Public Tools Developed by USACE -- 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 hydrologic data which comprise a sequential structure of recurring measurements. The insights found in this data can reveal underlying factors and patterns that impact design and optimization of critical infrastructure.

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 of a suite of tools and web applications for repeatable, quantitative analysis of this data.

The Time Series Toolbox provides a diverse set of capabilities for time series analysis. It enables analysis of trends and seasonality, using regression techniques and statistical methods to identify and define these patterns. The tool also allows for nonstationarity 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 engineering design, as there has been increasing evidence that the impacts of a changing climate undermine the assumption that observed data are unchanging in time (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 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. 

Nonstationarity Detection Tool

Stationarity, or the assumption that the statistical characteristics of time series data are constant through time, enables the use of well-accepted statistical methods in water resources planning and design. By assuming stationary hydrologic conditions, data observed in the past can be used to characterize future conditions. However, recent scientific evidence shows that—in some places, and for some impacts relevant to the operations of the U.S. Army Corps of Engineers (USACE)—climate change and human modifications of the watersheds are undermining this fundamental assumption, resulting in nonstationarity.

The Nonstationarity Detection (NSD) Tool enables the user to apply a series of statistical tests to assess the stationarity of annual instantaneous peack streamflow data and gage height time series at any United States Geological Survey (USGS) streamflow gage site with more than 30 years of record. The tool aids practitioners in identifying statistically based evidence of nonstationarity in annual instantaneous peak streamflow datasets. The tool enables practitioners to visualize time series data being analyzed in conjunction with statistical analysis based on 12 different tests for nonstationarity. The tool also plots shifts in sample mean and variance at nonstationarities detected.  By identifying years where multiple tests are indicating a significant change in sample mean, variance and/or overall statistical distribution users can identify strong nonstationarities. In addition to applying statistical tests targeted at detecting nonstationarity, the tool also allows users to conduct monotonic trend analyses using three tests for statistically significant trends and two methods for characterizing the directionality of identified trends based on slope.

The Nonstationarity Detection Tool was developed to support USACE Engineer Technical Letter (ETL) 1100-2-3, Guidance for Detection of Nonstationarities in Annual Maximum Discharges. The tool provides consistent, repeatable analytical results that support peer review processes.

Climate Hydrology Assessment Tool

USACE took the first step toward developing policy and guidance around projected changes to climate hydrology and how these changes might affect water resources project planning, design, construction, operations, and maintenance by releasing Engineering and Construction Bulletin 2014-10, Guidance for Incorporating Climate Change Impacts to Inland Hydrology in Civil Works Studies, Designs, and Projects.  This was superseded by ECB 2016-25, released on 16 Sept 2016, and then by ECB 2018-14, the current guidance.

ECB 2018-14, released on 10 Sept 2018, supersedes and updates ECB 2016-25. The qualitative analysis required by this ECB includes consideration of both past (observed) changes as well as potential future (projected) changes to relevant hydrologic inputs as part of a first-order statistical analysis of the potential impacts to hydrologic elements of the study. This analysis can be very useful in considering future without project conditions (FWOP) and the potential direction of climate change. Examples of this type of analysis is provided in Appendix C.

The Climate Hydrology Assessment Tool (CHAT) allows users to easily access climate model data and develop repeatable analytical results, thereby reducing potential error and accelerating the decision-making cycle. CHAT is designed to support a variety of uses related to inland hydrology, such as the development of flood risk registers or adaptation pathways. This tool allows users to analyze state-of-the-art hydrologic and climate model information, such as ranges and trends in climate-modeled annual maximum monthly streamflow at the watershed scale.  CHAT also generates visualizations suitable for use in report-generation.  CHAT’s capabilities further enable decision-makers, planners, and engineers across a spectrum of missions to assess and mitigate potential impacts of future climate change on their equities.