Making Sense of Climate Projections and Data Using USACE Hydroclimate Applications

The United States Army Corps of Engineers (USACE) has developed the Climate Hydrology Assessment Tool (CHAT) and Time Series Toolbox (TST) to provide the community with methods to analyze projected climate data. These tools support the analyses required by Engineering and Construction Bulletin (ECB) 2018-14, which provides guidance for consideration of observed and projected changes to hydrology and the potential effects of these changes for USACE Civil Works water resources project planning, design, construction, operation, and maintenance. The CHAT and TST ease the computational burden associated with evaluating climate-changed hydrology and meteorology by allowing for efficient, repeatable analyses to incorporate climate change into studies supporting infrastructure vulnerability reduction and resilience improvement.

The CHAT enables users to analyze and visualize simulations of streamflow, temperature, and precipitation time series over a historical period as well as future (projected) outputs of climate-changed hydrology and meteorology. The data available in CHAT are outputs from 32 Global Climate Model (GCM) simulations from the Coupled Model Intercomparison Project Phase 5 (CMIP5). Meteorological variables have been statistically downscaled using the localized constructed analogs (LOCA) method. The gridded, downscaled meteorological variables are aggregated to the Hydrologic User Code (HUC) Level-8 level, allowing temperature and precipitation variables to be presented for each HUC-8. Streamflow simulations are generated in two steps. The LOCA-downscaled meteorological outputs are first used as input in the Variable Infiltration Capacity (VIC) hydrologic model and gridded VIC outputs are then routed through a stream network using the mizuRoute model. This processing allows streamflow outputs to be presented on a stream segment basis in the CHAT. All variables are then aggregated from the daily scale to the monthly and annual scales to provide inter-model summary statistics that can easily be incorporated into a report for Civil Works projects and other similar applications.

The CHAT provides several visualizations of climate variables such that users can analyze the range, trend, and epoch-based changes of simulated streamflow variables from 32 GCMs. Incorporated into the newest version of the CHAT are the latest robustness metrics introduced in the IPCC Sixth Assessment Report (AR6). These robustness metrics assess inter-model agreement on (1) the directionality of the climate signal and (2) whether projected changes in the climate variables are significant relative to the variability of simulated historical outputs. These robustness metrics provide additional confidence to users about the projected trends in climate variables.

The Time Series Toolbox (TST) provides a diverse set of capabilities for the time series analysis of both preloaded United States Geological Survey (USGS) streamflow gage site data and user-uploaded data. Once uploaded, the user can explore different components of time series analysis. The tool specifically facilitates the detection of trend, seasonality, and nonstationarity within the data. Users can also explore their data through three different time series models: autoregressive integrated moving average (ARIMA), exponential smoothing (ETS), and linear models (TSLM). These models can be applied to the forecasting, error handling, interpretation, and decomposition of climate data.

Recently, studies have been conducted to broaden the applicability of the TST. Experiments on tidal gage, precipitation, and temperature data have revealed best practices for analyzing change point detection in varying types of climate data. For example, the study on tidal gage data highlighted the importance of understanding autocorrelation in cyclical time series data and how to appropriately preprocess this data. Through the study on precipitation and temperature data, methods for detecting nonstationarity were evaluated, along with experiments to discover any concurrent change points throughout different variables from the same location.

This poster will provide a review of the CHAT and TST tools, highlighting their capabilities in facilitating climate-changed hydrology and meteorology assessments for USACE Civil Works projects and other hydroclimate applications.