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2025 Washington Metropolitan Area Drought Exercise

Authors: S. Ahmed, H. Moltz, S. Nummer, C. Schultz, and A. Seck | Pub: # ICP26-1 | Published in April 2026

The 2025 Washington Metropolitan Area (WMA) Drought Exercise Report documents the planning, execution, and outcomes of a two-day regional drought coordination exercise, with a pre-exercise kickoff meeting held in advance, led by the Section for Cooperative Water Supply Operations on the Potomac (CO-OP) of the Interstate Commission on the Potomac River Basin (ICPRB). The purpose of this report is to summarize the scenarios, decisions, operational lessons, and recommendations developed during the exercise, which brought together the Washington metropolitan area’s major water suppliers and CO-OP staff to practice coordinated drought response.

This exercise serves as an annual opportunity for CO-OP staff and utility personnel to strengthen their understanding of Drought Operations, evaluate communication protocols, and rehearse the technical and decision-making processes used when Potomac River flows decline. By simulating severe, historically based drought conditions modified for future system configurations, the exercise helps ensure that the Drought Operations team maintains operational readiness and a shared understanding of roles, tools, and responsibilities. The report provides a record of these activities and highlights areas for continued improvement in forecasting, coordination, and information sharing across the region.

From Planning to Action: Advancing Sustainable Water Resources Management in the Potomac Basin

Authors: Heidi L. N. Moltz | Pub: # PRC26-1_Moltz | Published in February 2026

The Potomac River basin, a critical source of drinking water and home to the U.S. capital, provides a case study in sustainable water resources management. This paper traces the history of planning in the basin, examines the opportunities and challenges of water resources management in a complex, multi-jurisdictional setting, and analyzes the integrated, adaptive process used to develop and implement the Potomac Basin Comprehensive Water Resources Plan. Using a review of planning documents and stakeholder engagement outcomes, the analysis identifies key mechanisms through which adaptive, collaborative planning is operationalized across four analytic dimensions: stakeholder engagement, facilitation, plan components, and planning process. The Potomac case demonstrates how integrative principles can be implemented pragmatically through voluntary, science-based, and locally grounded collaboration—rather than applying Integrated Water Resources Management (IWRM) as a formal or prescriptive framework. The findings highlight how institutional capacity, iterative learning, and cross-jurisdictional coordination enable basin-scale planning to evolve over time. Unlike previous Potomac scientific and planning reports, this paper offers a systematic, reflective analysis of the long-term planning process in the Potomac basin, providing empirically grounded insights and a conceptual framework for others pursuing integrated, sustainable water resources management.

This article was published in the Journal of the American Water Resources Association on February 18, 2026 (Volume 62, Issue 1). DOI: https://doi.org/10.1111/1752-1688.70097

Limnofasciculus delicatus (Coleofasciculaceae, Coleofasciculales), a Novel Mat-Forming Cyanobacterium From Shenandoah River, Virginia, USA

Authors: Rosalina Stancheva, Cecilio Valadez-Cano, Benoit Van Aken, Gordon M. Selckmann, Janice Lawrence, A. Bruce Cahoon | Pub: # PRC26-4 | Published in June 2026

Benthic cyanobacterial mats in flowing waters are complex communities typically composed of taxa from the orders Coleofasciculales and Oscillatoriales, many of which have unresolved taxonomic positions and poorly characterized toxic potential. We collected field mats of a benthic non-heterocytous filamentous cyanobacterium from the North and South Forks of the Shenandoah River in Northern Virginia (USA) that were dominated by a novel morphotype. Whole-genome and 16S rRNA gene phylogenetic analyses placed this cyanobacterium within the recently described genus Limnofasciculus (Coleofasciculaceae). Genome-based species delimitation metrics fell below accepted thresholds for bacterial species delineation relative to Limnofasciculus baicalensis, the only formally described species in the genus to date, supporting recognition of the cyanobacterium from Shenandoah River as a distinct species. Furthermore, the two Limnofasciculus species exhibited marked structural differences in the Box B helix of the 16S–23S ITS region. Comparative genomic analyses revealed a genome size similar to L. baicalensis and a conserved core gene repertoire alongside substantial divergence in biosynthetic gene cluster composition. Neither species contains biosynthetic gene clusters associated with the production of known cyanotoxins. Based on morphological, phylogenetic and genomic evidence, we describe Limnofasciculus delicatus sp. nov., supported by light microscopy and whole-genome characterization.

DOI: https://doi.org/10.1111/1758-2229.70377

An Inventory of Potomac Basin Entities with a Role in Sustainable Water Resources Management

Authors: Heidi Moltz Published in March 2025

The Potomac Basin Comprehensive Water Resources Plan (2018) outlines a shared vision of sustainable water resource management in the basin. Responding to a Plan recommendation, the Interstate Commission on the Potomac River Basin (ICPRB) created an inventory of organizations with a role in sustainable water resources management in the basin in 2022. The inventory was the product of an iterative process initiated by ICPRB staff with input from the plan’s Advisory Committee.

2025 Washington Metropolitan Area Water Supply Study: Demand and Resource Availability Forecast for the Year 2050

Authors: S.N. AHMED, K. BENCALA, S. NUMMER, C.L. SCHULTZ, AND A. SECK | Pub: # ICP-596 | Published in December 2025

This is the eighth in a series of studies by the Interstate Commission on the Potomac River Basin (ICPRB) Section for Cooperative Water Supply Operations on the Potomac (CO-OP) to evaluate the adequacy of the Washington, DC, metropolitan area (WMA) water supplies to meet expected water demands over the coming decades. The WMA has a unique, cooperative water supply system that was established more than 40 years ago by a set of regional agreements signed by the Fairfax County Water Authority (Fairfax Water), the Washington Suburban Sanitary Commission (WSSC Water), the Washington Aqueduct Division of the U.S. Army Corps of Engineers (Washington Aqueduct), the District of Columbia, and CO-OP. One of the requirements of the regional agreements is that every five years, such an evaluation be conducted. The current study’s planning horizon is 2050. It provides decision-makers with the following:

Forecasts of water demands for the WMA, taking into account projected demographic and societal changes that may affect future water use
Forecasts of water availability, considering the potential impact of changes in meteorological conditions and upstream consumptive use of water on system resources
An evaluation of the ability of existing and planned system resources to meet the forecasted demands

A fact sheet is available with a summary of the report’s findings >>>

Stream Health in the Chesapeake Bay Watershed, 2018 – 2023 Update

Authors: C. Buchanan, R. D. Jepsen, and E. Young. | Pub: # ICP25-1 | Published in December 2025

Non-tidal stream health in the Chesapeake Bay watershed is evaluated every six years to accommodate rotational sampling schedules of the major stream monitoring programs. A 2024 Data Call brought in stream macroinvertebrate data and related water quality and habitat data collected by eighteen monitoring programs in the watershed between 2018 and 2023, the fourth 6-year interval. The percentage of stream miles with healthy macroinvertebrate communities increased an estimated 2,026 miles in this interval, for a 1.4% improvement over the previous interval. High flows in 2018 and 2019 and the COVID19 pandemic in 2020 disrupted monitoring activities, and stream evaluations in the interval are based on less data. Since 2000 – 2005, the first 6-year interval, stream miles with healthy macroinvertebrate communities have increased 10.3% overall, and an estimated two-thirds (66.7%) of stream miles in the watershed are now thought to be healthy. Improvement is unevenly distributed in the watershed. Stream health appears to be improving in eight more rural western and southern bioregions; it is not improving in two central, heavily populated bioregions, and is degrading in two eastern, highly agricultural bioregions. Additional data and new criteria for separating streams from rivers have slightly changed the percentages of healthy streams for previous intervals but not the overall findings. The average rate of improvement is 3.4% over a 6-year interval, which suggests the revised Stream Health goal can be achieved in 2024 – 2029, the next 6-year interval, as ongoing efforts to restore and protect the Bay watershed continue.

Learn more about Chessie BIBI >>>

Is Hot Drought a Risk in the US Mid-Atlantic? A Potomac Basin Case Study

Authors: C. L. Schultz, A. Seck, S. N. Ahmed Published in June 2025

This paper was published in the Journal of the American Water Resources Association (Volume 61, Issue 3, June 2025)

Interannual variability of streamflow will increase under a future climate, but at the regional scale, there is uncertainty regarding changes in drought severity, and in particular, changes in extreme hydrological drought that could necessitate new water supply infrastructure. This is due to the wide range of regional projections for precipitation and the challenge of estimating statistics in a nonstationary climate. We assess changes in annual streamflow in the Potomac River Basin using a nonparametric approach based on a climate response function and the K-nearest neighbor method, which is relied on to construct time series of sufficient length to compute extreme quantile values. Our results indicate that future Potomac River flows will be impacted by “hot drought”, that is, increasing drought severity caused by rising temperatures coupled with natural variability in precipitation. Average precipitation is projected to increase in the Potomac basin by 9%–12% in the period 2039–2069 and by 11%–16% by 2070–2099. Average streamflow increases more modestly, by 4%–7% in 2039–2069 and by 2 to 9% in 2070–2099, whereas annual flows in an extreme drought year decrease by 3 to 26% in 2039–2069 and by 2%–49% in 2070–2099, assuming a medium sensitivity of flow to temperature. Our approach can provide multi-model consensus inputs for water supply planning models to support decision-making regarding new infrastructure.

DOI number: https://onlinelibrary.wiley.com/doi/10.1111/1752-1688.70031

Evaluating time-lagged relationships between groundwater storage and river discharge using GRACE-based data: insights from the Potomac Basin

Authors: AJ Villaruel, Alimatou Seck and Cherie Schultz Published in July 2025

This paper was published in the Environmental Research Communications (7 075003)

This study evaluates the utility of a recently available GRACE-based groundwater drought index (GDI) in supporting regional water supply management, with application to the Potomac River Basin, in the U.S. Middle Atlantic region. As the primary drinking water source for the Washington Metropolitan Area (WMA), effective management of the Potomac River’s resources is critical, especially in the context of climate change, with the expected increase in severity and frequency of extreme events. Our analysis integrates 22 years of data, including GRACE-based groundwater storage (GWS) index estimates, river discharge (Q) measurements, and meteorological records, to investigate trends and predictive relationships between past GWS, as determined by the GRACE-based drought index, and streamflow. Seasonal Mann-Kendall trend analyses consistently identified severe declining trends in groundwater storage (GWS), as well as moderate declines in minimum streamflow and well water levels over the past 22 years. Granger Causality (GC) tests revealed significant time lags of 49 weeks to 22 months at weekly and monthly scales, respectively depending on a region’s hydrogeomorphic characteristics. Vector Autoregressive (VAR) Models and Forecast Error Variance Decomposition (FEVD) highlighted the variable contributions of precipitation and temperature to the GWS-Q relationship, revealing a strong autoregressive component of Q, but also reveal that GWS plays an important role, and this role increases with time. These findings underscore the interconnectedness of groundwater and surface water systems and the importance of integrated predictive models to enhance water management strategies. Incorporating GRACE-based seasonal groundwater forecasts into drought preparedness tools could bolster efforts to mitigate regional climate change impacts and improve the resilience of water resources in the Potomac River Basin. While practical use of native GRACE data has been challenging for local, small-scale applications, this study demonstrates the utility of the GRACE-based GDI in forecasting low flows and informing regional water resource management decisions during droughts.

DOI: 10.1088/2515-7620/ade36f

Methods and Procedures for Calculating the Chesapeake Basin-wide Index of Biotic Integrity (Chessie BIBI)

Authors: E. Young, R. D. Jepsen, and C. Buchanan | Pub: # ICP25-2 | Published in December 2025

This document describes the methodology used to calculate and report the Chesapeake Basin-wide Index of Biotic Integrity (Chessie BIBI) for stream macroinvertebrates. It provides a transparent record of data handling, analytical approaches, and publication of results and data. This methodology underlies the preparation of the “Stream Health in the Chesapeake Bay Watershed, 2018 – 2023 Update” report (Buchanan et al. 2025).

Potomac Basin Trends in Water Use

Authors: Heidi Moltz, Andrea Nagel, and Stephanie Nummer-Fantozz Published in March 2024

This pamphlet summarizes projected reported water withdrawals and consumptive use (CU) in the Potomac basin. This work, along with the results
presented in the Potomac Basin Reported Water Use pamphlet and Wallace et al. (2023), addresses the technical recommendation, “Report on Basin-Wide Water Uses, Projected Demands, and Consumptive Demands” in the Potomac Basin Comprehensive Water Resources Plan (Recommendation 3.3.2 A).