Navigating cross-scalar challenges in adapting to climate change: insights from water planning in the Phoenix Metropolitan Area

Schulze, Paul; Meerow, Sara Article — Published Version Navigating cross-scalar challenges in adapting to climate change: insights from water planning in the Phoenix Metropolitan Area Mitigation and Adaptation Strategies for Global Change Provided in Cooperation with: Springer Nature Suggested Citation: Schulze, Paul; Meerow, Sara (2025) : Navigating cross-scalar challenges in adapting to climate change: insights from water planning in the Phoenix Metropolitan Area, Mitigation and Adaptation Strategies for Global Change, ISSN 1573-1596, Springer Netherlands, Dordrecht, Vol. 30, Iss. 7, https://doi.org/10.1007/s11027-025-10246-5 This Version is available at: https://hdl.handle.net/10419/330236 Standard-Nutzungsbedingungen: Die Dokumente auf EconStor dürfen zu eigenen wissenschaftlichen Zwecken und zum Privatgebrauch gespeichert und kopiert werden. 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If the documents have been made available under an Open Content Licence (especially Creative Commons Licences), you may exercise further usage rights as specified in the indicated licence. https://creativecommons.org/licenses/by/4.0/ ORIGINAL ARTICLE Received: 15 October 2024 / Accepted: 21 July 2025 / Published online: 14 October 2025 © The Author(s) 2025 Paul Schulze [email protected] 1 Geography Department, Humboldt-Universität zu Berlin, Rudower Chaussee 16, 12489 Berlin, Germany 2 School of Geographical Sciences and Urban Planning, Arizona State University, Tempe, USA 3 Present address: Department of Geography, University of Bonn, Meckenheimer Allee 166, 53115 Bonn, Germany Navigating cross-scalar challenges in adapting to climate change: insights from water planning in the Phoenix Metropolitan Area PaulSchulze1,3 · SaraMeerow2 Mitig Adapt Strateg Glob Change (2025) 30:65 https://doi.org/10.1007/s11027-025-10246-5 Abstract Urban regions globally face increasing challenges in maintaining robust, reliable, and sustainable water systems in light of growing climatic and institutional uncertainties. Droughtinduced supply reductions are increasingly concerning, particularly in arid regions such as the southwestern United States. This study critically examines adaptive water planning in the Phoenix Metropolitan Area (PMA) municipalities, focusing on the susceptibility of Colorado River water supplies. Drawing on a literature review and in-depth interviews with water planners, we identify and analyze key adaptation strategies, focusing on their perceived relevance, implementation dynamics, and socio-political constraints. Demand reduction, water reuse and recycling, and the recovery of stored water credits emerge as central, albeit unevenly pursued, strategies, each playing out across different spatial and temporal scales. However, our findings highlight that local adaptation planning in the PMA is shaped and constrained by persisting growth paradigms, institutional fragmentation, and complex basin-wide hydroclimatic and political uncertainties surrounding climate change impacts, overuse, and the 2026 renegotiation of Colorado River operations. While PMA municipalities benefit from diversified water portfolios, we argue that more anticipatory and transformative planning approaches and adaptation strategies are necessary to navigate and adapt to increasingly compound and cross-scalar water risks. Keywords Urban water planning · Climate change adaptation · Uncertainty · Adaptation strategies · Cross-scalar challenges 1 3 Mitigation and Adaptation Strategies for Global Change (2025) 30:65 1 Introduction Safeguarding robust, reliable, and sustainable water systems is a critical challenge for urban areas worldwide. While water planners must navigate socio-technical system dynamics, resource variability, and land use and demand trajectories (Hurlimann and Wilson 2018; Hjorth and Madani 2023; Crozier et al. 2024), future uncertainties are significantly exacerbated by the impacts of anthropogenic-induced climate change (Kundzewicz et al. 2018; Asif et al. 2023). Complex, multi-scalar water risks, such as drought-induced supply shortages, are of increasing concern, particularly in arid and high-consumptive regions such as the southwestern United States (US) (Udall and Overpeck 2017; Schmidt et al. 2023). In this context, traditional, western-centric, and engineering-oriented planning approaches rooted in assumptions of stationarity are increasingly seen as inadequate for addressing long-term uncertainties and increasingly complex water system challenges (Milly et al. 2008; Hui et al. 2018). Instead, scholars call for more adaptive and dynamic paradigms capable of navigating a “predictably unpredictable” world (Hjorth and Madani 2023, p. 2265, see also Pahl-Wostl 2015; Macpherson et al. 2024). Integrating the framework of Climate Change Adaptation Planning (CCAP) into water management is argued to better equip planners to anticipate and respond to future risks over extended temporal and spatial scales (Hurlimann and Wilson 2018; Kauffman and Hill 2021; Vinagre et al. 2023). A central aspect of CCAP involves identifying and implementing structural, institutional, ecological, or behavioral adaptation strategies tailored to local conditions (Stults and Woodruff 2017; Meerow & Woodruff 2020; Kauffman and Hill 2021). In urban settings, where water provision is often governed by utilities, public–private partnerships, and regional or state institutions (Wiechman et al. 2024), the development and effective implementation of such strategies require institutional flexibility and anticipatory capacity (Pahl-Wostl 2006; Olmstead 2014; Moore et al. 2024). However, planners must also navigate socio-political and technical constraints such as budgetary limitations, path dependencies, and the complex interplay of scales where hydroclimatic uncertainties and aspects of power and governance shape water outcomes (Olmstead 2014; Meerow and Mitchell 2017; Macpherson et al. 2024). The Phoenix Metropolitan Area (PMA) exemplifies such tensions. Situated in the arid southwestern US, the region depends on a diverse water portfolio, including water from the Colorado River conveyed via the Central Arizona Project (CAP). However, prolonged drought, streamflow declines, and overallocation of river resources have increased pressure on the Colorado River water supply (Dettinger et al. 2015; Schmidt et al. 2023). Arizona’s CAP water holds junior priority1 within the basin allocation scheme, and recent shortage declarations have triggered a 30% reduction in the state’s CAP deliveries (Kuhn and Fleck 2019; CAP 2024). Moreover, current basin operation guidelines expire in 2026, and it is uncertain what allocations Arizona will receive in the upcoming interstate negotiations (commonly termed ‘Reconsultation’) for post-2026 Colorado River operations (Kuhn and Fleck 2022; USBR 2023). 1 Junior priority water rights holders are entitled to conditionally divert and use water out-of-priority that more senior contract holders leave in the system. This is part of the Prior Appropriation System of water rights in the Southwestern US, commonly termed “First in Time, First in Right” (see: h t t p s : / / c o l o r a d o r i v e r s c i e n c e . o r g / W a t e r _ l a w _ a n d _ p o l i c y). 1 3 65 Page 2 of 25 Mitigation and Adaptation Strategies for Global Change (2025) 30:65 As the municipal CAP supplies in Central Arizona has a higher priority than that of other users, especially agriculture, most cities in the PMA have been unaffected or only minimally2 affected by the state’s CAP supply reduction (Gastélum and Cullom 2013; Arizona Water Blueprint 2024). However, we argue that the complex hydroclimatic and hydropolitical mélange raises ever-more pressing questions about long-term CAP supply reliability, which can be defined as the municipal’s water planning problem. As future shortages loom, there is an increasing need for new planning approaches and adaptive strategies that can help municipalities navigate uncertainties and potential future water gaps, defining the water planning aim. Such strategies must respond to hydroclimatic uncertainty as well as the institutional, political, and spatial configurations that shape water governance in the region (see also Rivera-Torres and Gerlak 2021). Owing to its historically unsustainable water planning regime, the PMA has received considerable scholarly attention (e.g., Bolin et al. 2010; Gober et al. 2010; Larson et al. 2013b). However, existing studies on adaptation strategies in the regional water management systems tend to focus on specific options, such as water conservation (Larson et al. 2009; Chhetri 2011) or outdoor water use (Yang and Wang 2017; Wang et al. 2021; Wang and Vivoni 2022); or single municipalities, such as Richter and colleagues’ (2013) study on conservation and water recycling strategies for the City of Phoenix. Others have examined the relationship between land-use change and water demand (Sampson et al. 2020; Gilman and Wu 2024) or the need for integrated land-water planning (Gober et al. 2013). Little is known about how water planners assess and prioritize adaptation strategies in practice or how their choices are shaped by institutional and budgetary constraints, planning paradigms, and the multi-scalar challenges of the Colorado River Basin. This study addresses that gap. Bridging adaptation research and critical urban studies, we examine how water planners in PMA municipalities approach adaptation in the face of future CAP supply susceptibility, paying particular attention to how institutional, socio-political, economic, and spatial conditions mediate their strategy choices. Through a qualitative, in-depth case study grounded in expert interviews and literature review, we aim to (i) shed light on how CAPrelated uncertainties influence municipal water planning in the PMA; and (ii) contribute to broader debates on the challenges of implementing anticipatory and adaptive planning as well as specific adaptation strategies in urban water systems in light of the cross-scalar challenges that urban water planners face in the 21st century. 2 Urban planning for climate change adaptation Climate Change Adaptation Planning (CCAP) can be conceptualized as an iterative threestage process of adaptive planning, action, and management (Fig. 1). In the adaptive action stage, appropriate technical, physical, behavioral, and procedural strategies are identified, scheduled across time, and implemented through adaptation projects (Carter et al. 2015; Meerow and Woodruff 2020; Kauffman and Hill 2021). Such actions can be further classified by intent, timing, temporal scope, spatial scope, and actors involved (Hurlimann and Wilson 2018; Kauffman and Hill 2021). The development of a set of strategies is 2 As part of the contingency measures to stabilize the water level of Lake Mead, some municipalities have voluntarily waived some portion of their CAP entitlements and supplies (in exchange for financial compensation) (CAP 2024). 1 3 Page 3 of 25 65 Mitigation and Adaptation Strategies for Global Change (2025) 30:65 recommended (Kundzewicz et al. 2018; Roach et al. 2018) and should ideally leverage co-benefits such as climate change mitigation (Meerow and Woodruff 2020). Note that ‘strategies’ is often used interchangeably with actions, interventions, measures, options, or responses. In water planning, which is commonly understood as matching supply with socioeconomic demand while addressing environmental sustainability (Walmsley and Pearce 2010; Herman et al. 2020), integrating CCAP allows anticipation of long-term uncertainties and nonstationary trends over long time horizons (Diaz and Yeh 2014; Hui et al. 2018). Adaptation strategies are typically supplyor demand-oriented and aim to reduce potential future water gaps, that is, the difference between supplies and demand (Roach et al. 2018; Straatsma et al. 2020; Elgendy et al. 2024). Such strategies should contribute to the development of robust and resilient water systems. These systems are characterized by the proper management of resources and demand to ensure long-term sustainability, maintain services even in emergency situations, anticipate the impacts of climate change, and meet stakeholder expectations (Stults and Woodruff 2017; Lyle et al. 2023; Elgendy et al. 2024). Local governments and water utilities are at the forefront of adaptation planning. Regional climate variability necessitates spatially distinct responses (Diaz and Yeh 2014; Meerow and Woodruff 2020; Kauffman and Hill 2021), and local governments are responsible for responding to extreme events, mitigating climate impacts, weighing tradeoffs, setting policy goals, mediating between stakeholders, and managing the logistics of adaptation, including infrastructure investment (Gober et al. 2010; Measham et al. 2011; Diaz and Yeh 2014; Olmstead 2014; Nordgren et al. 2016; Kauffman and Hill 2021). However, urban planners are required to navigate a high degree of uncertainty in both hydroclimatic systems and policy landscapes while balancing socioeconomic conditions, environmental trade-offs, and regulatory oversight (Meerow and Woodruff 2020; Stults and Larsen 2020; Obringer and White 2024). Planning involves complex relationships among multiple actors, and decisions often hinge on socio-political boundary conditions and public perception, making CCAP a political process (Eriksen et al. 2015; Meerow and Mitchell 2017; Macpherson et al. 2024). Scale dependencies, a key feature of urban planning in general (Seto et al. 2017), add to these endogenous water planning challenges. Given the ‘fluid’, transboundary nature of water flow, many cities depend on cross-scalar flows, such as supply sources in mountainous headwaters far beyond cities’ administrative borders (Adger et al. 2005; Straatsma et al. 2020). Spatio-temporal interlinkages can create mismatches, for example, when short-term Fig. 1 Schematic process of climate change adaptation planning. Authors’ design, based on (Kauffman and Hill 2021) 1 3 65 Page 4 of 25 Mitigation and Adaptation Strategies for Global Change (2025) 30:65 interests hinder long-term planning decisions (York et al. 2019). Additionally, urban water systems are often embedded in larger-scale administrative governance systems, where basin-level decisions impact city-level water availability (Daniell and Barreteau 2014; Rivera-Torres and Gerlak 2021). These ‘telecouplings’ (Liu et al. 2013; Miller et al. 2024) significantly complicate effective planning for climate change adaptation but, as we argue, are highly relevant to explore. 3 Materials and methods 3.1 Study site The PMA, located in the Sonoran Desert of Central Arizona, is an urban agglomeration comprising over 20 municipalities, including the four principal cities of Phoenix, Mesa, Scottsdale, and Tempe (Fig. 2). Abundant water availability, driven by an engineered augmentation paradigm and the conversion of highly water-intensive farmland to residential areas, has supported rapid urban expansion in recent decades (Larson et al. 2009; Bolin et al. 2010; Gober et al. 2013; Gilman and Wu 2024). Water availability also allows for vegetation-induced temperature moderation, thereby improving the livability of the desert climate and promoting the sprawl of high-consumption single-family housing, with higherincome areas featuring more green and blue spaces (Larson et al. 2009; Wheeler et al. 2020). Fig. 2 Map of the Colorado River Basin (left) and the Phoenix Metropolitan Area (right), including population, water sources, and demand in acre-feet/year. For data Source, see Table 1 1 3 Page 5 of 25 65 Mitigation and Adaptation Strategies for Global Change (2025) 30:65 Following the state regulation of groundwater (GW) overuse in the 1980s, surface water3 became crucial for municipal water portfolios (Larson et al. 2009, 2013b). In 2022, the total municipal demand amounted to 1.2 million acre-feet (maf) y−1, of which approximately onethird was covered by CAP supplies (ADWR 2023). While water use has been ‘decoupled’ from urban growth since the 1980s, primarily owing to decreasing per-capita use (Richter et al. 2020), current per-capita consumption remains more than twice the national average and has recently increased in most larger municipalities of the PMA ( Table 1, see also Center for the Future of Arizona 2024). The PMA’s water system is highly fragmented, with over a hundred large and small providers operating across the municipalities, and diverse decision-making actors on multiple levels that often create unclear and conflicting goals (Gober et al. 2010; Larson et al. 2013b; Gilman and Wu 2024). Local municipalities and private companies independently regulate water use, pricing, and infrastructure, leading to significant inter-municipal variation (Ouyang et al. 2014). This “uniquely variegated landscape of intra-urban risk to future water scarcity” (Bolin et al. 2010, p. 11) renders the PMA a prime case for geographical research on cross-scalar challenges in urban water sector adaptation. Susceptibility of CAP supplies to future shortages The Central Arizona Project (CAP) is a 336-mile aqueduct system that delivers Arizona’s Colorado River water allocations to users in Central Arizona (Fig. 2 see also Gastélum and Cullom 2013). To secure federal funding in the 1960s, Arizona agreed to hold junior rights in the basin allocation scheme (Hanemann 2002; Kuhn and Fleck 2019). Allocations in the lower basin are unique in that they are tied to the water level in the basin’s largest reservoir, Lake Mead (rather than, as 3 This includes Colorado River water delivered via the Central Arizona Project and water from the Salt and Verde Rivers transported via the Salt River Project (SRP) (Fig. 1). Table1 Population, total demand, proportion of sources in water mix, and demand trend as of 2020 for the 12 largest cities in the PMA City Population Total demand (acre-feet y−1) Water mix Demand trend 20172020iv CAP SRPiEffluentii Groundwateriii Phoenix 1,530.000 379.950 33% 45% 21% 1% Increasing Mesa 505,950 104.190 45% 32% 10% 13% Increasing Gilbert 262,920 65.340 56% 26% 14% 4% Increasing Chandler 262.150 87.620 13% 45% 31% 11% Increasing Scottsdale 232.300 100.230 76% 13% 8% 4% Slightly increasing Glendale 229.990 47.400 45% 45% 6% 4% Stagnant Tempe 174.830 52.940 5% 65% 0 29% Stagnant Peoria 159.620 36.700 54% 25% 19% 2% Increasing Queen Creek 92.130 23.850 2% 0 2% 96% Increasing Avondale 80.080 15.200 0 50% 46% 3% Stagnant Buckeye 58.290 10.470 0 0 92% 8% Increasing Goodyear 54.760 12.890 81% 0 11% 8% Increasing Source: https://www.azwater.gov/ama/ama-data (ADWR 2024). iSRP: Salt River Project, utility provider of surface water from the Salt and Verde Rivers. ii Effluent: treated wastewater. iiiGroundwater withdrawal is state-regulated under the 1980 Groundwater Management Act (Larson et al. 2009). ivDemand trend from 2017–2020, estimated by the authors based on demand curves 1 3 65 Page 6 of 25 Mitigation and Adaptation Strategies for Global Change (2025) 30:65 Brown (2017) rightfully notes, on the ‘health’ of the Colorado River itself). This suggests that municipalities in the PMA are predominantly concerned with developments in reservoir operations and the future water level trajectory in Lake Mead (CAP 2024). In the past decades, the Colorado River streamflow has decreased by approximately 15–20% compared with the average streamflow in the early-20th century, which served as the foundation for basin operations and state allocations (USBR 2012; Lukas and Payton 2020; Kuhn and Fleck 2022). These declines have been linked to prolonged drought, compounded by intensifying climate change impacts on precipitation patterns, evaporation, and the hydrology of mountainous headwaters (Udall & Overpeck 2017; Milly and Dunne 2020; Bass et al. 2023; Schmidt et al. 2023). Concurrently, the Colorado River is heavily exploited, with state allocations exceeding the river’s average streamflow volume (USBR 2012; Richter et al. 2024). Together, these factors have resulted in continuously declining reservoir levels, most notably in Lake Mead (Wheeler et al. 2022; CAP 2024). These trends are expected to persist amid further intensifying climate change. In a hotter and drier future, most hydroclimatic models predict a continuing decline in Colorado River streamflow, with median outcomes ranging from 10 to 20% by mid-century under moderate emission scenarios (USBR 2012; Lukas and Payton 2020; Woodhouse et al. 2021; Whitney et al. 2023). Additionally, anthropogenic and evaporative water demand is expected to increase in a hotter and drier future (Overpeck and Udall 2020; Bass et al. 2023). Despite the CRB’s historically high hydroclimatic variability (Murphy and Ellis 2019; McCabe et al. 2024) and the remaining model uncertainties and wide ranges in model outcomes, it is unlikely that reservoir levels will substantially recover in the long run (Schmidt et al. 2023; Richter et al. 2024). The trend of continuously decreasing water availability in an increasingly arid basin is “[…] robust, highly certain, and well-suited for informing policy choices”, as Udall and Overpeck (2017, p. 2413) note. This not only challenges the entire water governance system in the Southwestern US (Rivera-Torres and Gerlak 2021; Schmidt et al. 2023) but also poses a particular concern for Arizona and municipalities in the PMA. Owing to the state’s junior rights, current contingency measures to stabilize the water level in Lake Mead have predominantly impacted Arizona’s CAP allocations, decreasing supplies by approximately 20% to date (CAP 2024; Arizona Water Blueprint 2024). However, these guidelines will expire in 2026, necessitating a renegotiation process that will determine state allocations for post-2026 Colorado River operations in an increasingly warmer and drier basin (Overpeck and Udall 2020; Gerlak et al. 2021; USBR 2023). It is unclear what agreements the basin states will reach for post-2026 operations and how these will affect Arizona’s CAP supplies and allocations to PMA municipalities. However, coupled with the impacts of climate change on the basin hydrology and the probable increases in internal demand (Dettinger et al. 2015; Wang and Vivoni 2022), this complex hydropolitical and hydroclimatic mélange introduces substantial uncertainties, amplifying the susceptibility of water systems within the PMA both to gradually declining water availability and the risk of short-term supply disruptions (Gastélum and Cullom 2013; Kuhn and Fleck 2019; CAP 2024). This prospect underscores the need to identify, implement, or intensify suitable water management strategies to anticipate, plan for, and adapt to these risks. 1 3 Page 7 of 25 65 Mitigation and Adaptation Strategies for Global Change (2025) 30:65 3.2 Methods We employed a two-stage research design, combining a systematic literature review with semi-structured interviews. The literature review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA, Page et al. 2021). Focusing on peerreviewed, academic literature, we used the SCOPUS database4 and narrowed our search to articles published from 2004–2024. The search was performed in July 2024 and yielded 333 results, out of which 49 articles were included in this study. The inclusion/exclusion criteria for the screening referred to the applicability to the region, the discussion of broader water planning challenges and adaptations in the water sector, and the exploration of one or multiple adaptation measures or strategies (Fig. 3). Semi-structured interviews allowed us to capture planners’ perceptions and identify behavioral choices and challenges in water planning (see also Yin 2009). We conducted interviews with planners in PMA municipalities (n = 7) and experts in regional institutions 4 Search term that has been issued: (TITLE-ABS-KEY (phoenix OR"central arizona"OR maricopa AND urban OR municipal* OR city OR cities OR metropolitan AND water OR hydrolog*) AND PUBYEAR > 2003) AND (LIMIT-TO (DOCTYPE,"ar")) AND (LIMIT-TO (LANGUAGE,"English. Fig. 3 Methodological framework employed in the study design and data analysis, including PRISMA framework flowchart and semi-structured interviews 1 3 65 Page 8 of 25 Mitigation and Adaptation Strategies for Global Change (2025) 30:65 4.2.3 Other strategies Inter-municipal collaboration Current water challenges may provide opportunities for systemic changes in stakeholder networks, promoting more sustainable resource use in the long term (Withycombe-Keeler et al. 2015; White et al. 2019). In the decentralized PMA, this could involve strengthening inter-municipal collaboration and water system planning. At the time of the study, several larger municipalities were members of the Arizona Municipal Water Users Association (AMWUA) which represents municipal interests at the state level. There was broad consensus on the benefits of the AMWUA as a boundary organization, and many interviewees emphasized the need to expand such collaboration (IP1-4, IP8, IP10). Bilateral cooperation, such as creating interconnected pipeline systems or establishing emergency water transfer agreements, was also described as beneficial (IP8, IP10). However, these efforts are often hindered by siloed bureaucratic and socio-political structures (IP2). It remains unclear whether efforts from planners and utilities can drive widespread cooperation, or whether this remains a state-level issue (IP3). The relationship between municipalities and state actors was described as being in need of improvement, with one planner highlighting the political barriers to more effective collaboration (IP10). Decentralized water harvesting Some studies emphasize the potential of decentralized strategies (sometimes referred to as green stormwater infrastructure or low-impact development) such as rainwater harvesting to increase water sustainability (Larson et al. 2013b; Sampson et al. 2016). However, the planners did not discuss this, and the effectiveness of such strategies remains unclear, given the region’s erratic and low precipitation levels (approximately 8 inches (20 cm) annually for Phoenix) (Meerow et al. 2021). Despite the relatively limited amount of stormwater in the region, some cities do have materials or programs to promote green stormwater infrastructure (City of Phoenix 2024). Climate change mitigation With the increasing impact of climate change on water systems in the southwestern US, water planners might be interested in enhancing climate mitigation efforts (Mata and Budhooram 2007; Meerow and Woodruff 2020). For example, Udall and Overpeck (2017) argue that integrated water planning in the CRB must address climate change mitigation to reduce the risk of long-term streamflow decline. In contrast to the literature, our interview findings show that these discussions are not integrated within municipal departments in the PMA, and that water planners are typically not involved in formulating or implementing respective policies or plans, such as climate action plans (IP4, IP7, IP9). 5 Discussion 5.1 Anticipation of new realities in PMA municipalities Our exploration of water planning in PMA municipalities highlights the challenges in translating Climate Change Adaptation Planning (CCAP) into practicable action. The uncertainty planners face regarding future CAP supplies necessitates adaptive planning approaches, and the development of a range of strategies to increase system resilience and reduce municipal vulnerability to potential water shortages. While the diversified water mix has mitigated 1 3 Page 15 of 25 65 Mitigation and Adaptation Strategies for Global Change (2025) 30:65 past drought impacts (thereby supporting theories around system resilience where diversification enhances a system’s ability to absorb disturbances, e.g. Crozier et al. 2024; Kundzewicz et al. 2018), future water shortages remain a pressing concern, and utilities in the PMA are exploring several strategies to address those risks (Table 2). Consistent with the literature on climate change adaptation and water management in urban water sectors (Measham et al. 2011; Hurlimann and Wilson 2018; Vinagre et al. 2023), we find that planned and institutionalized strategies dominate in the PMA. Specifically, our research emphasized the importance of both supplyand demand-side strategies in water adaptation planning, thereby supporting findings in the literature (e.g., Elgendy et al. 2024; Roach et al. 2018; Sawassi and Khadra 2021; Straatsma et al. 2020). However, strategy choices are constrained by the governance context, existing infrastructure, demand patterns, and financial capacities. Our study empirically illustrates how water managers in semi-arid, highly consumptive, and rapidly growing regions operationalize CCAP principles in the face of cross-scalar risks and compound uncertainties. Specifically, it contributes to a deeper understanding of how supply-side options, demand-side constraints, and political trade-offs are prioritized or delayed, depending on local utility capacities, socio-political preferences, and institutional path dependencies. The recovery of water banking credits (through GW pumping) emerged as the first response to acute supply shocks. While these credits promise substantial supply volumes for some utilities, the simultaneous recovery by multiple municipalities could strain aquifers and threaten land stability. This illustrates a potential mismatch between short-term measures and long-term resource sustainability (see also York et al. 2019). Conservation is widely recognized as a crucial strategy but is hindered by socio-political barriers (Boyer et al. 2021). This reflects broader governance challenges in water management (Pahl-Wostl 2006; Hjorth and Madani 2023), where planners must navigate urban development tradeoffs, revenue losses, and public resistance to demand reductions. This might render conservation a purely reactive strategy, thereby delaying effective implementation. Nonetheless, planners emphasized continuous conservation as a reflection of a permanent change in mentality (IP10), fostering a “[…] lifestyle, a way of living in a desert environment that reflects knowledge and understanding of water as a scarce resource” (IP5). This insight extends prior findings (Obringer and White 2024) by showing how conservation is not only a policy mechanism but also a cultural narrative that water utilities in the PMA are beginning to actively shape. Water recycling has emerged as another highly relevant strategy. For PMA municipalities, wastewater might be “[…] one of the most valuable resources for the future” (IP10). This includes both short-term (e.g., non-potable uses, such as outdoor consumption, and water exchanges) and long-term strategies, such as direct potable reuse (DPR), indicating how utilities increasingly view wastewater as a strategy supply source under future scarcity. These findings offer a grounded understanding of how DPR gains traction not only through technological feasibility, but also through shifts in perception among planners (see also Lyle et al. 2023). While the literature on integrated land-water planning (Gober et al. 2011, 2013; Daniell and Barreteau 2014; Gilman and Wu 2024) emphasizes its critical role in addressing urban water stress, our interviews revealed significant institutional and political barriers that limit the extent to which this can be implemented in the PMA. Lastly large-scale desalination remains elusive due to substantial technical and financial barriers. This study thereby empir1 3 65 Page 16 of 25 Mitigation and Adaptation Strategies for Global Change (2025) 30:65 ically confirms the gap between strategic foresight and practical feasibility, which characterizes adaptive water planning under infrastructural and institutional constraints (e.g., Measham et al. 2011; Meerow and Mitchell 2017; Wiechman et al. 2024). 5.2 Toward adaptive planning in the PMA Our findings indicate a growing awareness of the need for long-term planning and the implementation of adaptation strategies among planners at PMA water utilities; however, divergent expectations concerning future CAP supply reliability reflect broader challenges of decision-making under uncertainty, consistent with findings in the literature (Larson et al. 2015; Hui et al. 2018). While some utilities have begun exploring such approaches, others remain anchored to traditional planning frameworks, underscoring the region's gradual and uneven adoption of climate change adaptation principles and strategies. Planners face significant challenges in preparing for long-term resilience, particularly when they take into account worst-case model uncertainties which become greater the further planners look into the future. Our contribution here lies in revealing how uncertainty is not only a modeling issue but also a governance barrier that shapes the discretionary scope of planners and risk communication within utilities. While easily implementable strategies, such as unobtrusive conservation goals and indoor retrofits, are already employed, future water shortages will likely pose more complex questions and decisions, e.g., enacting mandatory demand reductions. The reluctance among planners to interfere with residential preferences and urban development patterns highlights a fundamental tension between the region’s growth-oriented economic paradigm and the need for more adaptive management to safeguard long-term water sustainability. Unsurprisingly, one planner noted that “[…] addressing growth through water planning is not a pleasant conversation in Arizona” (IP5). This tension echoes findings in earlier work on water sustainability in the PMA, such as by Larson et al. (2009, 2013b), Bolin et al. (2010), or Gober et al. (2010). This, we argue, reaffirms that climate adaptation is not merely about technical strategy adoption, but also requires renegotiation of political and development trajectories (Meerow and Mitchell 2017; Macpherson et al. 2024). It remains to be seen whether PMA municipalities will directly or indirectly favor engineered solutions that might risk infrastructural lockins, and whether current planning principles will enable utilities to develop the flexibility, responsiveness, and anticipatory capacity required to address complex future uncertainties. More transformational adaptation strategies may involve fundamental changes to economic paradigms, development patterns, and institutional structures to achieve sustainable and equitable water systems in the PMA (e.g., Pahl-Wostl 2015; Shi and Moser 2021). This perspective aligns with broader observations that water scarcity often results from governance failure rather than from resource limitations, thus involving political power dynamics and allocation practices (Meerow and Mitchell 2017; Pincetl et al. 2019; Macpherson et al. 2024). As we have demonstrated for the PMA, such governance dynamics are reflected in everyday planning dilemmas and hesitations, especially concerning urban growth management and demand restrictions. In addition to these internal dynamics, our study highlights the scalar dependencies faced by water planners in the PMA, which aligns with findings in the literature (e.g., Adger et al. 2005; Straatsma et al. 2020; Miller et al. 2024). CAP supplies are highly 1 3 Page 17 of 25 65 Mitigation and Adaptation Strategies for Global Change (2025) 30:65 susceptible not only to reductions due to increasing climate-induced water stress, but also to Arizona’s junior priority in the Colorado River allocation scheme and the uncertainty surrounding post-2026 basin operations. As such, as one planner noted, “[…] one of the biggest uncertainties is how the state and how the regions respond to these Colorado River shortages” (IP4). These findings make a timely contribution by situating municipal planning efforts within the upcoming post-2026 Colorado River negotiations. Our results suggest that local utilities must anticipate localized climate impacts and plan in relation to uncertain and evolving distant hydroclimatic developments, cross-scalar risks, and institutional decision-making. In this way, this study offers policy-relevant insights that can support regional planners and intergovernmental actors in the PMA, as well as other arid regions worldwide facing future water supply uncertainties, to better plan for, design, and implement adaptive strategies that account for cross-scalar dependencies and path-dependent susceptibilities. 5.3 Study limitations and further research However, the study’s results require cautious interpretation due to several limitations. The limited number of interviews and the purposive sampling approach constrain the generalizability of the findings and may not fully represent the full diversity of stakeholders concerned with the planning and implementation of adaptive responses in the water management of the PMA. Specifically, we did not engage every municipality or multiple representatives from utilities, potentially limiting the range of planning perceptions. The focus on larger municipalities may also overlook challenges and adaptive responses specific to smaller municipalities. Moreover, the analysis excluded master plans, state policies, and broader institutional documents, as well as external influences such as federal policies and interstate water negotiations, all of which could reveal additional adaptation strategies and shape local water management. Finally, while we aimed to discuss challenges and barriers to adaptation strategies comprehensively, we could not delve deeply into technical enablers or barriers that could significantly affect the success of strategies. Despite these limitations, this research contributes valuable exploratory insights and opens multiple avenues for further inquiry. Our qualitative research approach offers a rich, contextual understanding (Seamon and Gill 2016; Lim 2024) of how planners navigate the institutional, technical, and behavioral complexities of urban adaptation planning. Future research should integrate larger, more diverse participant pools and adopt more extensive mixed-method designs that may combine qualitative depth with quantitative sampling, probabilistic designs, and statistical cluster analysis to strengthen empirical robustness and generalizability. An integrated analysis of planning documents and institutional processes, as conceptualized by Kauffmann and Hill (2021), could also enhance the understanding of how adaptive strategies are developed, implemented, and socially learned over time. In light of increasing water scarcity and climate risks in the southwestern US (Overpeck and Udall 2020; Kuhn and Fleck 2022), understanding the complex, multi-scalar nature of urban water adaptation remains critical research priority. Future research should emphasize comprehensive methodological frameworks capable of capturing the socio-political, ecological, and technical dimensions of adaptation within large and interconnected human– environment systems. 1 3 65 Page 18 of 25 Mitigation and Adaptation Strategies for Global Change (2025) 30:65 6 Conclusions The outlook of a hotter and drier future in the southwestern US, coupled with Arizona’s junior priority for Colorado River supplies and the uncertainties around post-2026 river operations, poses increasing risks for future Colorado River water supply reliability for PMA municipalities. These complex hydroclimatic and hydropolitical uncertainties require water utilities to explore and implement adaptation strategies to mitigate potential CAP supply shortages and ensure long-term water system reliability and sustainability. In this study, we weave together the results of a literature review and interviews with PMA water planners to explore adaptation strategies in the face of these challenges. By bridging adaptation research and urban studies, we contribute to a growing understanding of how localized water adaptation planning is shaped by its broader institutional, infrastructural, and socio-political context. Our findings show that while many municipalities in the PMA are not yet directly impacted by supply cuts and benefit from diversified portfolios, planners anticipate heightened future water stress and recognize the need to invest in both alternative supply and demand-side strategies. A range of strategies, differing in relevance, intent, timing, and scope, are being considered to varying degrees by municipalities and planners in their water utilities. However, perspectives on long-term risk and appropriate responses vary across municipalities, reflecting different levels of institutional preparedness, political support, and resource capacity. The recovery of water banking credits emerged as a prominent short-term response to potential supply shocks. In the mediumto long-term, demand reductions through enhanced conservation efforts and increased use of treated wastewater, either for nonpotable purposes or via DPR, are seen as essential. However, implementing these strategies presents considerable challenges, including technical limitations, ecological constraints, and socio-political sensitivities. Our findings demonstrate reluctance among planners to implement actions that impact residential lifestyles, such as mandatory demand reductions, underscoring how water planning is constrained by the region’s long-standing growthoriented, neoliberal socio-political system (see also Bolin et al. 2010). Moreover, we highlight how localized water planning and adaptation efforts are deeply embedded in and constrained by larger-scale hydrological and administrative dynamics. CAP supplies, which link the PMA to the CRB, depend on a complex interplay of hydroclimatic conditions, basin demand, and operational guidelines. Uncertainties regarding future availability are compounded by the unknown outcomes of the Reconsultation process, which introduces further ambiguity for Arizona’s CAP supplies. In this context, some planners express a preference for working with conservative CAP expectations, rather than relying on uncertain, politically negotiated outcomes – which was described by one interviewee as an annual “shot in the dark” (IP5). Ensuring resilient water systems amidst these uncertainties remains a critical priority in the PMA. While Arizona’s legal and institutional water governance frameworks seem to slowly adapt to the realities of the 21st century, many of the prevailing responses remain incremental and reactive. Long-term planning may be challenging for a relatively young region. Nevertheless, its historical experience in managing resource variability and uncertainty may also allow the municipalities to address future challenges effectively. While the strategies discussed in this study may contribute to improving the resilience of municipal water systems in the PMA in light of an uncertain future supply of Colorado 1 3 Page 19 of 25 65 Mitigation and Adaptation Strategies for Global Change (2025) 30:65 River water, there is a need to question whether the prevailing incremental and reactive approaches, particularly regarding demand options, are sufficient to address the profound challenges ahead or whether more transformative changes are required (see also Gober et al. 2010; Larson et al. 2015; Shi and Moser 2021). Future research should investigate how these strategies are implemented, their contributions for long-term water system resilience, and monitor the implications of the Reconsultation negotiations for Arizona’s water planning. Acknowledgements This work was supported by a student stipend from the German Academic Exchange Service. We are grateful for Dr. Robert Kitzmann's contribution to the study. We thank the participating PMA water planners and regional experts for their insights and time. Lastly, we thank Lindsay Lohr, Maike Schlebusch, and Maximilian Möller for their valuable comments and editorial advice. Author’s contribution Paul Schulze: Conceptualization, Data curation, Formal analysis, Methodology, Visualization, Writing – original draft, Writing – review and editing. Sara Meerow: Conceptualization, Validation, Writing – review and editing. Funding Open Access funding enabled and organized by Projekt DEAL. Data availability The data (transcripts) that support the findings of this study are available from the corresponding author upon request. Declarations Research involving human participants This research involved human participants. Informed consent Informed consent has been given by all participants. The study design has been approved by the Institutional Review Board of the Office of Research Integrity and Assurance at the Arizona State University. Competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. 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