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Article

Estimated Impacts of Future Environmental Conditions on Water Quality in the Chesapeake Bay Beyond Midcentury

by
Lewis C. Linker
1,*,
Gopal Bhatt
2,
Richard Tian
3 and
Raymond Najjar
4
1
Chesapeake Bay Program Office, U.S. EPA, Annapolis, MD 21401, USA
2
Chesapeake Bay Program Office, The Pennsylvania State University, Annapolis, MD 21401, USA
3
Chesapeake Bay Program Office, UM Center for Environmental Science, Annapolis, MD 21401, USA
4
Department of Meteorology and Atmospheric Science, The Pennsylvania State University, University Park, PA 16802, USA
*
Author to whom correspondence should be addressed.
Climate 2026, 14(3), 66; https://doi.org/10.3390/cli14030066
Submission received: 21 January 2026 / Revised: 28 February 2026 / Accepted: 3 March 2026 / Published: 9 March 2026
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Abstract

In order to set nutrient and sediment load targets for the Chesapeake Bay, projections of changing environmental conditions through 2055 have been previously considered. This article expands the analysis through 2085. Under future ensemble scenarios of General Circulation Models (GCMs), temperature and precipitation trends for the Chesapeake Bay watershed prior to midcentury have a rate of change more than twice that of the post-midcentury trend. Prior to midcentury, runoff and nutrient loading to the Bay estuary are projected to increase. In this analysis, model simulations for post-midcentury suggest the trend of increasing runoff may be reduced. The combined effect of a reduced trend in temperature and precipitation increases post-midcentury with continued sea level rise in the ensemble scenarios leads to a decreasing trend in Chesapeake hypoxia post-midcentury, resulting in a leveling off of dissolved oxygen water quality degradation.

1. Introduction

Located on the U.S. mid-Atlantic coast, the Chesapeake Bay has the largest surface area of any estuary in the contiguous United States (Figure 1), and like many East and Gulf coast estuaries, it is impacted by elevated nutrient loading and hypoxia [1,2]. In 2010, the Chesapeake Bay Program (CBP), a federal and state partnership, developed the Chesapeake Total Maximum Daily Load (TMDL), which is a eutrophication management plan to improve water quality and habitat [3,4]. The science behind the 2010 TMDL is documented in eleven articles in a Journal of the American Water Research Federation (JAWRA) Featured Collection and in USEPA [3,5].
Changing environmental conditions were documented in the 2010 TMDL as an influence on Chesapeake Bay water quality, but were excluded from consideration at the time because of insufficient information to quantify their impact [3,6]. Since establishing the TMDL, extensive research has been carried out to estimate the impact of changing environmental conditions on temperature and precipitation [7,8,9,10], tidal wetland erosion [11,12], sea level rise [13,14,15,16] and other factors affecting Chesapeake pollutant loads [17].
A previous assessment of changing environmental condition impacts on the Chesapeake Bay and its watershed was done as part of the Midpoint Assessment in 2020 to set additional nutrient and sediment reductions required to maintain water quality standards under 2025 environmental conditions. The previous pre-midcentury assessment used four decadal periods centered on 2025, 2035, 2045, and 2055, conditions that are three, four, five and six decades, respectively, beyond the end year of the 1993–1995 critical period, and the 1991–2000 base hydrology and nutrient loads used to set the 2010 Chesapeake TMDL allocations [4]. The assessment was based on CBP decision-making approaches, with the model findings providing the basis for additional nutrient and sediment reductions applied to achieve living resource-based TMDL water quality standards under 2025 environmental conditions.
Key drivers were considered, including changes in precipitation volume and intensity, evapotranspiration, atmospheric carbon dioxide (CO2) concentration, streamflow, and nutrient and sediment loads [10,18]. The impacts of other environmental drivers, including water-column warming, sea level rise, tidal wetland loss, and phenological changes in nutrient loading were also examined [11,12,15,16,19,20]. Model simulations using integrated watershed, airshed, and estuarine models suggest that, by midcentury, changing environmental conditions are likely to increase streamflow and nutrient loads to the Bay [10,21,22,23]. In the Bay, warming will reduce dissolved oxygen solubility and increase respiration and stratification [13,15], exacerbating hypoxia. These results indicate that increasing nutrient reductions will be needed to maintain habitat-based water quality standards of dissolved oxygen (DO). Overall, the study from 1995 to midcentury (2055) showed that increasing temperatures, flows, and loads, along with a complex interaction with sea level rise, influenced the Bay’s restoration goals by requiring increased nutrient reductions to maintain DO water quality standards. A detailed discussion of these findings is documented in thirteen articles in a JAWRA Featured Collection [24].
The relationship between higher temperatures, increased precipitation, and higher nutrient loadings to coastal waters is also seen in the Baltic Sea. In the Baltic, watershed nutrient loads are influenced by precipitation volumes, with periods of elevated precipitation coinciding with increased nutrient loads [25]. Increases in hypoxic conditions since the mid-20th century have been linked to nutrient loading and climate-driven changes [26]. Future climate projections in the Baltic estimate increased precipitation in northern subbasins, producing higher nutrient loads along with increases in bottom hypoxic volumes [27].
Understanding near-term changes prior to midcentury is critical for informing strategies to meet Bay restoration goals. In the longer term, however, a related goal of Chesapeake Bay Program modeling and planning is to anticipate major changes and prevent surprises. A data and information gap in what to anticipate beyond midcentury with respect to the Chesapeake DO water quality standards exists. Therefore, a long-term post-midcentury look into the changing environmental conditions of the Chesapeake Bay and its watershed is warranted.
The objective of this paper is to examine the long-term trajectory of estimated nutrient reductions required to achieve and maintain living-resource-based DO water quality standards in the Chesapeake Bay. This objective is achieved through the use of sensitivity scenarios examining the major influences of temperature, precipitation, and sea level rise using the Chesapeake watershed and estuarine models. Sensitivity scenarios for 2065, 2075, and 2085 were developed to examine the influence of key forcing functions on Chesapeake Bay nutrient and sediment loads and on subsequent Bay water quality beyond midcentury.
Explicit in the paper’s objective is the examination of how post-2050 climate trends affect hypoxia and, in particular, how varying rates over time of sea level rise, warming, and increased precipitation volumes and loading influence hypoxia in the Chesapeake Bay.
Extending the study beyond midcentury provides results suggesting a leveling of water quality hypoxia degradation post-2050 due mainly to the leveling of increases in temperature and precipitation, which tend to increase hypoxia, and to continued increases in sea level rise, which reduce hypoxia due to increased gravitational circulation.

2. Materials and Methods

The CBP’s Phase 6 suite of airshed, watershed, land use, and tidal water quality models has undergone six major phases of development and application since the introduction of the first watershed and tidal Bay models in 1987. They are extensively reviewed and documented, and the Phase 5 suite of models was used to establish the historic 2010 Chesapeake TMDL [4,17,28,29,30,31,32]. The Phase 6 suite of models is the most recent version and was finalized in 2017 [33]. The Phase 6 model suite specifically includes a model of the airshed (the Community Multiscale Air Quality Model or CMAQ), a watershed model (Phase 6 Chesapeake Bay Watershed Model), a land-use model (Chesapeake Bay Land Change Model or CBLCM), and a tidal Bay water-quality model (2017 Chesapeake Bay Water Quality and Sediment Transport Model or WQSTM). The Phase 6 suite of models is used as a linked system, with the output of the airshed and land use model being used as the input to the watershed model, and the airshed and watershed model outputs being used as input to the estuarine model.
The Phase 6 Watershed Model’s response to future environmental conditions of increased precipitation volumes is through its sensitivity to increased surface and subsurface flows and subsequent greater nutrient loads. In addition, greater simulated runoff volumes and intensity under future environmental conditions generate greater scour and loads of sediment and particulate nutrients from rivers and reservoirs.
In this article, the CBP Phase 6 airshed, land use, watershed, and tidal water quality models were used to predict changes in water quality conditions in the Chesapeake brought about by future environmental conditions of 2065, 2075, and 2085. Previously, the years 1995, 2025, 2035, 2045, and 2055 were examined [10,17]. We used an ensemble of scenarios of the Intergovernmental Panel on Climate Change (IPCC) 5th Assessment Report (AR5) in both our previous analysis (1995 to 2055; [10]) and in this current (2065 to 2085) analysis of changing environmental condition impacts to Chesapeake Bay water quality. Specifically, the ensemble average of statistically downscaled Coupled Model Intercomparison Project Phase 5 (CMIP5) Representative Concentration Pathways (RCP) 4.5 scenarios of “modest mitigation” and the higher emissions RCP 8.5 using Bias-Correction Spatial Disaggregation, BCSD method [34,35], were applied as inputs to the integrated Phase 6 watershed, airshed, and estuarine models [17].
All Phase 6 watershed model future environmental condition scenarios were run using the delta method [36,37,38]. The delta method adjusted precipitation volumes and intensities to represent future environmental conditions of higher watershed flows and loads in future years and was used as input to the 2017 Chesapeake Bay WQSTM. The WQSTM was then used to evaluate the response of Bay water quality standards of Deep Water DO (set at 3 mg/L) and Deep Channel DO (set at 1 mg/L) [3,12,15,38].

3. Results

3.1. Watershed Impacts from Future Environmental Conditions Beyond Midcentury

Prior to midcentury, estimated changes in watershed inputs to the Bay from 1995 (the Chesapeake TMDL Reference Period, [3,4]) to 2025 show increases in streamflow and loads of nitrogen, phosphorus, and sediment of 2.4, 2.6, 4.5, and 3.8%, respectively (Figure 2a; Table 1). During this period, increases in precipitation volume (3.1%) and intensity were estimated based on an analysis of long-term monitoring data. Post-midcentury simulations for 2085 environmental conditions of RCP 4.5 (Figure 2b) show estimated precipitation, flow, and nitrogen, phosphorus, and sediment load increases relative to the 1995 Reference Period of 8.4, 8.0, 17.0, 45.2, and 28.2%, respectively. Temperature, precipitation, flow, and loads of nutrients and sediment are estimated for all decadal RCP 4.5 and RCP 8.5 scenarios from 2025 to 2085 in Table 1.
In Table 1, for RCP 4.5 and RCP 8.5, the ensemble median of 31 statistically downscaled General Circulation Models (GCMs) was used. The hybrid method indicates a combination of observed precipitation trends, and model ensemble medians were used as described in [10]. The hybrid approach provides another line of evidence of future increases in precipitation volumes and intensity, particularly for short-range future predictions, by using the 88-year trend in observed precipitation at a county scale (approximately 500 km2) combined with GCM ensemble precipitation estimates [10].
The 2025 to 2055 results were previously described [17]. The 1995 Reference Period was used to set a standard base for the percent change in flow and loads for all future scenarios from 2025 to 2085. The 1995 Reference Period had an average estimated annual precipitation of 105.6 cm, streamflow of 44.8 cm, nitrogen load of 90.3 million kg, phosphorus load of 6.09 million kg, and sediment load of 8.43 billion kg.
The 1995 Reference Period applied the simulated point source and nonpoint source load management of the Watershed Implementation Plan Phase 3 (WIP3) that the CBP partnership agreed to implement to achieve water quality standards under the Chesapeake TMDL. The same management practices of the 1995 Reference Period were then modified by the changing future environmental conditions of 2025 to 2085 as shown in Table 1 and summarized in Figure 2.
The estimated flow, nutrient, and sediment load increases due to changing environmental conditions over the next 75 years will present challenges for the CBP management of Chesapeake Bay water quality, but the post-midcentury rate of increase diminishes after midcentury for the modest carbon emission mitigation RCP 4.5 scenario. (Figure 3a). On the other hand, temperature under the high emissions RCP 8.5 scenario continues to increase at an unabated rate.
In Figure 3, the prior assessment of changing environmental conditions for the years 2025, 2035, 2045, and 2055 was based on RCP 4.5 for air temperature, whereas the change in precipitation was based on long-term observed trends for 2025, RCP 4.5 for 2055, and a blend of the long-term observed trend and RCP 4.5 for 2035 and 2045 [10]. This analysis for 2065, 2075, and 2085 considers the ensemble median of both RCP 4.5 and RCP 8.5.
The amelioration of warming under the modest mitigation RCP 4.5 scenario has consequences for the Chesapeake Bay as it controls moisture in the air, which in turn governs the volume and intensity of precipitation and ultimately the delivery of freshwater, nutrient, and sediment loads from the watershed to the estuary [10]. Figure 3a shows the decreased rate of temperature increase of 0.16 °C decade−1 post-midcentury in the RCP 4.5 scenario compared to 0.31 °C decade−1 pre-midcentury. The reduced rate of post-midcentury temperature increase coincides with the reduced rate of precipitation increase under the RCP 4.5 scenario. Figure 3b shows a similar difference in pre- and post-midcentury rates of precipitation change. Interestingly, despite the unabated increases in temperature of the no mitigation RCP 8.5 scenario (Figure 3a), the estimated precipitation increases seem to be limited to about 10 percent relative to the 1995 Reference Period (Figure 3b) for unknown reasons.
The relative rate of change in both temperature and precipitation for the 31 individual GCMs in the ensemble providing environmental change inputs to the seven 2025 to 2085 CBP scenarios can be seen in Appendix Figure A1. For the RCP 8.5 scenario, 14 out of 31 individual GCMs had a similar temperature vs. precipitation response as indicated in Figure 3. In the case of the RCP 4.5 scenarios, the pattern was less distinct, likely due to the more limited range of projected change in temperatures of the RCP 4.5 scenarios as compared to that of the RCP 8.5, as seen in the two temperature change boxplots in Appendix Figure A1. For each of the ensemble’s 31 statistically downscaled GCMs, using the BCSD method, the RCP 4.5 and RCP 8.5 decadal scenarios were examined for trends in precipitation and temperature change for pre-midcentury (2025–2055) and post-midcentury (2065–2085). The distributions of pre- and post-midcentury linear trends of individual GCMs (first two boxplots in Figure A1) show a lower rate of change (or increase) of precipitation post-midcentury as compared to that of pre-midcentury in both RCP 4.5 and RCP 8.5. Similar distributions for air temperature (last two boxplots in Figure A1) show a lower rate of change (or increase) in post-midcentury air temperature as compared to that of pre-midcentury in RCP 4.5 but a higher rate of change in RCP 8.5. Interestingly, the interquartile range for the post-midcentury trend is smaller in both RCP 4.5 and RCP 8.5 for both air temperature as well as precipitation, except for RCP 8.5 precipitation.
A decadal analysis of Multivariate Adaptive Constructed Analogs (MACA) [39] based statistical downscaling of 20 GCMs from the CMIP5 shows similar pre- and post-midcentury relative rate of change in air temperature and precipitation as described above, but with a substantially lower rate of change in precipitation post-midcentury under RCP 8.5 (Appendix Figure A2).

3.2. Tidal Bay Impacts from Future Environmental Conditions Beyond Midcentury

Major effects of changing environmental conditions on the Chesapeake Bay are (1) water-column warming, generating more hypoxia because of decreased dissolved oxygen solubility, increased deep-water respiration, and increased stratification; and (2) higher nutrient and sediment loads delivered to the Bay from the watershed (Figure 4). As a counterbalance, increased estuarine circulation brought about by sea level rise decreases hypoxia [15].
Under the estimated 2025 Phase 3 Watershed Implementation Plan (WIP3) loads and conditions, a 1.06 °C temperature increase, as shown in Figure 2, increases average summer (June–September) hypoxic volume (DO < 1 mg/L) through decreased solubility of oxygen (48%), increased respiration (43%), and increased stratification (9%) (Figure 4—blue stacked bar for 2025 RCP 4.5). However, the estimated reduction in the rate of temperature increases after midcentury under the RCP 4.5 scenario will moderate these effects on deep water hypoxia. Of note in Figure 4 is that the individual physical conditions of Warmer Waters bars and Sea Level Rise bars both had a greater influence on hypoxia than the increased loading from the watershed and airshed (Watershed Loads).
However, sea level rise is expected to continue at rates shown in Figure 2 and Appendix Figure A3 to 2150 and likely beyond, reducing hypoxia through increased gravitational circulation in the Bay, lower bottom water temperatures, and other effects [13,14,15,16], as shown in Figure 4. Increased gravitational circulation, due to a more open Bay mouth cross section, allows greater coastal ocean exchange with the Bay, providing greater bottom water inflow from the ocean as well as a greater surface outflow, with the overall effect of increased ventilation of Chesapeake hypoxic bottom waters. In addition, increased gravitational circulation lowers bottom water temperatures, which also reduces bottom water hypoxia.
A countervailing influence of sea level rise on reduced hypoxia would be the loss of tidal wetland nutrient attenuation, assuming that tidal wetlands are unable to migrate landward. However, tidal wetland loss has a relatively minor influence on hypoxia compared to increased gravitational circulation [12,15].
Figure 4 shows that sea level rise reduces hypoxia in the Chesapeake to a considerable extent, more than enough to counter the increased nutrient loads from 2025 or 2085 environmental change, but with only half the impact of water temperature increase in the estuary and its attendant increase in hypoxia due to reduced DO solubility, increased respiration, and increased stratification.

3.3. Overall Influence of Increased Temperature, Flow, Watershed Loads, and Sea Level on Hypoxia

Hypoxia under the RCP 4.5 scenario is estimated to increase from 2025 to 2085, but its rate of increase is decreasing over time and becoming asymptotic without further hypoxia increases between 2075 and 2085 (Figure 5). Then, hypoxia decreases in a scoping scenario of 2135 sea level rise, keeping temperature and loads at 2085 levels. Under these conditions, estimated Chesapeake hypoxia approaches 2025 conditions.
However, there are several layers of contributing factors to consider (Figure 5). The estimated effect of increased RCP 4.5 estuarine water-column temperature (green dashed line with triangle markers) is the most dominant component of environmental change contributing to increasing Chesapeake Bay hypoxia, and its trend of monotonic increase stops at 2065 (rate of increase post-midcentury is 51% less than that of pre-midcentury). Loads from the watershed (green dashed line with cross markers) follow a similar pattern but have a slower rate of increase from 2055 (rate of increase post-midcentury is 30% less as compared to pre-midcentury) due to the magnitude and spatial variability of precipitation, temperature, and flows. The positive effect of the sea level rise trend in reducing hypoxia is estimated (green dashed line with plus sign markers, where the rate of hypoxia post-midcentury is 17% less as compared to pre-midcentury).
In contrast to the RCP 4.5 scenario, the RCP 8.5 ensemble of scenarios (shown for the 2055 to 2085 period) continues a monotonic trend of increased hypoxia to 2085 (purple solid line), driven primarily by continued temperature increases (purple dashed line with triangle markers). The estimated sea level rise component of RCP 8.5 hypoxia (purple dashed line with plus sign markers) is similar to the RCP 4.5 scenario trend.

4. Discussion

Projected post-midcentury changes in environmental conditions and associated impacts on the Chesapeake Bay will be increasingly determined by trends in the trajectory of global fossil fuel emissions. Recent growth in low-CO2-emission energy sources coupled with renewable energy sources becoming less expensive and GHG mitigation policies are all estimated to contribute to the trend of CO2 emissions leveling off with a long plateau projected for midcentury and decreases in the later quarter of the century [40,41], which is consistent with the scenario results presented here. The overall trend could have some long-term positive influence, or at least less negative influence, on Chesapeake Bay water quality, particularly for the overall combined estimated environmental change impacts, including sea level rise, on the habitat-based DO water quality standard.
After midcentury, the influence of GHG emissions tracked in the modest mitigation RCP 4.5 and no mitigation RCP 8.5 scenarios will become more important as they diverge. Thus, impacts on the Bay will vary depending on worldwide mitigation response and management. The Chesapeake Bay Program has initiated an analysis of what’s required to maintain the Chesapeake TMDL and restoration goals under 2035 environmental conditions and beyond, making GHG mitigation management relevant to ecosystem management in eutrophic estuaries.
The International Energy Agency (IEA) estimates of current global CO2 emissions show climate mitigation policies tracking slightly higher and proposed mitigation policies slightly lower than the RCP 4.5 scenario [42]. The RCP 4.5 scenario is equivalent to the newer SSP2 (Shared Socioeconomic Pathway 2) modest mitigation scenario of the latest CMIP6 scenarios. Both are plausible and consistent with current observed GHG emissions, and both estimate a 2.5 °C increase in global temperature by 2100. This is compared to the RCP 8.5 scenario, which is tracking higher than currently observed CO2 emission estimates [40] (Figure 6), though this scenario better captures cumulative CO2 emissions, which are a better predictor of changing environmental conditions [43]. Superimposed on the global GHG emissions from Huasfather and Peters [40] in Figure 6 are estimated regional responses of total Chesapeake Bay hypoxia volume (DO < 1.0 mg/L) for RCP 4.5 scenarios from 1995 to 2130, which follow the same pattern with a lag time as the global GHG emissions.

Long Tails and Uncertainties in the Chesapeake Climate Future

In the Bay estuary, sea level rise has been shown to counteract the negative impacts of increased watershed and airshed loads on DO. After midcentury, a period that is highly uncertain, temperature and precipitation increases may level off under modest mitigation RCP 4.5 conditions, but SLR is expected to continue unabated. In the long term, post-2100, these changes may help offset climate-induced hypoxia impacts experienced prior to midcentury.
Our analysis provides a quantitative linkage of climate and GHG mitigation to Chesapeake Bay water quality. The CBP is already actively engaged in adaptation to future environmental conditions in the Bay and its watershed. For example, sea level rise is estimated to continue unabated to 2150 and beyond, and adaptation to this trend is crucial for low-lying resources of the Chesapeake Bay (e.g., submerged vegetation, tidal marshes, coastal forests, and developed infrastructure). Likewise, increased precipitation, flooding, and the likelihood of extreme events are motivating watershed adaptation in stormwater and flood management.
While the need for further steep nutrient and sediment reductions beyond midcentury to achieve the habitat-based living resource DO water quality standards in the Chesapeake Bay could be less likely, adaptation will be an ongoing challenge. Insights into where decision-makers need to consider placing their adaptation efforts to minimize climate risk are important.
Changing environmental conditions are a multi-generational challenge for Chesapeake Bay restoration. While impacts of environmental change on Chesapeake Bay water quality are inevitable over the century, there is some evidence that by midcentury, the rates of increased temperature, precipitation, nutrient loads, and hypoxia could begin to decrease.
In the Chesapeake Bay watershed, major projected environmental change influences are greater precipitation volumes and intensities, which increase flows and consequently delivery of nitrogen, phosphorus, and sediment loads to the Bay [10,17]. In the Chesapeake, the estimated key impacts on water quality standards are higher water-column temperatures, which decrease dissolved oxygen solubility and increase stratification, and deep-water respiration, both of which increase hypoxia [15]. However, sea level rise and freshwater inflows (in the absence of their associated higher nutrient loads) from the watershed are estimated to increase estuarine circulation and ameliorate somewhat the estimated increase in hypoxia.
With the continued increase in sea level beyond 2100, the combined influence of these factors is likely to lessen the need for nutrient reductions post-midcentury to maintain DO water quality standards suitable for living resources. Maintaining a low-CO2-emission mitigation path is important for Chesapeake Bay water quality and has implications for other eutrophic coastal waters of the East and Gulf coasts of the United States. The Chesapeake and other eutrophic estuaries could see similar continuing water quality degradation until about midcentury, followed by a leveling off of degrading water quality conditions toward the end of the century and improving hypoxia conditions beyond the close of the century due to increasing sea level rise and relatively constant precipitation and loads under modest (RCP 4.5) GHG mitigation strategies.
There are limitations in this study that point to future research. The results discussed in this paper are conditional on the methods, models, and scenarios used in this study. A first-order action to reduce uncertainty in this analysis will be to redo the analysis with the latest CMIP6 scenarios and the new suite of CBP Phase 7 Chesapeake Bay models now being developed, which have improved spatial and temporal resolution as well as other refinements. In addition, the outcomes of individual GCMs as shown in Figure A1, rather than an ensemble approach, could be explored given time and resources.

Author Contributions

L.C.L. provided authorship; conceptualization; data curation; formal analysis; investigation; methodology; project administration; resources; supervision; validation; writing—original draft; writing—review and editing. G.B. provided authorship; conceptualization; data curation; formal analysis; investigation; methodology; software; validation; and writing—review and editing. R.T. contributed authorship; conceptualization; data curation; formal analysis; investigation; methodology; software; validation; and writing—review and editing. R.N. provided authorship; conceptualization; and writing—review and editing. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

Data are available upon request from the corresponding author.

Acknowledgments

The authors thank the CBP’s Modeling Workgroup and Scientific and Technical Advisory Committee (STAC) for their ongoing review and guidance of the development, application, and analysis of climate using the CBP models of the watershed, airshed, and estuary. We also thank Thomas Johnson (U.S. Environmental Protection Agency, Office of Research and Development) for his valuable review provided on this research. We also thank Maria Herrmann (Penn State) for facilitating an analysis based on the MACA downscaling method.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
U.S.United States
EPAEnvironmental Protection Agency
UMUniversity of Maryland
CMIP5Coupled Model Intercomparison Project Phase 5
CMIP6Coupled Model Intercomparison Project Phase 6
RCPRepresentative Concentration Pathway
TMDLTotal Maximum Daily Load
CBPChesapeake Bay Program
CBPOChesapeake Bay Program Office
JAWRAJournal of American Water Resources Association
DODissolved Oxygen
CMAQCommunity Multiscale Air Quality Model
CBLCMChesapeake Bay Land Change Model
WQSTMWater Quality Sediment Transport Model
IPCCIntergovernmental Panel on Climate Change
BCSDBias-Correction Spatial Disaggregation
GCMGeneral Circulation Model
PT-LOEPlanning Target Level of Effort
PRCPrecipitation
TASSurface Air Temperature
TNTotal Nitrogen
TPTotal Phosphorus
SSSuspended Sediment
PSUPractical Salinity Unit
CCelsius
CH3D-ICMChesapeake Bay Estuarine Model (CH3D hydrodynamic and ICM water quality code)
GHGGreenhouse Gas
MACAMultivariate Adaptive Constructed Analogs
WIPWatershed Implementation Plan
WIP3Phase 3 Watershed Implementation Plan
IEAInternational Energy Agency
SSPShared Socioeconomic Pathway
CO2Carbon Dioxide
SLRSea Level Rise

Appendix A

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Figure A1. The change in precipitation vs. the change in air temperature relative to the 1995 Reference Period for CMIP5 RCP 4.5 (green circles) and RCP 8.5 (purple circles) ensembles for the years 2025, 2035, 2045, and 2055 [10] and for 2065, 2075, and 2085 (this analysis). Box plots show distribution of linear trend fitted to four decades, before and after midcentury for precipitation and temperature for both RCP 4.5 and RCP 8.5.
Figure A1. The change in precipitation vs. the change in air temperature relative to the 1995 Reference Period for CMIP5 RCP 4.5 (green circles) and RCP 8.5 (purple circles) ensembles for the years 2025, 2035, 2045, and 2055 [10] and for 2065, 2075, and 2085 (this analysis). Box plots show distribution of linear trend fitted to four decades, before and after midcentury for precipitation and temperature for both RCP 4.5 and RCP 8.5.
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Figure A2. Change in precipitation and air temperature over the Chesapeake Bay Watershed based on the MACA (Multivariate Adaptive Constructed Analogs) downscaling product from The Climatology Lab of John Abatzoglou. The MACA method [39] was applied to the output of 20 GCMs from the fifth phase of the Coupled Model Intercomparison Project (CMIP5) run under historical radiative forcing until 2005 and then for the RCP 4.5 and 8.5 scenarios until 2100. Shown are median changes in 30-year averages centered on 2025, 2035, 2045, 2055, 2065, 2075, and 2085 as compared to 1995.
Figure A2. Change in precipitation and air temperature over the Chesapeake Bay Watershed based on the MACA (Multivariate Adaptive Constructed Analogs) downscaling product from The Climatology Lab of John Abatzoglou. The MACA method [39] was applied to the output of 20 GCMs from the fifth phase of the Coupled Model Intercomparison Project (CMIP5) run under historical radiative forcing until 2005 and then for the RCP 4.5 and 8.5 scenarios until 2100. Shown are median changes in 30-year averages centered on 2025, 2035, 2045, 2055, 2065, 2075, and 2085 as compared to 1995.
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Figure A3. Estimated median sea level rise projections at Baltimore under emissions scenarios included in the IPCC AR6. Source: Boesch et al. [44] 2023; NASA Sea Level Projection Tool and Sea-Level Rise Projections for Maryland.
Figure A3. Estimated median sea level rise projections at Baltimore under emissions scenarios included in the IPCC AR6. Source: Boesch et al. [44] 2023; NASA Sea Level Projection Tool and Sea-Level Rise Projections for Maryland.
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Figure 1. The Chesapeake watershed and Bay, showing the states of New York, Pennsylvania, Maryland, Delaware, Virginia, West Virginia and the District of Columbia of the Chesapeake Bay Program (CBP) Federal–State partnership. Green colors represent the lower elevations of the Coastal Plain and Piedmont physiographic regions and tan colors represent the higher elevations of the Appalachian Highlands and mountains of the Ridge and Valley physiographic regions.
Figure 1. The Chesapeake watershed and Bay, showing the states of New York, Pennsylvania, Maryland, Delaware, Virginia, West Virginia and the District of Columbia of the Chesapeake Bay Program (CBP) Federal–State partnership. Green colors represent the lower elevations of the Coastal Plain and Piedmont physiographic regions and tan colors represent the higher elevations of the Appalachian Highlands and mountains of the Ridge and Valley physiographic regions.
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Figure 2. Effects of 2025 (a) and 2085 (b) estimated changes in environmental conditions on the Chesapeake Bay and its watershed relative to the 1995 Chesapeake TMDL Reference Period.
Figure 2. Effects of 2025 (a) and 2085 (b) estimated changes in environmental conditions on the Chesapeake Bay and its watershed relative to the 1995 Chesapeake TMDL Reference Period.
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Figure 3. Change in air temperature (a) and precipitation (b) relative to 1995 for the ensemble median of 31 statistically downscaled CMIP5 RCP 4.5 and RCP 8.5 scenarios.
Figure 3. Change in air temperature (a) and precipitation (b) relative to 1995 for the ensemble median of 31 statistically downscaled CMIP5 RCP 4.5 and RCP 8.5 scenarios.
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Figure 4. Estimated hypoxia effects under 2025 Phase 3 WIP conditions (Blue bars) and 2085 Phase 3 WIP conditions (Red bars)—without environmental change effects (Reference); with the addition of environmental change watershed and airshed loads (Watershed Loads); with the addition of 2025 sea level rise (Sea Level Rise); with the addition of 2025 water-column warming (Warmer Water; D: Contribution of DO solubility to the total increase in hypoxia volume from the Reference scenario; R: Contribution of respiration to the total hypoxia volume increase; S: Contribution of stratification to the total increase in hypoxia volume increase); and with all three factors combined (All Together). Hypoxia volume (in km3) is the average in the summer (June–September) from 1991 through 2000 in the whole Bay with DO concentration lower than 1 mg/L.
Figure 4. Estimated hypoxia effects under 2025 Phase 3 WIP conditions (Blue bars) and 2085 Phase 3 WIP conditions (Red bars)—without environmental change effects (Reference); with the addition of environmental change watershed and airshed loads (Watershed Loads); with the addition of 2025 sea level rise (Sea Level Rise); with the addition of 2025 water-column warming (Warmer Water; D: Contribution of DO solubility to the total increase in hypoxia volume from the Reference scenario; R: Contribution of respiration to the total hypoxia volume increase; S: Contribution of stratification to the total increase in hypoxia volume increase); and with all three factors combined (All Together). Hypoxia volume (in km3) is the average in the summer (June–September) from 1991 through 2000 in the whole Bay with DO concentration lower than 1 mg/L.
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Figure 5. Estimated Chesapeake hypoxia (June to September DO < 1.0 mg/L) for the decadal increments of environmental conditions from 2025 to 2085 all with the Phase 3 Chesapeake Watershed Implementation Plan (WIP3) under RCP 4.5 (green lines) and RCP 8.5 (purple lines). The hypoxia volume in the 1990s is for estimated watershed loads and the Bay under the WIP3 conditions at the 1991–2000 base hydrology condition. Dashed lines with + markers are sea level rise, with × markers are nutrient load increase, and with triangle markers are temperature increase. Solid lines are the combined effect of sea level rise, nutrient load and temperature increases. The 2130 scenario kept all inputs the same as 2085 RCP 4.5 but the sea level rise changed to the 2130 level.
Figure 5. Estimated Chesapeake hypoxia (June to September DO < 1.0 mg/L) for the decadal increments of environmental conditions from 2025 to 2085 all with the Phase 3 Chesapeake Watershed Implementation Plan (WIP3) under RCP 4.5 (green lines) and RCP 8.5 (purple lines). The hypoxia volume in the 1990s is for estimated watershed loads and the Bay under the WIP3 conditions at the 1991–2000 base hydrology condition. Dashed lines with + markers are sea level rise, with × markers are nutrient load increase, and with triangle markers are temperature increase. Solid lines are the combined effect of sea level rise, nutrient load and temperature increases. The 2130 scenario kept all inputs the same as 2085 RCP 4.5 but the sea level rise changed to the 2130 level.
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Figure 6. Global annual CO2 emission estimates (adapted from [40]) and estimated regional responses of total Chesapeake Bay hypoxia (June to September DO < 1.0 mg/L).
Figure 6. Global annual CO2 emission estimates (adapted from [40]) and estimated regional responses of total Chesapeake Bay hypoxia (June to September DO < 1.0 mg/L).
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Table 1. Watershed-wide estimated average change in annual precipitation (PRC), surface air temperature (TAS), streamflow (Flow), and loads of nitrogen (TN Load), phosphorus (TP Load), and suspended sediment (SS Load) delivered to the Chesapeake Bay for 2025 to 2085 with respect to the 1995 Reference Period.
Table 1. Watershed-wide estimated average change in annual precipitation (PRC), surface air temperature (TAS), streamflow (Flow), and loads of nitrogen (TN Load), phosphorus (TP Load), and suspended sediment (SS Load) delivered to the Chesapeake Bay for 2025 to 2085 with respect to the 1995 Reference Period.
CLIMATEMETHODLAND USE∆PRCPRC∆TAS∆FLOWFLOW∆TN LOADTN LOAD∆TP LOADTP LOAD∆SS LOADSS LOAD
(%)(cm)(°C)(%)(cm)(%)(106 kg)(%)(106 kg)(%)(109 kg)
2025Trend20253.1%108.91.122.4%45.82.7%92.74.3%6.353.8%8.75
2035Hybrid20254.2%110.11.463.7%46.44.7%94.59.1%6.648.4%9.14
2035Hybrid20354.2%110.11.463.9%46.55.0%94.89.7%6.688.7%9.17
2045Hybrid20255.2%111.11.814.5%46.86.5%96.114.9%6.9912.4%9.49
2045Hybrid20455.2%111.11.814.8%46.97.1%96.616.7%7.1013.3%9.55
2055RCP4.520256.4%112.42.056.2%47.510.4%99.724.0%7.5518.4%9.99
2055RCP4.520556.4%112.42.056.7%47.811.8%100.927.4%7.7620.0%10.12
2065RCP4.520556.4%112.42.276.2%47.510.6%99.926.0%7.6817.7%9.92
2075RCP4.520557.4%113.42.427.6%48.216.3%105.043.7%8.7526.9%10.70
2085RCP4.520558.0%114.02.538.4%48.517.0%105.645.2%8.8428.2%10.81
2055RCP8.520557.9%114.02.937.5%48.117.3%105.942.1%8.6529.4%10.91
2065RCP8.520559.0%115.13.578.3%48.521.2%109.456.5%9.5336.7%11.53
2075RCP8.520559.7%115.94.218.4%48.523.4%111.463.2%9.9439.7%11.78
2085RCP8.5205510.1%116.34.778.9%48.826.6%114.372.4%10.5044.7%12.20
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Linker, L.C.; Bhatt, G.; Tian, R.; Najjar, R. Estimated Impacts of Future Environmental Conditions on Water Quality in the Chesapeake Bay Beyond Midcentury. Climate 2026, 14, 66. https://doi.org/10.3390/cli14030066

AMA Style

Linker LC, Bhatt G, Tian R, Najjar R. Estimated Impacts of Future Environmental Conditions on Water Quality in the Chesapeake Bay Beyond Midcentury. Climate. 2026; 14(3):66. https://doi.org/10.3390/cli14030066

Chicago/Turabian Style

Linker, Lewis C., Gopal Bhatt, Richard Tian, and Raymond Najjar. 2026. "Estimated Impacts of Future Environmental Conditions on Water Quality in the Chesapeake Bay Beyond Midcentury" Climate 14, no. 3: 66. https://doi.org/10.3390/cli14030066

APA Style

Linker, L. C., Bhatt, G., Tian, R., & Najjar, R. (2026). Estimated Impacts of Future Environmental Conditions on Water Quality in the Chesapeake Bay Beyond Midcentury. Climate, 14(3), 66. https://doi.org/10.3390/cli14030066

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