Introduction
Sustainable management of urban water supply, stormwater, and wastewater, is critical to the health and well-being of people in urban areas, and to ecosystems affected by urban land and water use. The demands of population growth, aging infrastructure and changing climate will increase pressure on all of these systems in the future. Here, we describe an approach that builds on the concept of the city blueprint (a framework to assess urban water sustainability of cities globally) to identify vulnerabilities in the urban water system at the spatial extent of entire cities, and then uses multi-scale design and evaluation of alternative future scenarios to explore and inform decision makers of the potential outcomes of different options. Our approach uses basin-scale modeling to characterize the regional context for the scenarios. Finer-scale modeling and evaluation of the scenarios at the spatial extent of watersheds and urbanizing neighborhoods is used to evaluate options and provide information to managers at scales relevant to their decision-making needs.“Harvesting experience (i.e., systematically and rigorously validating and documenting examples of success in Sustainable Urban Water Management) is needed to build a robust evidence base for the implementation of “what has already worked” in new locations so that resources can be directed toward appropriate adaptation to local contexts rather than wholesale reinvention.”J. Hering and K. Vairavamoorthy (2018)
Building collaborations for the future: identifying priorities in transdisciplinary projects
“Alone we can do so little, together we can do so much.”Helen Keller (Lash 1980)
Sector | Overarching system goals | Key elements of a well-performing system | Opportunities provided by integration |
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Drinking water | Public health; adequate water supply for population, reliable system of treatment and delivery | Adequate source water protection, treatment facilities, distribution network Capacity to meet future demands (resilient to climate change, population change) Infrastructure and source resilient to disruption from natural disasters/other emergencies Efficient (minimal water loss through leaks; minimal energy use) Meets social needs in a just and equitable manner | Stormwater or wastewater reuse lower water supply needs, and could reduce treatment and conveyance costs and minimize ecosystem impacts of withdrawals and infrastructure |
Stormwater | Public and ecosystem health; protection from localized flooding, reduced pollution from non-point sources | Conveys water away from buildings and infrastructure Prevents flooding, even during low frequency, extreme events Minimizes water quality/quantity impacts of stormwater runoff on riparian areas and water bodies | Effective treatment of stormwater improves water quality and function of natural streams/other water bodies Storm water becomes a resource in a “fit-for-purpose” reuse or for groundwater recharge |
Wastewater | Public and ecosystem health; removal and treatment of human and industrial wastewater prior to release into natural waterbodies | Conveys sewage and waste away from dwellings/infrastructure Recycles sewage solids Minimizes water quality/quantity impacts of discharge to surface water (ideally with secondary and/or tertiary treatment) Minimizes combined sewer overflows Capacity to meet future demands (population change) Efficient Resilient to disruption from natural disasters/other emergencies Meets social needs in a just and equitable manner | Some components of wastewater can become resources (e.g., struvite as fertilizer) Grey water put to “fit-for-purpose” reuse Reducing wastewater volumes could reduce treatment costs or provide added capacity for population growth Tertiary treatment areas (e.g. wetlands) provide recreational/ecological benefits |
Natural waterbodies (riparian zones) | Public and ecosystem health; protect communities from flooding, minimize development impacts on riparian areas and water bodies | Community planning accounts for flood risks Maintains wetlands/riparian areas to provide habitat, mitigate flood risks Manages sediment regime/hydrology to minimize impact on stream habitat, and water quality | Protected riparian zones provide for co-benefits such as reducing the urban heat island effect, providing wildlife habitat, or tertiary treatment of wastewater and stormwater |
Water system challenges and barriers to integrated solutions | Potential solutions | ||
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National UWIN Themes | PNW UWIN Themes | National UWIN Themes | PNW UWIN Themes |
Climate change Water supply reliability Population change | Hotter drier summers = greater demand, reduced supply Growth of urban areas footprint/intensity Wildfire in source water areas Competing summer water demands – instream needs for endangered fish, agriculture, growing cities | Increase social/human capital (including behavioral and institutional change) | Behavioral conservation advances (public education) Tools to inform public about conservation Changes to allocation of stored water in the Willamette Project (federal reservoir system) Regional cooperation – “One Water” mindset Collaboration around development and decision making across sectors Integrated planning and sophisticated information to inform decisions |
Water quality concerns Natural systems | Habitat degradation (nutrients, toxics, thermal pollution) Regulatory requirements Groundwater overdraft | ||
Institutional challenges | Multiple jurisdictions, multiple regulatory authorities, intersecting laws Lack of incentives for collaboration Complicated water rights | Implement decentralized solutions | Technological conservation (smart irrigation controllers, toilet rebates, fix leaks) |
Knowledge limitations | Lack of acceptance of water efficiency Water management taken for granted Uncertainty about future | Increase natural capital | Green infrastructure – integrating urban and natural systems for multiple benefits |
Economics (funding) | Rate concerns, lack of public awareness on water systems, limited willingness to pay Lack of funds for education, especially small water providers Competing demands for limited funding Speculative activity on water (new ag users) | Increase financial capital | Opportunistic collaboration across sectors and between cities and exurban upstream watershed protection Water quality trading |
Technology needs Infrastructure | Age of infrastructure, lack of funds for maintenance, backlog of defined maintenance, leaks Energy use associated with moving water between multiple disconnected systems | Implement centralized solutions (manmade capital) | Water reuse Increase environmentally sensitive water storage alternatives |
Hazards | Seismic preparedness Security Development in riparian areas |
Current Course ca. 2060 | Stressed Resources ca. 2060 | Integrated Water Future ca. 2060 | |
Scenario theme | Current regulatory regime remains in force. | Water treatment and conveyance systems are stressed. | Water quality and quantity are managed at the watershed extent. |
Pressures & Trends | |||
Climatei | Midrange of climate change projections; 2.5 °C increase in annual mean temperature (MIROC5 RCP8.5) | High end of climate change projections; 4.0 °C increase in annual mean temperature (HadGEM2-ES RCP8.5) | High end of climate change projections; 4.0 °C increase in annual mean temperature (HadGEM2-ES RCP8.5) |
Population growthi | Midrange population increase; Willamette Basin 2060 population is 4.5 M (from 2.4 M in 2010) | High population increase; Willamette Basin 2060 population is 6.2 M; 37% increase relative to Current Course | High population increase; Willamette Basin 2060 pop is 6.2 M; 37% increase relative to Current Course |
Key Concerns | Basin Extent - Scenario Assumptions (Willamette River Basin) | ||
Wildfire suppression | Wildfire suppression at historical rates; forest area burned averages 0.5% of forested area in basin per year over the modeled period. | Increase in wildfire suppression so that forest area burned averages 1.4% of forested area in basin per year over the modeled period. | Change forest management to reduce wildfire, thus increasing wildfire suppression, so that forest area burned averages 0.95% of forested area in basin over the modeled period. |
Agricultural water demand | Crop mixes similar to 2010; crop and energy prices do not rise in real terms; result is about 111,000 ha irrigated. Average fraction of water rights used in a given year is 2/3 of existing irrigation water rights. | New irrigation contracts and related rights introduced 2015–2044. Conveyance costs decrease through efficiencies; water contract fees set to zero; crop choice as in Current Course. Average fraction of water rights used in a given year is 5/6 of existing irrigation water rights. | New irrigation contracts and related rights introduced 2015–2044. Conveyance costs decrease through efficiencies; contract fees set to zero; crop choice as in Current Course. Average fraction of water rights used in a given year is 2/3 of existing irrigation water rights. |
Reservoir management | Rule curves implemented as of 2011; reservoir refill begins Feb 1 with target to fill reservoirs by May. No new water rights and no new deliveries of stored water from reservoirs. | Reservoir refill begins March 1, ramps up to existing rule curves between March and May; 2% chance each year for one of the five biggest reservoirs to go offline for one calendar year; reservoir treated as “Run of the River” when offline. New claims of stored water (May–October) up to 197 M cubic meters for municipal uses, up to 404 M cubic meters for agricultural irrigation. | Reservoir refill begins March 1, ramps up to existing rule curves between March and May. New claims of stored water (May–October) up to 197 M cubic meters for municipal uses, up to 404 M cubic meters for agricultural irrigation. |
Key Concerns | Watershed Extent – Scenario Assumptions (Chicken Creek Watershed) | ||
Healthy streams; Flood protection | Current practices and policies continue. | Because storm water management relies more on conventional grey infrastructure than is the case in Current Course, the area of impervious surface is greater than in Current Course. | Because storm water management relies more on green infrastructure than Current Course, pervious surface is increased relative to Current Course. Subsidies encourage higher home densities and reduced building footprints, reducing area of impervious surface. |
Management of riparian zones and watershed land management | Within urbanized areas, width of protected riparian zones current policies and development patterns. In newly urbanizing and designated rural areas, METRO regional government guidelines for riparian protection zones apply. | Development occurs in riparian areas that are protected in the Integrated Water future. Ten percent of METRO-designated riparian protection zones are developed. | All riparian corridors are protected. Floodplain reconnection and large GI features created where topography and soils are appropriate. Rural land is purchased prior to inclusion in urban growth areas. Base flows and channel forming flows are maintained at adequate volumes. |
Role of stormwater reclamation & reuse | BMPs are used in MS4 areas and include water reuse. Downspouts disconnection allows 80% of storm water to be infiltrated on site. | Storm water management relies more on grey infrastructure than is the case in Current Course. | Storm water is more commonly reclaimed and reused in newly urbanized territory, thereby reducing water demand on other systems. 100% of stormwater is captured on-site. |
Water conservation & reuse | 50% of households are high efficiency indoor water users (424 l per household per day); 50% of households are moderate efficiency (522 lphd). Moderate adoption of xeriscaping and high efficiency irrigation systems. Greywater is not reused. | 100% of households are moderate efficiency indoor water users (522 lphd). Outdoor water conservation practices remain unchanged since 2010. Greywater is not reused. Stormwater is not reused. | 90% of households are high efficiency indoor water users (424 lphd); 10% of households are moderate efficiency (522 lphd). Aggressive adoption of xeriscaping and high efficiency irrigation systems. Moderate adoption of graywater reuse for toilet flushing with 757 l per household (200 gph) storage. Aggressive adoption of stormwater capture and reuse for irrigation with 11,356 l per household (3000 gph) storage. |
Number of households | 3629 new households are added by ca. 2060, 1218 in the Sherwood Neighborhood and 2411 outside of it, in addition to 84 new rural dwellings. | 6107 new households are added by ca. 2060, 1610 in the Sherwood Neighborhood and 4497 outside of it, in addition to 115 new rural dwellings. | 5919 new households are added by ca. 2060, 1494 in the Sherwood Neighborhood and 4425 outside of it. Approximately 115 rural dwellings are added, with 15% in clustered configurations. |
Key Concerns | Neighborhood Extent – Scenario Assumptions (Sherwood Neighborhood Focal Area) | ||
Stormwater management; green infrastructure (GI) | 32 ha of GI in the Sherwood Neighborhood focal area by ca. 2060, 28% of area. GI facilities employed only within urbanized territory. | 16 ha of GI in the Sherwood Neighborhood focal area by ca. 2060, 14% of area, no new GI facilities installed after 2030. GI facilities employed only within urbanized territory. | 55 ha of GI in the Sherwood Neighborhood focal area by ca. 2060, 48% of area. BMPs extend beyond neighborhoods under development and are integrated with watershed management systems. |
Number of households; residential density | 1218 households sited avoiding narrow riparian lands and steep slopes. Total impervious cover = 63%. | 1610 households sited avoiding narrow riparian lands and steep slopes. Total impervious cover = 72%. | 1494 households sited at higher density than in Current Course, avoiding all riparian lands, steep, and forested lands. Total impervious cover = 55%. |
Field testing the future: Designing innovative, multi-scale alternative futures
Scenario-driven alternative futures analysis is an approach to anticipatory assessments designed to inform community decisions about the likely effects of different options for future land and water use (Santelmann et al. 2001; Hulse et al. 2004; Liu et al. 2007; Mahmoud et al. 2009; Steinitz 2012; Wu et al. 2015, Rastandeh 2015). The primary advantage of this approach is as an integrative procedure for connecting the different ways of understanding the processes that shape landscapes. These range from the biophysical processes in the disciplinary realm of the sciences and engineering to the social policy and management decisions that influence land and water use. While the specific characteristics of scenario-driven alternative future studies are as diverse as the situations in which they are applied, common qualities arise. These studies begin by defining discrete, coherent assumptions about how conditions of interest unfold in some bounded place over some specified period of time. A logically coherent group of these assumptions comprise a scenario (Wodak and Neale 2015; IPBES 2016). For many scenario studies it suffices to represent scenarios with narrative descriptions alone, but, in our usage, a spatially-explicit representation of a scenario’s land and water use at temporally-explicit time steps comprise an alternative future.“Premier among the consequences of being human is the capacity to imagine possible futures, and to plan and choose among them.”E. O. Wilson (2014)
Defining the roles of stakeholders and experts
Highlights of the Willamette River Basin alternative futures effort
The alternative futures
Current course ca. 2060
Stressed resources ca. 2060
Integrated water future ca. 2060
Current course ca. 2060 | Stressed resources future ca. 2060 | Integrated water future ca. 2060 | |
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Basin scale | |||
Cumulative forest area burned1 (2010–2060) | 5012 km2 (25% of forested area) | 14510 km2 (71% of forested area) | 9435 km2 (46% of forested area) |
Watershed scale | |||
New dwelling units | 3629 | 6107 | 5919 |
Developed land area (% change from 2010) | 1370 ha (36%) | 1558 ha (55%) | 1376 ha (37%) |
Watershed imperviousness (% change from 2010)2 | 18.3% (28%) | 20.3% (42%) | 18.9% (33%) |
Protected land area (% change from 2010) | 649 ha (51%) | 390 ha (−10%) | 1332 ha (209%) |
Proportion of native bird habitat abundance at risk3 | 2.0% | 3.3% | 1.2% |
Neighborhood scale | |||
Percent low/med/high density dwellings | 36%/28%/36% | 56%/0%/44% | 0%/57%/43% |
Neighborhood imperviousness | 63% | 72% | 55% |
Green infrastructure (% of neighborhood) | 32 ha (28%) | 16 ha (14%) | 55 ha (48%) |
Simulating the future: modeling across scales
While the national UWIN stakeholder meetings helped identify general stakeholder concerns about the future of urban water management, the subsequent alternative futures process helped the Pacific Northwest stakeholders articulate those concerns with specificity, and group them into thematic, regionally plausible narratives. The next step to make the scenarios meaningful in a decision-making context, is to use evaluative models to compare and contrast the water management outcomes of the three alternative futures. Integrated evaluative models provide a tool for both pragmatic exploration of alternatives and theory building (Bach et al. 2014; Seppelt et al. 2009). When planners and decisions makers are involved, integrated models can become a tool for communities to ask “what if” questions about the future, and to articulate and visualize information helpful for long-range planning (Hulse et al. 2004; Nassauer and Opdam 2008; Steinitz 2012). In this section of the paper we highlight two challenges for modeling integrated UWS that are illustrated by this case study.“Creativity of nature and human creativity cannot be separated. But creativity implies surprises: David of Michelangelo or relativity theory. Uncertainty and surprise are part of human destiny.”Ilya Prigogine (2005)