Climate-Impacted Hydrology

Managing hydrologic extremes due to climate variability is an essential mission of water management agencies. Climate change requires water resources managers to move from an equilibrium—or stationary—paradigm to one of constant evolution that recognizes the dynamic nature of physical and socioeconomic processes.

USACE infrastructure, operations, safety and maintenance programs are facing growing stresses caused by aging infrastructure, hydrologic nonstationarity, urban growth, coastal development, evolving navigation and shipping practices, changing agricultural practices, and increasing recognition of the need for ecosystem restoration. USACE must ensure that its systems and projects will remain adaptable and sustainable over time even if the frequency and severity of extreme hydrologic events may change.

Hydrological tools and methods supporting climate change adaptation planning and implementation, as discussed on the Hydrology to Support Adaptation page, is a major focus of Brekke et al. (2009) and subsequent discussions by the interagency Climate Change and Water Working Group (USACE 2011). The team is developing processes, methods and guidance for hydrology used in climate change impact assessments and adaptation planning and design.

Time Series Toolbox

Time series data is of particular importance to the United States Army Corps of Engineers (USACE) as many engineering decisions rely on climate, weather, or financial data which take a sequential structure of recurring measurements. The insights found in this data can reveal underlying factors and patterns that impact plan formulation and design.

In particular, climate change is one of many global changes USACE faces in carrying out its missions to help manage the nation's water resources infrastructure. The measurement and analysis of climate data over time can aid in the decision-making process—one heavily reliant upon assumptions about future supplies, demands, weather, climate, and operational constraints at varying space and time scales. To better enable this required analysis and to empower deeper exploration of time series data more broadly, USACE has developed a suite of tools and web applications for repeatable, quantitative analysis of this data (U.S. Army Corps of Engineers, 2011).

The Time Series Toolbox (TST) provides a diverse set of capabilities for the time series analysis of preloaded USGS data and user-provided datasets. Primarily, it enables a deeper analysis of trend measurement and seasonality, using regression techniques and statistical methods to identify and define these patterns. The tool also allows for nonstationary detection through various statistical measures, such as the Lombard Wilcoxon and Kolmogorov-Smirnov tests, to evaluate change points in the data. This nonstationarity analysis is vital to studying climate data, as there has been increasing evidence that highlights the impacts of a changing climate (IPCC, 2013). Finally, the tool enables users to select and visualize the most appropriate time series model for the given dataset.

The TST User Manual offers guidance on the tool’s capabilities and user interface. Along with an explanation of how to easily navigate the application, it includes a discussion of the technical concepts and statistical tests incorporated into the TST, such as in-depth descriptions of the nonstationary tests and time series models.   

Climate Hydrology Assessment Tool (CHAT)

When releasing Engineering and Construction Bulletin (ECB) 2014-10, Guidance for Incorporating Climate Change Impacts to Inland Hydrology in Civil Works Studies, Designs, and Projects, USACE took the first step toward developing guidance around projected, climate-driven changes to hydrology and how these changes might affect water resources project planning, design, construction, operations, and maintenance. This original ECB was superseded by ECB 2016-25 (16 September 2016). The current version of the guidance is contained in ECB 2018-14 (19 August 2022), which supersedes and updates previous guidance provided in ECB 2016-25.

The analysis required by ECB 2018-14 includes consideration of both past (observed) and potential future (projected) changes to hydrologic variables relevant to the feature being designed, the measure being evaluated, or the study being conducted. The ECB 2018-14 assessment enables a project development team to consider the impacts of climate change as part of their decision-making process. ECB 2018-14 output helps characterize the future without project conditions (FWOP) and to qualitatively assess the residual climate change-driven risks to a feature, measure, and/or study area. Results from a ECB 2018-14 climate change assessment can be incorporated into USACE planning risk registers and can be applied to justify the identification and incorporation of added resilience to climate change impacts and adaptation pathways.

The CHAT is designed to support ECB 2018-14 analysis. The tool allows users to visualize downscaled global climate model (GCM)-based output specific to their study area. It also supports the development of defensible and repeatable analytical results, thereby ensuring that USACE can effectively use the information throughout their decision-making processes. The CHAT allows users to visualize derived output based on state-of-the-art GCMs and hydrologic models. Output includes ranges and trends in modeled historic and future (projected) streamflow, temperature, and precipitation variables. The CHAT also supports the development of report-quality graphics. The tool’s capabilities further enable decision makers, planners, and engineers across a spectrum of missions to assess and mitigate the potential impacts of climate change.