From assessment to action: informing water resource management in protected areas amid global change

Abstract

Water resources are vital to the United States National Wildlife Refuge System, the world’s largest network of lands managed solely for the conservation of fish, wildlife, and habitats. Despite their protected status, these areas remain vulnerable to global change impacts. A standardized Water Resource Inventory and Assessment database was used to examine climate-related water threats across the refuge system. Over half of all units identified at least one climate related threat, with insufficient surface water most frequently reported—particularly at sites where threat severity was ranked high. Other common issues included altered flow regimes, habitat loss or change, excess surface water, compromised infrastructure, and degraded water quality (e.g., elevated salinity or chlorides). This system-wide baseline provides a foundation for tracking shifts in hydrologic threats over time. These findings can inform conservation policy, guide resource allocation, and support strategic water management to sustain ecological integrity across the refuge system.

1 Introduction

The National Wildlife Refuge System (NWRS) is the largest network of public lands and waters (~346 million hectares) conserved specifically for fish, wildlife, and their habitats (Meretsky et al., 2006). NWRS units can be found throughout North America, from the Caribbean to Alaska, providing a continental scale system of conservation areas for fish and wildlife including many at risk species. The system consists of 573 National Wildlife Refuges (NWRs), 38 Wetland Management Districts, and five Marine National Monuments, which are managed under the purview of the United States Fish and Wildlife Service (USFWS). These protected areas support high levels of biodiversity and ecological integrity (Clark and Slusher, 2000; Fischman and Adamcik, 2011; Noss, 2004). Ecosystem services originating from these lands, such as freshwater supply and regulation, were previously estimated to be worth $26.9 billion per year (Ingraham and Foster, 2008) in 2008 when the NWRS encompassed 60 million hectares (Griffith et al., 2009), a value that has likely increased as more acreage has been added. Unlike other protected areas centered on geologic features (e.g., Yellowstone National Park), NWRS units were established to conserve habitat for specific fish and wildlife groups, including migratory birds, marine mammals, threatened and endangered species, and game animals. Over the past century, the focus on migratory bird conservation, especially waterfowl, has led to a strong overrepresentation of aquatic habitats such as marshes, seasonal wetlands, riparian corridors, and prairie potholes within the system. However, these freshwater habitat types are underrepresented in other protected land networks in North America (e.g., National Parks) making the refuge system a vital yet overlooked component of conservation efforts for freshwater aquatic species (Scott et al., 2004).

Freshwater habitats often have an outsized influence on wildlife species occurrence, even when they do not occupy the largest areas geographically. For example, riparian areas account for 5% of the land cover but provide crucial habitat for 50% of bird species that occupy NWRS units along the lower Colorado River watershed (Taylor, 2017). Likewise, freshwater ecosystems in protected areas often serve as guardians of biodiversity since these areas may provide the only remaining habitat for threatened or endangered species plus globally, freshwater habitats have the highest animal species richness per area (Román-Palacios et al., 2022). Freshwater biodiversity is declining more rapidly than terrestrial or marine ecosystems (Dudgeon, 2019), and remains highly vulnerable to widespread threats such as emerging contaminants (Reid et al., 2019) and agriculture (Osgood, 2017). Freshwater ecosystems rank among the most imperiled globally (Collen et al., 2009) and pressures are expected to increase as human population densities rise near freshwater resources (Vörösmarty et al., 2013). These ecosystems are extremely important for local human communities as they provide recreational opportunities and food resources, including fish, shellfish, and other aquatic organisms, and contribute to water purification, flood regulation, and storm protection (Lynch et al., 2023). Patterns in freshwater biodiversity can signal environmental stress on aquatic ecosystems, affecting their services, and ultimately human wellbeing (Portela, 2025).

Water is a vital component of the NWRS, with management efforts heavily focused on water resources. Staff on NWRS units devote considerable time to activities such as monitoring water conditions, surveying aquatic species, and manipulating water levels to support wildlife habitat and food availability. Freshwater is also a limited resource, however, and competition for its allocation continues to intensify with climate change and the expanding human footprint. Recent research highlights that unsustainable freshwater use poses significant challenges for human societies, which are likely to escalate with global change (Haddeland et al., 2014; Kåresdotter et al., 2025; Wake, 2021).

Given the increasing competition for freshwater, one of the central challenges for the NWRS is to ensure that sufficient quantities of high quality water are available for fish, wildlife, and their habitats. Effective water resource management requires robust data collection and interpretation; thus, a system-wide inventory is essential to identify threats, prioritize actions, and support informed decision-making. In response, the Water Resources Inventory and Assessment (WRIA) Project (Bauch et al., 2021) was initiated over a decade ago to implement a standardized, comprehensive inventory and assessment of water resources across the NWRS. This standardized framework facilitates consistency in data collection and terminology (e.g., insufficient water means the same thing everywhere), enabling comparative analyses and coordinated management strategies across spatial scales.

Each WRIA compiles existing baseline information—such as geospatial data on water rights, quantity, quality, management practices, and threats (including climate change impacts)—into a centralized database with integrated GIS and web-based tools that can be queried. The assessment component involves expert evaluation of this data by hydrologists and other specialists to identify site-specific water resource issues and develop science-based recommendations. These outputs support management action at multiple spatial scales (e.g., for a single unit or a group of units in the same eco-region) and inform regional and national planning and prioritization efforts.

The NWRS and other networks of protected areas play a critical role in supporting ecosystem and species adaptation to global change processes, including climate change, sea level rise, and land use shifts (Johnson et al., 2015; Lehikoinen et al., 2021). Climate change is already altering the water resources upon which the NWRS depends to fulfill its mission (Caruso et al., 2025). Units are increasingly experiencing climate-related impacts such as flooding and storm surges that damage wetland infrastructure, prolonged droughts that create competition for limited water supplies, and sea-level rise that threatens to permanently transform coastal habitats (Newman, 2024). In response, the NWRS has initiated numerous efforts to enhance ecological resilience. These include implementing Nature-Based Solutions (NBS) to reduce flood impacts (Opperman and Galloway, 2022), developing drought contingency plans, acquiring land to offset coastal marsh loss, and applying the Resist-Accept-Direct (RAD) framework for adaptation planning (Moorman et al., 2025). Despite these efforts, questions remain: What are the most prevalent climate-driven threats across the NWRS? Are there patterns or shared challenges among units experiencing these impacts? A consistent, system-wide assessment specific to climate change impacts is needed to quantify effects, identify common needs, and inform targeted, scalable adaptation strategies across the NWRS. Such an assessment is vital not only for measuring progress but also for addressing persistent gaps and barriers to effective adaptation.

The WRIA database was utilized to examine the effects of climate change on water resources across the NWRS. Statistical summaries of the most common and severe climate-related threats and drivers were generated, and their geographic distribution and spatial patterns of occurrence were assessed. Specifically, we examined (1) the most frequently reported and severe climate-related water threats, and (2) how these threats vary across regions and landscapes. This study represents the first nation-wide assessment of climate change impacts on water resources throughout a network of protected areas set aside for fish and wildlife conservation, providing a foundational understanding of emerging vulnerabilities. By identifying spatial patterns of threats, these results can inform management decisions related to water infrastructure planning and maintenance, habitat restoration, and climate adaptation planning across NWRS units. Our analysis also highlights critical knowledge gaps, which can guide future monitoring and data collection efforts to strengthen water resource management under changing climatic conditions.

2 Methods

2.1 Data acquisition

This assessment used 11 years of data (2011–2022) from the WRIA National Database, representing 471 NWRS units (National Wildlife Refuges and Wetland Management Districts), which represents 77% of the 611 units in the NWRS. The database is administered by NWRS headquarters, with data entry conducted by eight regions using flexible approaches, which included staff interviews, detailed reports, and area-wide surveys. Most regions used a standardized Excel spreadsheet developed to batch-load multiple threats into the database.

The dataset represents a single, consolidated record of threat information rather than a temporal sequence. Although entries span 11 years, most were added during a coordinated update in 2018, with additional updates made at the discretion of regional representatives. Multiple information sources informed entries in the WRIA database, all of which were quality-assured to ensure consistency and reflect the most current status at the time of entry.

2.2 Data classification

An important component of the WRIA National Database was the ability to capture data related to threats and needs associated with water resources. To enable querying and analysis, the user team recognized the necessity of establishing a classification system to organize threats and needs. Subsequently, a standardized set of lists for threats and needs was developed, providing a consistent selection for all users. Threats were classified into threat types (e.g., threats) and causes (e.g., drivers). After several iterations, the user team identified a list of 32 threat types organized in three broad categories: Water Quality, Water Quantity, and Aquatic Habitat. Threat causes were more varied, the user team identified 89 potential causes organized into six categories: Water Quality, Water Supply/Quantity, Water Management Capability, Water Rights/Legal, Landscape Alteration, and Climate. These categories were primarily for organizational purposes, as any threat type could be associated with any cause. A threat type could have multiple causes, but each relationship was considered a separate threat in the WRIA National Database. This approach was taken because each cause may require a different solution, or mitigating one cause might not eliminate the threat if other causes persist.

Threat classifications were further identified and filtered where the threat was caused by a climate factor. Threats with climate factors indicated a vulnerability to climate drivers, and it was assumed that this vulnerability would continue with ongoing climate change. It was also assumed that if a threat occurred because of a climate factor, then the threat is one that has been persistently observed over time (e.g., extreme precipitation events) or projected to occur more frequently in the future (e.g., change in frequency of extreme precipitation events).

In addition to threat type and cause, attributes required for each threat included severity, time frame, data source, data quality, and agency ability to address the threat. Of relevance to this assessment was threat severity and categories were defined as follows:

• High: Prevents fulfillment of unit purpose(s) or NWRS mission; threatens public safety; threatens Threatened and Endangered (T&E) species; threatens adverse legal consequences; threatens infrastructure

• Moderate: Hinders completion of one or more management objectives (e.g., degrades habitat for non T&E species; inadequate infrastructure for habitat management)

• Low: Directly or indirectly affects unit operations but does not hinder unit purpose(s) or management objectives

• Unknown: Insufficient information to determine severity

Indicators provided the underlying observations for threat classifications, but in our analysis, threat type and severity were treated as pre-assigned categorical outcomes. We assessed whether severity patterns varied by type or climate attribution, rather than modeling severity from the raw indicators.

2.3 Data analyses

Data were analyzed using R Statistical Software (version 4.3.3; R Core Team 2024). Data entered into the WRIA National Database as of July 25th 2022 were extracted and an R-script was developed to summarize key metrics using these data. The computational workflow included filtering for climate-related threats, summarizing unique refuge-threat combinations, and tabulating frequencies of threats and drivers nationally and by region. The R-script included code to perform the filtering required to identify climate related threats and drivers (hereafter, climate threats and climate drivers). The code also incorporated a quality control mechanism, where records of poor or questionable quality were filtered out (e.g., fields assessing data quality and source were left blank). This filtering process ensured that only records with verified quality and known sources were retained for analysis.

To identify the most common climate threats and climate drivers, the frequency of unique combinations of refuge and threat type where the threat has a climate influenced cause were tabulated. The most common climate related threat occurrences where the severity was rated as high were also tabulated, to consider which threats may pose the greatest challenge to mission fulfillment throughout the NWRS. Results were summarized in bar graphs according to the top 10 most common threats and the top five most common high severity threats. To statistically assess the severity of climate-related threats, we used chi-squared tests of independence to determine whether severity rankings (high, moderate, low) were distributed differently across (1) climate-related threat types, and (2) climate-related versus non-climate threats overall. We calculated Cramer’s V to report effect size (magnitude). Understanding climate drivers is imperative for pinpointing effective climate adaptation strategies and evaluating their feasibility. Therefore, climate drivers were also examined in a similar manner by summarizing the top 10 most common drivers and the top five most common high severity drivers in bar graphs.

To examine if there were differences in climate threats and climate drivers across the nation and between regions, geographic patterns of occurrence for the top 5 most common threats and drivers were qualitatively evaluated. ArcGIS Pro software was used to assess data based on its geographic location and maps were created to illustrate spatial patterns and relationships. Maps displayed NWRS unit locations where at least one occurrence of a particular climate related threat or driver was recorded. Color coding was used to indicate the severity ranking of each threat or driver (high, moderate, low). Using generated maps, a qualitative analysis was performed to identify and interpret patterns in the regional breakdown of common climate threats and climate drivers across the country. Unique threats or drivers only found in one region and not others were also identified.

2.4 Data limitations

The WRIA National Database represents the best available information related to water resources across the NWRS. There were differences in data collection efforts and interpretation, however, which reflect variability among the eight regions and subjectivity among individuals entering data within the same region. For example, a region that followed initial database guidelines to conduct area-wide surveys of multiple NWRS units would likely uncover fewer threats than a region that assessed each unit more intensively, such as from completion of a detailed database report. Similarly, regions that utilized a variety of data entry processes were more likely to lump or split entries. To increase consistency and minimize bias, counts of the number of unique threat occurrences at each NWRS unit were included, rather than the total number of threats. To account for differences in data interpretation, the database provided definitions to guide assignment of attributes (e.g., threat severity, information quality) with a certain amount of latitude for professional judgment. Results from periodic questionnaires sent to regional staff indicated that threat codes were primarily made by a hydrology expert (45%), or strictly followed the database definitions (27%), or both (19%).

3 Results

Out of the 471 NWRS units accounted for in the WRIA National Database at the time of analysis, more than half documented at least one climate-related threat (Figure 1). Among the types of climate-related threats (hereafter, climate threats), insufficient surface water was the most common overall and most often cited where the severity was ranked as high (Figure 2). Other climate threats included in the top 10 most common were altered flow regimes, loss or alteration of a habitat type, excess surface water, insufficient ground water, compromised water management, altered thermal regime, and water quality metrics (e.g., increased salinity or chlorides; Figure 2a). Insufficient surface water, habitat shifting/alteration, and loss/alteration of wetland habitat were not only among the most common climate threats but were also among the top 5 most common threats where severity was ranked as high (Figure 2b). The top five most severe also included compromised water management capability and loss/alteration of estuarine habitat, but these climate threats were not as common overall (Figure 2b). Altered flow regimes and excess surface water were among the most cited climate threats but were not often identified as being severe, indicating that these threats may be widespread, but their impact is not as strong or unknown.

Figure 1

Figure 2

Among the causes of climate-related threats, climate warming, drought, extreme precipitation, and sea level rise were the most often cited causes (hereafter, climate drivers) and were also commonly cited as high severity (Figure 3a). Other climate drivers included in the top 10 most common were changes in precipitation patterns, rain-snow regime, storm induced coastal erosion, storms, temperature extremes, glacial retreat, and changes in wildfire frequency/severity. The top five most severe also included rain-snow regime, although this driver was cited less overall in comparison to other high severity drivers (Figure 3b).

Figure 3

For the chi-squared tests of independence within climate-related threats, severity differed significantly by threat type (χ² = 87.6, df = 38; simulated p ≈ 1 × 10⁻⁴) with a moderate association strength (Cramer’s V = 0.268). When comparing climate-related to non-climate threats overall, the severity distributions also differed significantly (χ² = 21.0, df = 2, p = 2.7 × 10⁻⁵), with climate-related threats showing relatively more high and fewer low ratings than expected, and this association was small (Cramer’s V = 0.086).

Geographic patterns of occurrence were exhibited for the top five most common climate threats (Figure 4A). Insufficient surface water was frequently reported by NWRS units in the western and southern regions of the nation. Altered flow regimes was evenly distributed throughout the lower 48 states and Alaska. Habitat shifting/alteration was primarily clustered in Alaska and the southern or western regions of the nation, while excess surface water was more common in the eastern half of the country. Loss or alteration of wetland habitat was less commonly cited overall and principally clustered along the east coast (Figure 4A).

Figure 4

Spatial distribution of the top five most common climate drivers was similar to patterns observed for climate threats (Figure 4B). Both climate warming and drought were frequently cited as drivers by NWRS units evenly distributed throughout the nation, although drought was cited more often. Extreme precipitation appeared to be a larger issues predominately east of the Mississippi River. Sea level rise was cited as a climate driver among coastal NWRS units in every region including Alaska and Hawaii. Change in precipitation patterns (non-extreme) was commonly reported by the interior portions of the nation, such as the Midwest or Great Plains region (Figure 4B).

In terms of assessing relationships among top climate threats and drivers (Supplementary Table 1), insufficient surface water was most frequently linked to drought. Other drivers commonly associated with insufficient surface water were climate warming, rain-snow regime change, changes in precipitation patterns (non-extreme) and glacier retreat. The most common driver of altered flow regimes was climate warming, followed by extreme precipitation, changes in precipitation patterns (non-extreme), drought, and rain-snow regime change. A shift or alteration in habitat was primarily linked to climate warming, followed by sea level rise, change in precipitation patterns (non-extreme), drought, and tropical storm or hurricane. Extreme precipitation was the most common driver of excess surface water; other drivers included a change in precipitation patterns (non-extreme), climate warming, rain-snow regime change, and sea level rise. Climate warming and sea level rise were equally reported as drivers for the loss or alteration of wetland habitat, followed by sea level rise, drought, extreme precipitation, and storm induced coastal erosion (Supplementary Table 1). Although climate warming was the most frequently cited driver overall, this category often lacked specificity in the database, which suggested that the underlying causes of this driver may be unknown or multi-faceted.

4 Discussion

This study provides the first nation-wide assessment of climate-related threats to water resources across the NWRS, revealing a widespread and uneven pattern of vulnerabilities that are already influencing the ecological and operational landscape of protected areas in the United States. More than half of the assessed NWRS units identified climate change as a threat, underscoring the magnitude of emerging global change factors on the ecological integrity and management of the refuge system. These findings build on earlier modeling studies. For instance, Magness et al. (2011) assessed the climate vulnerability of 501 NWRS units based on exposure, sensitivity, and adaptive capacity, classifying approximately half of the units as moderately (n = 161) or highly vulnerable (n = 76), with the remainder considered low vulnerability (n = 264). A more recent study examined climate analogs for 48 NWRS units in California and Nevada under four future climate scenarios. Of the five analog categories, 10–25 units were projected to face disappearing climates, 8–16 to have unique climates shared with only one other unit, 3 to have widely occurring climate conditions, 3 to retain enduring climates, and 4 to serve as climate hubs—with larger units occurring in up to three categories (Choe et al., 2020).

The analysis revealed that insufficient surface water, altered flow regimes, and habitat shifts were the most widespread water related climate threats affecting the NWRS. These results align with findings from previous studies focused on individual NWRS units (Caruso et al., 2025; Griffith et al., 2009; Moss et al., 2024), reinforcing that climate-driven water scarcity and habitat transformation are already manifesting throughout the nation, especially in western and southern regions. For example, coastal marsh habitats within NWRS units located in the South Atlantic region are undergoing substantial ecological changes (Moorman et al., 2024). As sea levels rise, these coastal marshes are migrating, with projections indicating that two-thirds of this migration will replace freshwater habitats, and one-third will displace upland areas (Osland et al., 2022). Likewise, coastal marshes in Texas are failing to keep pace with accelerating sea level rise, placing both the wetlands and the critical ecosystem services they provide at increasing risk (Moon et al., 2022).

Insufficient surface water was the most frequently and severely cited climate threat, reflecting a clear pattern of escalating water scarcity across much of the western and southern United States. This finding is consistent with broader hydrological trends, including intensifying droughts, long-term aridification, and increased evapotranspiration linked to warming temperatures (Condon et al., 2020; Ficklin et al., 2022; Overpeck and Udall, 2020; Sardans et al., 2024). The strong association between this threat and drought, warming, and changes in precipitation regimes highlights a convergence of stressors that are expected to intensify with future climate change (McElwee et al., 2023; Payton et al., 2023). Altered flow regimes and habitat shifts—especially in Alaska, the West, and coastal areas—further demonstrate that climate-driven hydrologic and ecological transformations are not isolated to a single region but are system-wide in nature.

These findings have important implications for water resource management and adaptation planning. Many NWRS units were established to conserve hydrologically dependent species and now support a disproportionately high concentration of aquatic habitats and species vulnerable to climate change (Czech, 2005; Fischman et al., 2014; Griffith et al., 2009; Johnson et al., 2015). This vulnerability is projected to intensify in arid regions, where groundwater extraction and surface water diversions reduce available water on the landscape, resulting in many species becoming restricted to protected areas. For instance, federally endangered spring snail species are restricted to springs habitat at Bitter Lake National Wildlife Refuge in New Mexico, while endangered Sonoran Pronghorn (Antilocapra americana sonoriensis) depend on managed water infrastructure within wildlife refuges in Arizona. The frequency and severity of water related threats underscore the need for more proactive and spatially differentiated management strategies. In regions where surface water is becoming increasingly scarce, increased collaboration with neighboring water users to share and optimize water resources, along with infrastructure modifications for improved water retention (Micklin, 2007) and the use of nature based solutions such as wetland restoration (Narayan et al., 2017), could enhance water availability and ecosystem resilience. In coastal areas, where sea level rise is a top driver of habitat loss, strategies such as marsh migration corridors (Kirwan and Megonigal, 2013), sediment augmentation (Thorne et al., 2018), or the application of the Resist-Accept-Direct framework (Lynch et al., 2022; Thompson et al., 2021) may be necessary to maintain habitat function.

This analysis also reinforces the importance of standardized assessments like WRIA. By providing specific definitions, spatially explicit data, and expert evaluations across hundreds of units, WRIA enables comparative analysis that would otherwise be very difficult across such a large and diverse network. This is particularly important for identifying shared threats, facilitating cross-unit learning, and prioritizing regionally coordinated adaptation efforts (Cross et al., 2012; Magness et al., 2022). As global change impacts to water resources become more complex and interdependent, such data infrastructure becomes essential for aligning local management actions with national conservation objectives (Beger et al., 2015; Lawler et al., 2015).

Moving forward, this baseline analysis can serve as a foundation for temporal tracking of global change impacts across the NWRS, enabling systematic evaluation of adaptation progress. Incorporating WRIA data into scenario planning tools (Nicholson et al., 2019) and decision frameworks (Open-File Report, 2025), climate resilient design protocols (Xiao et al., 2023), and landscape connectivity analyses (Belote et al., 2016) could help align local adaptation actions with broader ecosystem management goals. Future efforts that link WRIA results with remote sensing, national biodiversity and ecosystem services datasets, or Indigenous knowledge systems would enhance predictive capacity and broaden the assessment’s relevance (Shultz et al., 2022). Moreover, similar efforts could be extended to other protected area networks, such as state wildlife areas and international reserves. Doing so would support more comprehensive assessments of water resource vulnerability at national and global scales and promote coordinated adaptation strategies across boundaries (Gleick, 2003; Lehner et al., 2011; Watson et al., 2018).

5 Conclusion

The NWRS faces persistent and evolving challenges to mission success, many of which are rooted in water availability, quality, and infrastructure. The WRIA project represents the most comprehensive effort to date to provide refuge managers and agency leadership with consistent, actionable data to guide resource allocation, monitoring, and adaptation efforts. Our results establish a valuable national-scale baseline to assess long-term trends and track shifts in threat patterns driven by climate change and infrastructure developed to respond. Several strategies may support broader application of WRIA findings to strengthen climate resilience across the NWRS. These include expanding the use of water monitoring data to inform adaptive responses to climate-related threats, facilitating cross-regional collaboration on climate change vulnerability assessments, and improving data collection to evaluate the effectiveness of water management and adaptation strategies. Notably, climate change vulnerability assessments continuously emerge as one of the greatest needs among managers in the NWRS, highlighting the degree to which climate concerns are embedded in broader water resource challenges. Strengthening watershed partnerships, modernizing infrastructure, and integrating hydrological modeling or remote sensing tools can help translate qualitative assessments into more mechanistic, predictive frameworks. Finally, linking WRIA outputs with national datasets on biodiversity, ecosystem services, and Indigenous knowledge systems could enhance decision-making and deepen our understanding of climate risk. Although our study focuses on the United States, the approach and indicators presented are broadly applicable across diverse climatic zones, hydrologic regimes, and land-use contexts, and can be adapted to other regions worldwide with appropriate local calibration and validation. Similar assessments can be expanded to other protected area networks globally to support broader-scale planning, prioritization, and investment in climate-resilient water management.

As climate change continues to reshape water availability and distribution, understanding and addressing related threats to freshwater ecosystems in conservation lands is critical. The patterns we identify here provide a blueprint for prioritizing climate adaptation and ensuring that the NWRS continues to serve as a cornerstone of biodiversity conservation and climate resilience in the United States.

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