Significant changes in water quantity and quality are evident across the country. These changes, which are expected to persist, present an ongoing risk to coupled human and natural systems and related ecosystem services. Variable precipitation and rising temperature are intensifying droughts, increasing heavy downpours, and reducing snowpack. Reduced snow-to-rain ratios are leading to significant differences between the timing of water supply and demand. Groundwater depletion is exacerbating drought risk. Surface water quality is declining as water temperature increases and more frequent high-intensity rainfall events mobilize pollutants such as sediments and nutrients.
Deteriorating water infrastructure compounds the climate risk faced by society. Extreme precipitation events are projected to increase in a warming climate and may lead to more severe floods and greater risk of infrastructure failure in some regions. Infrastructure design, operation, financing principles, and regulatory standards typically do not account for a changing climate. Current risk management does not typically consider the impact of compound extremes (co-occurrence of multiple events) and the risk of cascading infrastructure failure.
Water management strategies designed in view of an evolving future we can only partially anticipate will help prepare the Nation for water- and climate-related risks of the future. Current water management and planning principles typically do not address risk that changes over time, leaving society exposed to more risk than anticipated. While there are examples of promising approaches to manage climate risk, the gap between research and implementation, especially in view of regulatory and institutional constraints, remains a challenge.
Significant changes in water quantity and quality are evident across the country. These changes, which are expected to persist, present an ongoing risk to coupled human and natural systems and related ecosystem services. Variable precipitation and rising temperature are intensifying droughts, increasing heavy downpours, and reducing snowpack. Reduced snow-to-rain ratios are leading to significant differences between the timing of water supply and demand. Groundwater depletion is exacerbating drought risk. Surface water quality is declining as water temperature increases and more frequent high-intensity rainfall events mobilize pollutants such as sediments and nutrients.
Deteriorating water infrastructure compounds the climate risk faced by society. Extreme precipitation events are projected to increase in a warming climate and may lead to more severe floods and greater risk of infrastructure failure in some regions. Infrastructure design, operation, financing principles, and regulatory standards typically do not account for a changing climate. Current risk management does not typically consider the impact of compound extremes (co-occurrence of multiple events) and the risk of cascading infrastructure failure.
Water management strategies designed in view of an evolving future we can only partially anticipate will help prepare the Nation for water- and climate-related risks of the future. Current water management and planning principles typically do not address risk that changes over time, leaving society exposed to more risk than anticipated. While there are examples of promising approaches to manage climate risk, the gap between research and implementation, especially in view of regulatory and institutional constraints, remains a challenge.
Virtually Certain | Extremely Likely | Very Likely | Likely | About as Likely as Not | Unlikely | Very Unikely | Extremely Unlikely | Exceptionally Unlikely |
---|---|---|---|---|---|---|---|---|
99%–100% | 95%–100% | 90%–100% | 66%-100% | 33%-66% | 0%-33% | 0%-10% | 0%-5% | 0%-1% |
Very High | Hoch | Medium | Niedrig |
---|---|---|---|
Strong evidence (established theory, multiple sources, consistent results, well documented and accepted methods, etc.), high consensus | Moderate evidence (several sources, some consistency, methods vary and/or documentation limited, etc.), medium consensus | Suggestive evidence (a few sources, limited consistency, models incomplete, methods emerging, etc.), competing schools of thought | Inconclusive evidence (limited sources, extrapolations, inconsistent findings, poor documentation and/or methods not tested, etc.), disagreement or lack of opinions among experts |
Documenting Uncertainty: This assessment relies on two metrics to communicate the degree of certainty in Key Findings. See Guide to this Report for more on assessments of likelihood and confidence.
Ensuring a reliable supply of clean freshwater to individuals, communities, and ecosystems, together with effective management of floods and droughts, is the foundation of human and ecological health. The water sector is also central to the economy and contributes significantly to the resilience of many other sectors, including agriculture, energy, urban environments, and industry.
Water systems face considerable risk, even without anticipated future climate changes. Limited surface water storage, as well as a limited ability to make use of long-term drought forecasts and to trade water across uses and basins, has led to a significant depletion of aquifers in many regions in the United States.1 Across the Nation, much of the critical water and wastewater infrastructure is nearing the end of its useful life. To date, no comprehensive assessment exists of the climate-related vulnerability of U.S. water infrastructure (including dams, levees, aqueducts, sewers, and water and wastewater distribution and treatment systems), the potential resulting damages, or the cost of reconstruction and recovery. Paleoclimate information (reconstructions of past climate derived from ice cores or tree rings) shows that over the last 500 years, North America has experienced pronounced wet/dry regime shifts that sometimes persisted for decades.2 Because such protracted exposures to extreme floods or droughts in different parts of the country are extraordinary compared to events experienced in the 20th century, they are not yet incorporated in water management principles and practice. Anticipated future climate change will exacerbate this risk in many regions.
A central challenge to water planning and management is learning to plan for plausible future climate conditions that are wider in range than those experienced in the 20th century. Doing so requires approaches that evaluate plans over many possible futures instead of just one, incorporate real-time monitoring and forecast products to better manage extremes when they occur, and update policies and engineering principles with the best available geoscience-based understanding of planetary change. While this represents a break from historical practice, recent examples of adaptation responses undertaken by large water management agencies, including major metropolitan water utilities and the U.S. Army Corps of Engineers, are promising.
<b>Lall</b>, U., T. Johnson, P. Colohan, A. Aghakouchak, C. Brown, G. McCabe, R. Pulwarty, and A. Sankarasubramanian, 2018: Water. In <i>Impacts, Risks, and Adaptation in the United States: Fourth National Climate Assessment, Volume II</i> [Reidmiller, D.R., C.W. Avery, D.R. Easterling, K.E. Kunkel, K.L.M. Lewis, T.K. Maycock, and B.C. Stewart (eds.)]. U.S. Global Change Research Program, Washington, DC, USA, pp. 145–173. doi: 10.7930/NCA4.2018.CH3
Water security in the United States is increasingly in jeopardy. Ensuring a reliable supply of clean freshwater to communities, agriculture, and ecosystems, together with effective management of floods and droughts, is the foundation of human and ecological health. The water sector is also central to the economy, contributing significantly to the resilience of many other sectors, including agriculture (Ch. 10: Ag & Rural, KM 2 and 4), energy (Ch. 4: Energy), urban environments (Ch. 11: Urban), and industry. The health and productivity of natural aquatic and wetland ecosystems are also closely linked to the water sector (Ch. 7: Ecosystems, KM 1).
Changes in the frequency and intensity of climate extremes relative to the 20th century5,6 and deteriorating water infrastructure are contributing to declining community and ecosystem resilience. Climate change is a major driver of changes in the frequency, duration, and geographic distribution of severe storms, floods, and droughts (Ch. 2: Climate). In addition, paleoclimate information (reconstructions of past climate derived from ice cores or tree rings) shows that over the last 500 years, North America has experienced pronounced wet/dry regime shifts that sometimes persisted for decades.2 These shifts led to protracted exposures to extreme floods or droughts in different parts of the country that are extraordinary compared to events experienced in the 20th century. Operational principles for engineering, design, insurance programs, water quality regulations, and water allocation generally have not factored in these longer-term perspectives on historical climate variability or projections of future climate change.7,8 While there has been much discussion on the need for climate adaptation, the design and implementation of processes that consider near- and long-term information on a changing climate are still nascent.9,10,11
Water systems face considerable risk even without anticipated future climate changes. Gains in water-use efficiency over the last 30 years have resulted in total U.S. water consumption staying relatively constant.12 Gains in efficiency are most evident in urban centers.13 However, limited surface water storage and a limited ability to make use of long-term drought forecasts and to trade water across uses and basins have led to the significant depletion of aquifers in many regions of the United States.1 Aging and deteriorating dams and levees14 also represent an increasing hazard when exposed to extreme or, in some cases, even moderate rainfall. Several recent heavy rainfall events have led to dam, levee, or critical infrastructure failures, including the Oroville emergency spillway in California in 2017,15 Missouri River levees in 2017, 50 dams in South Carolina in October 201516 and 25 more dams in the state in October 2016,17 and New Orleans levees in 2005 and 2015.18 The national exposure to this risk has not yet been fully assessed.
Every region of the United States is affected by water sector sensitivities to weather- and climate-related events (see Figure 3.1). Recent examples are summarized below:
Northern and Southern Great Plains: Future changes in precipitation and the potential for more extreme rainfall events will exacerbate water-related challenges in the Northern Great Plains (Ch. 22: N. Great Plains, KM 1). Extreme precipitation and rising sea levels associated with climate change make the built environment in the Southern Great Plains increasingly vulnerable to disruption, particularly as infrastructure ages and deteriorates (Ch. 23: S. Great Plains, KM 2). Flooding on the Mississippi and Missouri Rivers in May 2011 caused an estimated $5.7 billion in damages (in 2018 dollars).19 One year later, drought conditions in 2012 led to record low flows on the Mississippi, disrupting river navigation and agriculture and resulting in widespread harvest failures for corn, sorghum, soybean, and other crops (e.g., Ziska et al. 2016).20 The nationwide total damage from the 2012 drought is estimated at $33 billion (in 2018 dollars).19
Northeast and Southeast: Much of the water infrastructure in the Northeast is nearing the end of its planned life expectancy. Disruptions to infrastructure are already occurring and will likely become more common with a changing climate (Ch. 18: Northeast, KM 3). Hurricane Irene (2011) and Superstorm Sandy (2012) highlighted the inadequacy of deteriorating urban infrastructure, including combined sewers, for managing current and future storm events.19 In the Southeast, the combined effects of extreme rainfall events and rising sea level are increasing flood frequencies, making coastal and low-lying regions highly vulnerable to climate change impacts (Ch. 8: Coastal, KM 1; Ch. 19: Southeast, KM 2). In South Carolina in 2015, locally extreme rainfall exceeding 20 inches over 3 days19 caused widespread damage, including the failure of 49 state-regulated dams, one federally regulated dam, two sections of the levee adjacent to the Columbia Canal, and many unregulated dams.16 In Louisiana in 2016, a severe large-scale storm with record atmospheric moisture dropped nearly 20 inches of rain in 72 hours, triggering widespread flooding that damaged at least 60,000 homes and led to 13 deaths.21
Midwest: Storm water management systems and other critical infrastructure in the Midwest are already experiencing impacts from changing precipitation patterns and elevated flood risks (Ch. 21: Midwest, KM 5). In addition, harmful algal blooms (HABs) in western Lake Erie have been steadily increasing over the past decade.22 Warmer temperatures and heavy precipitation associated with climate change contribute to the development of HABs.23,24 Harmful algal blooms can introduce cyanobacteria into recreational and drinking water sources, resulting in restrictions on access and use. In 2014 in Toledo, Ohio, half a million people were warned to avoid drinking the water due to toxins overwhelming a water treatment plant in Lake Erie’s western basin as a result of a harmful bloom. Conditions that encourage cyanobacteria growth, such as higher water temperatures, increased runoff, and nutrient-rich habitats, are projected to increase in the Midwest (Ch. 21: Midwest).
Northwest and Alaska: Pacific salmon populations in the Northwest are being affected by climate stressors, including low snowpack (such as in 2015), decreasing summer streamflow,25,26 habitat loss through increasing storm intensity and flooding,27,28 physiological and behavioral sensitivity, and increasing mortality due to warmer stream and ocean temperatures.29 Salmon are a cultural and ecological keystone species in this region. Salmon loss is a particular threat to the cultural identities and economies of Indigenous communities (Ch. 24: Northwest, KM 2; Ch. 15: Tribes). In Alaska, residents, communities, and their infrastructure also continue to be affected by flooding and erosion of coastal and river areas, resulting from changes in sea ice (Ch. 26: Alaska, KM 2).
Southwest: Water supplies for people and nature in the Southwest are decreasing during droughts due in part to human-caused climate change. Intensifying droughts, increasing heavy downpours, and reduced snowpack are combining with increasing water demands from a growing population, deteriorating infrastructure, and groundwater depletion to reduce the future reliability of water supplies (Ch. 25: Southwest, KM 1). The 2011–2016 California drought was characterized by low precipitation combined with record high temperatures, leading to significant socioeconomic and environmental impacts.30,31 Drought risk is being exacerbated by increasing human water use and the depletion of groundwater that serves as a buffer against water scarcity.30 Rising air temperatures may increase the chance of droughts in the western United States.31,32 Compounding the impacts of drought in February 2017, heavy, persistent rainfall across northern and central California led to substantial property and infrastructure damage from record flooding, landslides, and erosion.
U.S. Caribbean, Hawaiʻi and U.S.-Affiliated Pacific Islands: Dependable and safe water supplies for the communities and ecosystems of the U.S. Caribbean, Hawaiʻi, and the U.S.-Affiliated Pacific Islands are threatened by rising temperatures, sea level rise, saltwater intrusion, and increased risk of extreme drought and flooding (Ch. 20: U.S. Caribbean, KM 1; Ch. 27: Hawaiʻi & Pacific Islands, KM 1). The U.S. Caribbean is experiencing an increasing frequency of extreme events that threaten life, property, and the economy (Ch. 20: U.S. Caribbean, KM 5). On September 20, 2017, Hurricane Maria struck the U.S. Virgin Islands as a Category 5 storm and then Puerto Rico as a Category 4 storm—just two weeks after Hurricane Irma had struck the Caribbean islands. The storms left devastation in their wake, with the power distribution severely damaged and drinking water and wastewater treatment plants rendered inoperable.33 Maria’s extreme rainfall, up to 37 inches in 48 hours in some places,34 also caused widespread flooding and mudslides across the islands.
Climate change effects on hydrology, floods, and drought for the United States are discussed in the Climate Science Special Report35,36 and the Third National Climate Assessment.6 Increasing air temperatures have substantially reduced the fraction of winter precipitation falling as snow, particularly over the western United States.37,38,39,40,41,42 Warming has resulted in a shift in the timing of snowmelt runoff to earlier in the year.39,43,44,45,46,47 Glaciers continue to melt in Alaska25,48 and the western United States (Ch. 1: Overview, Figure 1.2d).49,50 Shifts in the hydrological regime due to glacier melting will alter stream water volume, water temperature, runoff timing, and aquatic ecosystems in these regions. As temperatures continue to rise, there is a risk of decreased and highly variable water supplies for human use and ecosystem maintenance.32,51
Additionally, heavy precipitation events in most parts of the United States have increased in both intensity and frequency since 1901 and are projected to continue to increase over this century under both a lower and higher scenario (RCP4.5 and RCP8.5; see Easterling et al. 2017, Key Finding 235). There are, however, important regional and seasonal differences in projected changes in total precipitation.
Higher temperatures also result in increased human use of water, particularly through increased water demand for agriculture arising from increased evapotranspiration (Ch. 10: Ag & Rural, KM 1).52,53 In some regions of the United States, water supplies are already stressed by increasing consumption.12 Continued warming will add to the stress on water supplies and adversely impact water supply reliability in parts of the United States. Over the last 30 years, improvements in water-use efficiency have offset the increasing water needs from population growth, and national water use has remained constant.12 However, without efforts to increase water-use efficiency in rural and urban areas, increased future demand due to warming could exceed future supply in some locations.13
In the United States, groundwater provides more than 40% of the water used for agriculture (irrigation and livestock) and domestic water supplies (Ch. 25: Southwest; Ch. 10: Ag & Rural, KM 1).1,12 Groundwater use for irrigation has increased substantially since about 1900 and in some areas has exceeded natural aquifer recharge rates.54 For example, in the High Plains Aquifer, the largest freshwater aquifer in the contiguous United States that supports an important agricultural region,55 the rate of groundwater withdrawal for irrigation is nearly 10 times the rate of natural recharge, resulting in large groundwater depletions (see Figure 3.2).56,57,58,59 Groundwater pumping for irrigation is a substantial driver of long-term trends in groundwater levels in the central United States.60,61 In many parts of the United States, groundwater is being depleted due to increased pumping during droughts and concentrated demands in urban areas.1 Increasing air temperatures, insufficient precipitation, and associated increases in irrigation requirements will likely result in greater groundwater depletion in the coming decades.62 The lack of coordinated management of surface water and groundwater storage limits the Nation’s ability to address climate variability. Management of surface water and groundwater storage and water quality are not coordinated across different agencies, leading to inefficient response to changing climate.
Changes in climate and hydrology have direct and cascading effects on water quality.63,64 Anticipated effects include warming water temperatures in all U.S. regions, which affect ecosystem health (Ch. 7: Ecosystems), and locally variable changes in precipitation and runoff, which affect pollutant transport into and within water bodies.6,65 These changes pose challenges related to the cost and implications of water treatment, and they present a risk to water supplies, public health, and aquatic ecosystems. Increases in high flow events can increase the delivery of sediment,66,67,68 nutrients,69,70,71,72 and microbial pathogens23,73 to streams, lakes, and estuaries; decreases in low flow volume (such as in the summer) and during periods of drought can impact aquatic life through exposure to high water temperatures and reduced dissolved oxygen.74,75,76 The risk of harmful algal blooms could increase due to an expanded seasonal window of warm water temperatures and the potential for episodic increases in nutrient loading.23,24,77 In coastal areas, saltwater intrusion into coastal rivers and aquifers can be exacerbated by sea level rise (or relative sea level rise related to vertical land movement) (Ch. 1: Overview, Figure 1.4), storm surges, and altered freshwater runoff. Saltwater intrusion could threaten drinking water supplies, infrastructure,78 and coastal and estuarine ecosystems (Ch. 8: Coastal).79,80 Indirect impacts on water quality are also possible in response to an increased frequency of forest pest/disease outbreaks, wildfire, and other terrestrial ecosystem changes; land-use changes (for example, agricultural and urban) and water management infrastructure also interact with climate change to impact water quality.
Across the Nation, much of the critical water infrastructure is aging and, in some cases, deteriorating or nearing the end of its design life, presenting an increased risk of failure . Estimated reconstruction and maintenance costs aggregated across dams, levees, aqueducts, sewers, and water and wastewater treatment systems total in the trillions of dollars based on a variety of different sources.14,81,82,83,84,85,86,87 Capital improvement needs for public water systems (which provide safe drinking water) have been estimated at $384 billion for projects necessary from 2011 through 2030.88 Similarly, capital investment needs for publicly owned wastewater conveyance and treatment facilities, combined sewer overflow correction, and storm water management to address water quality or water quality-related public health problems have been estimated at $271 billion over a 20-year period.89 More than 15,000 dams in the United States are listed as high risk85 due to the potential losses that may result if they failed.
Extreme precipitation events are projected to increase in a warming climate and may lead to more severe floods and greater risk of infrastructure failure in some regions.90 Long-lasting droughts and warm spells can also compromise earth dams and levees as a result of the ground cracking due to drying, a reduction of soil strength, erosion, and subsidence (sinking of land).91,92 To date, however, there is no comprehensive assessment of the climate-related vulnerability of U.S. water infrastructure, and climate risks to existing infrastructure systems remain unquantified. Tools, case studies, and other information are available that can be adopted into design standards and operational guidelines to account for future climate and/or integrate climate projections into infrastructure design (e.g., EPA 2016, Ragno et al. 2018;90,93 see also Key Message 3). However, there are no common design standards or operational guidelines that address how infrastructure should be designed and operated in the face of changing climate risk or that even target the range of climate variability seen over the last 500 years.
Procedures for the design, estimation of probability of failure, and risk assessment of infrastructure rely on 10–100 years of past data about flood and rainfall intensity, frequency, and duration (e.g., Vahedifard et al. 201715). This approach assumes that the frequency and severity of extremes do not change significantly over time.94 However, numerous studies suggest that the severity and frequency of climatic extremes, such as precipitation and heat waves, have, in fact, been changing.5,14,25,95,96,97,98,99 These changes present a regionally variable risk of increased frequency and severity of floods and drought.6,36 In addition, tree ring reconstructions of climate over the past 500 years for the United States illustrate a much wider range of climate variability than does the instrumental record (which begins around 1900).100,101,102 This historical variability includes wet and dry periods with statistics very different from those of the 20th century. Infrastructure design that uses recent historical data may thus underrepresent the risk seen from the paleo record, even without considering future climate change. Statistical methods have been developed for climate risk and frequency analysis that incorporate observed and/or projected changes in extremes.90,94,103,104,105 However, these procedures have not yet been incorporated in infrastructure design codes and operational guidelines.
Compound extreme events—the combination of two or more hazard events or climate variables over space and/or time that leads to an extreme impact—have a multiplying effect on the risk to society, the environment, and built infrastructure.106 Recent examples include the 2016 Louisiana flood, which resulted in simultaneous flooding across a large area (Ch. 19: Southeast, KM 2 and Table 19.1);21 Superstorm Sandy in 2012, when extreme rainfall coincided with near high tides;107 and other events combining storm surge and extreme precipitation, such as Hurricane Isaac in 2012 and Hurricane Matthew in 2016. Traditional infrastructure design approaches and risk assessment frameworks often consider these drivers in isolation. For example, current coastal flood risk assessment methods consider changes in terrestrial flooding and ocean flooding separately,108,109,110,111,112 leading to an underestimation or overestimation of risk in coastal areas.112 Compound extremes can also increase the risk of cascading infrastructure failure since some infrastructure systems rely on others, and the failure of one system can lead to the failure of interconnected systems, such as water–energy infrastructure (Ch. 4: Energy; Ch. 17: Complex Systems).113
The susceptibility of society to the harmful effects of hydrologic variability and the implications of climate variability and change necessitate a reassessment of the water planning and management principles developed in the 20th century. Significant changes in many key hydrologic design variables (including the quantity and quality of water) and hydrologic extremes are being experienced around the Nation. Paleoclimate analyses and climate projections suggest persistent droughts and wet periods over the continental United States that are longer, cover more area, and are more intense than what was experienced in the 20th century. An evolving future, which can only be partially anticipated, adds to this risk. Furthermore, while hydroclimatic extremes are projected to increase in frequency, accurate predictions of changes in extremes at a particular location are not yet possible. Instead, climate projections provide a glimpse of possible future conditions and help to scope the plausible range of changes.
A central challenge to water planning and management is learning to plan for plausible future climate conditions that are wider in range than those experienced in the past (see Figure 3.3) (see also Ch. 28: Adaptation, KM 5). Doing so requires approaches that evaluate plans over many possible futures instead of just one, incorporate real-time monitoring and forecast products to better manage extremes when they occur, and update policies and engineering principles with the best available geoscience-based understanding of global change. The challenge is both scientific, in terms of developing and evaluating these approaches, and institutional–political, in terms of updating the regulatory–legal and institutional structures that constrain innovation in water management, planning, and infrastructure design.
One approach is to focus on better managing variability, which is likely the dominant source of operational uncertainty for many water systems.115 An example of this approach is incorporating monitoring of current conditions and forecasts of near-term future conditions (days to weeks to seasons) in lieu of stationary operating rules based on historical expectations. Forecasts of near-term hydrologic conditions can provide the basis for adaptive reservoir operations, but they require flexible operating rules. New York City, for example, altered existing operational guidelines to implement adaptive reservoir operations based on current hydrologic conditions to better meet new concerns for ecological flow requirements in addition to water supply goals.116 In another example, the International Joint Commission adopted a new operating plan for Upper Great Lakes water levels; the plan is based on the ability to provide acceptable performance, as defined by stakeholders, over thousands of possible future climates.117 The plan includes forecast-based operations and a funded adaptive management process linking observatories and information systems to water-release decisions to address unanticipated change.118 In addition, updating operations and optimizing for changing conditions as they occur provide additional operating flexibility for water supply, flood risk reduction, and hydropower reservoirs.119,120,121 Finally, financial instruments and water trading provide avenues for managing the effects of variability on water competition, especially between urban water supply and agricultural water use.122,123,124
Better management of variability does not eliminate the need for long-term planning that responds to plausible climate changes (see Figure 3.3). Major water utilities provide examples of planning that focus on identifying and managing vulnerabilities to a wide range of uncertain future conditions, rather than evaluating performance for a single future.125 For example, Tampa Bay Water employed 1,000 realizations of future demand and future supply to evaluate their preparedness for future conditions.126 Alternatively, Denver Water used a small set of carefully selected future climate and socioeconomic development scenarios to explore possible future vulnerabilities.125 The World Bank published a set of specific guidelines for implementing such robustness-based approaches in water investment evaluation.127 As described in Key Message 2, the nature of hydrologic extremes and their rarity complicate the detection of meaningful trends in flood risk,128 while traditional trend detection methods may lead to missed trends and underpreparation.129 In response to these challenges, the U.S. Army Corps of Engineers is exploring robustness to a wide range of trends and expected regret as metrics for evaluating flood management strategies,130,131 including the increased incorporation of natural infrastructure.132
Actions taken by communities and the managers of water systems of all sizes can help prepare the Nation for the water-related risks of climate variability and change. The risks associated with a changing climate are compounded by inadequate attention to the state of water infrastructure and insufficient maintenance. Developing new water management and planning approaches may require updating the regulatory, legal, and institutional structures that constrain innovation in water management, community planning, and infrastructure design.133,134 Furthermore, adequate maintenance and sufficient funding to monitor, maintain, and adapt water policy and infrastructure would help overcome many of these challenges. Continued collaboration on transboundary watershed coordination and agreements on both surface water and groundwater with Canada and Mexico are among the actions that could facilitate more sustainable binational water management practices.
Developing and implementing new approaches pose special challenges for smaller, rural, and other communities with limited financial and technical resources. The development and adoption of new approaches can be facilitated by assessments that compare the effectiveness of new management and planning approaches across regions; greater exchange of emerging expertise among water managers; and better conveyance of the underlying climate and water science to communities, managers, and other decision-makers.135,136
Chapter authors were selected based on criteria, agreed on by the chapter lead and coordinating lead authors, that included a primary expertise in water sciences and management, knowledge of climate science and assessment of climate change impacts on water resources, and knowledge of climate change adaptation theory and practice in the water sector.
The chapter was developed through technical discussions and expert deliberation among chapter authors, federal coordinating lead authors, and staff from the U.S. Global Change Research Program (USGCRP). Future climate change impacts on hydrology, floods, and drought for the United States have been discussed in the Third National Climate Assessment6 and in the USGCRP’s Climate Science Special Report.35,36 Accordingly, emphasis here is on vulnerability and the risk to water infrastructure and management presented by climate variability and change, including interactions with existing patterns of water use and development and other factors affecting climate risk. The scope of the chapter is limited to inland freshwater systems; ocean and coastal systems are discussed in their respective chapters in this report.