 2030.

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Achieving a sustainable stormwater sector that contributes to community resiliency is a primary goal of the Water Environment Federation (WEF) Stormwater Institute. The institute officially launched at WEFTEC 2015 in Chicago with the release of Rainfall to results: The future of stormwater. The report details the challenges, opportunities, and pathways that will lead to more effective stormwater management. The report draws from the insights of top stormwater experts from across the U.S. and will help shape the future actions of the institute.

The institute is housed within WEF to leverage the organization’s existing leadership, breadth of membership, and varied partnerships with federal, state, and local entities responsible for managing stormwater issues. The growing issue of stormwater pollution coupled with regulatory pressure has created a need for national leadership that the WEF Stormwater Institute aims to provide. The institute will have a strong initial focus on the development of technical tools, professional training, and networking opportunities for stormwater practitioners worldwide. Many existing stormwater initiatives within WEF will be brought under the umbrella of the institute, and new programs focusing on key sector needs will be developed.

Integral to the vision outlined in Rainfall to results is that all stormwater is considered a resource and managed through an optimized mix of affordable and sustainable green, gray, and natural infrastructure. Communities across the globe are beginning to recognize the value of stormwater. These communities are embracing green and natural infrastructure to reduce flooding, combat drought, and augment groundwater supplies.

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As leaders from around the world gathered in Paris for the United Nations Conference on Climate Change, the 100 Resilient Cities initiative ― which is pioneered by The Rockefeller Foundation ― announced the 10% Resilience Pledge. According to 100 Resilient Cities, $5.2 billion dollars committed by an initial 22 cities represents the most ambitious financial commitment to urban resilience yet. Mayors of the signatory cities pledge 10% of annual city budgets toward defined, resilience-building activities throughout their term in office. Such activities include investments in green and grey infrastructure that protect water quality and prevent flooding.

New Orleans was among the signatories of the pledge. In August, the city also became the second member of the 100 Resilient Cities initiative ― following New York City ― to release its resilience strategy. Unveiled in August 2015, Resilient New Orleans calls for a comprehensive stormwater management program.

In the 10 years since Hurricane Katrina, New Orleans has spent billions of dollars to improve the city’s flood defenses. The Hurricane and Storm Damage Risk Reduction System is a massive system of levees, floodwalls, pump stations, and outfall canals capable of protecting the New Orleans metropolitan area against 100-year storm surge events.

Not only has the city shored up its grey infrastructure, but a new focus on green infrastructure is helping the city address flooding associated with common storm events as well as subsidence and urban blight. A key strategic action of Resilient New Orleans is implementing the Greater New Orleans Urban Water Plan. Influenced by Dutch experts with extensive experience managing water in low-lying areas, the urban water plan views stormwater as a resource. It focuses on decentralized, landscape-based solutions that infiltrate stormwater. During the next 50 years, the urban water plan is expected to cost $6.2 billion, but is expected to generate $22 billion in economic benefits, including those associated with reducing flooding, subsidence, and flood insurance premiums. Additionally, the plan would generate $11.3 billion in benefits from job creation and $183 million in increased property values.

Guided by the urban water plan, the New Orleans Sewerage & Water Board also now has a green infrastructure plan that is part of a modified consent decree to reduce sewer overflows. The city’s first-ever zoning ordinance to require some residents to collect stormwater on their property also went into effect in the summer of 2015.

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Changes in New Orleans echo a national trend toward using more natural solutions to manage rain where it falls and to protect shorelines from intense storms, erosion, and sea level rise. This infrastructure ranges from such site-scale practices as bioswales and green roofs to such large-scale natural features as coastal wetlands or stream buffers.

Natural infrastructure offers a cost-effective means of improving water quality, reducing sewer overflows, and mitigating flooding while revitalizing communities and making them more resilient to the effects of climate change. For example, a Nature Conservancy case study of Howard Beach, a coastal community devastated by Superstorm Sandy, shows that a combination of natural and engineered infrastructure is the most effective means of increasing resilience. This combined approach could result in avoided losses of up to $244 million from a one-in-100-year storm.

In fall 2015, the Obama Administration released a memorandum directing federal agencies to factor the value of natural infrastructure and ecosystem services into federal planning and decision-making. Beyond the U.S., a number of countries made commitments to use green infrastructure in 2015, including Peru, China, and the United Kingdom.

In early April, China’s central authorities announced 16 cities that will participate in Sponge City pilots. Over the next 3 years, the pilot cities will install low-impact development features to capture and use nearly 70% of rainwater, as reported by China Radio International. These systems are expected to reduce flooding from under-developed drainage systems and provide a water source in drought-prone areas of the country.

In Lima, Peru, the city’s water utility, Servicio de Agua Potable y Alcantarillado de Lima, announced green infrastructure commitments to address drought, flooding, and erosion ― issues that are expected to worsen with climate change. US$23 million will be dedicated to green infrastructure while $89 million will be used for general climate-change adaptation and disaster-risk reduction. In this context, green infrastructure includes natural wetlands and pre-Incan canals. The canals siphon water off high-altitude streams in the wet season and funnel the water into the mountains. The water filters down through the rocks over several months and emerges from springs in the dry season.

In March, the UK’s Department for Environment, Food & Rural Affairs released non-statutory technical standards for the design, maintenance, and operation of sustainable urban drainage systems (SuDS). These standards follow changes to the planning system specifying that SuDs be used whenever appropriate in new development. Additionally, in October, London announced its SuDS action plan. The plan is intended to address major flooding risks posed by population and climate change pressure on the city’s aging drainage and sewerage systems.

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Tree ring data suggests that droughts in the western U.S. over the last decade represent the driest conditions in 800 years. According to the National Climate Assessment, long-term droughts are expected to intensify across large portions of the U.S. Southwest, southern Great Plains, and Southeast.

However, some communities are using the same solutions for deluge and drought. A report released in December 2015 by the National Academies of Sciences, Engineering, and Medicine states that graywater and stormwater could significantly supplement traditional potable water supplies.

In April 2015, following months of severe drought and the lowest snowpack ever recorded in the state, California announced its first-ever statewide mandatory water reductions. In June, an order adopted by the California State Water Resources Control Board created a framework promoting integrated stormwater capture and reuse to improve water quality, protect local beaches, and supplement water supplies. The new permit focuses on using stormwater as a resource and encourages green infrastructure and groundwater recharge.

Currently, the City of Los Angeles and its partners actively capture approximately 36 million m3 (29,000 ac-ft) of stormwater each year, which is used to recharge groundwater. Captured stormwater along with incidental recharge account for 10% of the city’s annual water demand. Guided by its Stormwater Capture Master Plan finalized in August 2015, the city could capture an additional 84 million to 141 billion m3 (68,000 to 114,000 ac-ft) per year, in part through decentralized green infrastructure practices. The city expects to address multiple priorities with green infrastructure, including reducing peak flows in area waterbodies, improving water quality, and mitigating the effects of climate change. In summer 2015, Los Angeles County also announced plans to develop a countywide network of stormwater capture and improvement projects. The ambitious Enhanced Watershed Management Plans are the result of a multi-year collaboration between the state, county, and 49 area cities across 12 watershed groups to improve local and regional water supplies and waterways.


Los Angeles’ plans emphasize the importance of enabling infiltration and increasing groundwater augmentation where safe. Reliance on groundwater increases during drought. Groundwater now accounts for about three-quarters of California’s water; in the past groundwater made up a third of the state’s water supply. Groundwater levels across much of the state have dropped 15 m (50 ft) below historic lows, the California Department of Water Resources reports. In many areas of the San Joaquin Valley, groundwater levels have dropped more than 30 m (100 ft) below previous record lows, causing the land to sink nearly 5 cm (2 in.) per month in some locations.

According to the U.S. Geological Survey (USGS), groundwater provides drinking water for about 115 million people, or more than a third of the U.S. population. At the start of 2015, USGS released its national summary report on the quality of the country’s groundwater. The report showed that over-pumping to meet increasing water demands is changing groundwater flow and quality profoundly in many areas. Additionally, 22% of groundwater samples contained at least one contaminant in concentrations of potential human health concern.

A study by researchers at the universities of Victoria, Texas at Austin, Calgary, and Göttingen published in the journal Nature Geoscience in Nov.2015, estimates the Earth’s total supply of groundwater. The study shows that less than 6% of groundwater in the upper 2 km (1.24 mi) of the Earth’s landmass is renewable within a human lifetime.

Better understanding of groundwater availability, quality, and potential contamination sources is key to sustainable management of this vital resource, especially as population and climate pressures increase. A promising endeavor announced in September 2015 will improve access to scientific and technical groundwater information in an aggregated dashboard. This partnership between Qlik, Circle of Blue, Columbia Water Center, University of California Irvine, and the Pacific Institute ― with data support from Twitter ― is intended to uncover groundwater data insights that drive action toward long-term sustainability.

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Greening MS4s

The U.S. Environmental Protection Agency (EPA) has supported the integration of green infrastructure into stormwater regulatory frameworks since 2007 and now actively promotes green solutions as a way to improve climate resilience. 2015 marked the 25th anniversary of EPA’s stormwater permitting program, which regulates municipal separate storm sewer systems (MS4s).

Stormwater permits in at least 17 states and the District of Columbia currently use retention-based performance standards for new development and redevelopment. Such standards encourage green infrastructure and were a probable aspect of EPA’s proposed stormwater rule. EPA deferred the proposed rule in 2014, and shortly after, the agency announced plans to improve stormwater management and encourage infiltration practices through existing Clean Water Act authorities, such as MS4 permits and total maximum daily loads (TMDL).

Despite deferment of the proposed rule, communities across the U.S. are making progress on developing robust stormwater programs. To recognize such high-performing communities for their efforts, WEF launched the National Municipal Stormwater and Green Infrastructure Awards program in 2015 through a cooperative agreement with EPA. Winners of this inaugural competition with the highest overall score include the Phase I City of Charlotte, North Carolina as well as the Phase II City of Fairbanks, Alaska.

The City of Fairbanks, the northernmost MS4 community in the U.S., is taking an approach to green infrastructure that is adapted uniquely to cold climates. Among its many innovative programs, Charlotte-Mecklenburg Storm Water Services manages a stream and wetland mitigation bank called the Umbrella Bank. Storm Water Services also conducts a floodplain buyout program through which it acquires commercial or residential properties and restores the sites to a natural state.

Growing Green Assets

Across the U.S., more than 770 communities also are dealing with combined sewer overflows (CSO). EPA has addressed CSO issues through federal consent decrees in 47 communities. In a report released in September 2015, EPA’s inspector general calculates that these consent decrees will eliminate at least 286 million m3 (75.5 billon gal) of CSO discharges annually — 8% of the estimated total — and cost more than $32 billion. However, the report states that the agency is not effectively tracking community progress on reducing CSOs. Without such an assessment, it is difficult to determine whether EPA’s CSO enforcement initiative has resulted in improved water quality, the inspector general states.

Yet, many CSO communities are making significant progress. And many are implementing large-scale green infrastructure programs to reduce the amount of runoff reaching combined sewers as well as the amount of ratepayer money flowing into wet weather solutions. Some of these programs have been ongoing for more than 5 years now.

WEF’s Rainfall to results report calls for stormwater systems that are maintained through robust asset management that is supported by innovative information technology. A growing wealth of data is a trend for both MS4 and CSO programs. These data will help prove the value of stormwater systems and provide feedback for enhancing their performance.

For example, an analysis released by New York City in March 2015 shows that green infrastructure can play an important role in improving the health and cleanliness of local waterways. Cost-effective practices performed even better than expected, reducing flow to sewers by more than 20%.

Since 2011, DC Water in Washington, D.C., has explored the use of green infrastructure. In May 2015, the utility announced that it will incorporate $2.6 billion in green infrastructure into its Clean Rivers Project to reduce CSOs. With large-scale investments in green infrastructure planned, DC Water developed a robust asset management program. The asset management framework was shaped by the experiences of other green infrastructure programs across the U.S. and by the utility’s own extensive experience managing water and sewer assets. Using an adaptive framework, DC Water created an approach that ensures green infrastructure performance but also focuses on increasing performance and maintenance efficiency over time.

WEF’s Rainfall to results also calls for a multidisciplinary workforce that will support sustainable stormwater management. DC Water has agreed to support local job creation by committing to hire district residents for 51% of new jobs associated with green infrastructure contracts or procurements. To develop a skilled workforce, the utility announced in 2015 that it is partnering with WEF to create a national green infrastructure certification program for construction, inspection, and maintenance.

Integrated Solutions

In recent years, EPA has begun encouraging the integration of municipal wastewater and stormwater management. Historically, communities have focused on meeting each Clean Water Act requirement separately. However, the integrated planning framework enables communities to prioritize investments that address the most serious water quality issues first. The framework encourages cost-efficient solutions such as green infrastructure that can address multiple priorities.

Yet, there is an ongoing need for guidance. In 2015, the Water Environment Research Foundation announced that it is developing a toolbox to help communities manage compliance with water quality regulations in a way that integrates multiple disciplines. Since EPA launched the framework in 2012, few integrated plans have been approved officially.

Seattle’s integrated plan, once approved by EPA, will enable the city to implement stormwater control projects that significantly benefit water quality, while delaying lower-benefit CSO projects. Approved by the city council in 2015, Seattle Public Utilities’ 15-year integrated Plan to Protect Seattle’s Waterways will prevent untreated wastewater and polluted runoff from flowing into area waterbodies like Puget Sound. Seattle and King County manage interconnected combined systems, and over the last 50 years, they have reduced annual CSO discharge volumes by an estimated 76 million to 114 million m3 (20 billion to 30 billion gal). However, limited resources have been available to address the water quality effects of MS4 discharges.

The integrated plan also ties into Seattle’s recently released Green Stormwater Infrastructure Strategy, which will help the city meet its goal of managing 2.7 million m3 (700 million gal) of runoff annually with green stormwater infrastructure by 2025. The plan will enable Seattle to fulfill obligations under Washington State Department of Ecology’s 2015 stormwater permit, which requires the entire state use low-impact development.

Increasing Data for Better Outcomes

While WEF’s Rainfall to results report calls for more integrated planning to transform stormwater governance, it also recommends regulations focused on program outcomes. As opposed to requiring a specific action or technology within a permit, performance-based criteria focus on how solutions perform or whether programs are meeting water quality objectives. To achieve outcome-focused programs, better tracking and monitoring are necessary, and trends are moving in this direction.

New technologies and partnerships are making it easier to monitor stormwater infrastructure. For example, partnerships among universities and cities are increasing internationally to fill this need. In summer 2015, the National Science Foundation granted $12 million awards to three separate university networks to conduct integrated research on urban resiliency solutions. Research and monitoring data can translate into actionable information about performance, and it can inform future maintenance schedules and capital expenditures.

In 2015, EPA finalized a rule requiring electronic reporting for municipalities, industries, and other facilities under its Clean Water Act programs. This includes changes in reporting for MS4s. According to the EPA, this rule will provide a nationally-consistent set of NPDES program data that is timelier, more accurate, more complete and that provides greater clarity on who is in compliance. Collecting program data electronically will likely enable the agency to do additional analyses revealing national trends.

Stormwater in the Courts

However, in 2015, EPA faced litigation on several fronts affecting stormwater regulations. At the close of 2015, EPA released a proposed remand rule for its Phase II MS4 permit. The proposed rule addresses how small MS4s seek and incorporate public comment and agency reviews into their permits. The proposed rule is the result of a settlement between EPA, the Natural Resources Defense Council, and the Environmental Defense Center Inc. The agency is obligated to issue a final MS4 rule by November 17, 2016, under the terms of the settlement. The agency also is required to determine by May 26, 2016, if it will regulate stormwater runoff from forest roads.

In May 2015, EPA, and the U.S. Army released the final Clean Water Rule. The rule is intended to define more precisely which waters are protected under the Clean Water Act, making determinations more predictable and, therefore, decreasing the cost and increasing the speed of the permitting process. According to EPA, the Clean Water Rule maintains the current status of MS4s and encourages the use of green infrastructure. However, the rule has come under heavy fire from industry groups, states, and congress. In October, following an injunction blocking the enforcement of the Clean Water Rule in 13 states, the Sixth Circuit of the U.S. Court of Appeals issued a nationwide stay on the rule.

TMDLs are another primary regulatory driver for stormwater management, particularly in the Chesapeake Bay. Established in 2010, the Chesapeake Bay TMDL requires reductions in nutrients and sediment from seven jurisdictions in the bay watershed. These jurisdictions developed individual plans for achieving pollutant reductions and committed to 2-year milestones. This multi-state TMDL was the subject of a lengthy court case involving The American Farm Bureau Federation and other plaintiffs. However, in 2015, the federal Third Circuit Court of Appeals upheld the legality of the TMDL, ruling in favor of EPA and other supporting states and organizations.


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A key objective of WEF’s Rainfall to results report is closing the funding gap, as this remains a primary challenge for communities across the U.S. The report calls dedicated funding sources, such as user-based stormwater fees, essential to driving community investment in stormwater management. However, such fees face legal challenges, a lack of community support, and other setbacks across the country. Despite the effects of Hurricane Katrina and Superstorm Sandy, neither Louisiana nor New York have any stormwater utilities, according to a 2014 survey by Western Kentucky University.

Yet in 2015, the Northeast Ohio Regional Sewer District won a stormwater fee victory when the state supreme court ruled that the utility is authorized to manage stormwater and can impose a fee for that purpose. Early in 2015, Maryland repealed its state-mandated stormwater fee, but new legislation still requires that counties comply with and fund federal stormwater requirements.

However, stormwater solutions can support many community priorities. The sector has a unique opportunity to advance sustainability, resiliency, and community livability. The multi-benefit nature of green infrastructure can lead to non-traditional partnerships and funding arrangements.

In April 2015, EPA Region 3 released a guide supporting community-based public-private partnerships. The guide includes a case study on the Clean Water Partnership (CWP), a community-based public-private partnership between Prince George’s County, Md., and Corvias Solutions. Through the CWP, Corvias will manage $100 million in green infrastructure projects, which are expected to be built faster and at a lower cost while boosting economic development. In fall 2015, the CWP completed its first stormwater retrofit project.

In early 2015, EPA also launched the Water Infrastructure and Resiliency Finance Center and announced a new municipal bond to encourage such public–private partnerships. Overall, green bonds like this are expected to play a larger role in helping communities fund projects that create environmental improvements and increase climate resiliency, according to the Climate Bonds Initiative.