This tutorial was not designed to provide guidance for applying downscaled climate model projections to inform an analysis. Each Federal, State, and Local agency should follow agency specific guidance for including possible future climate change information in hydrologic analysis. This tutorial highlights tools in HEC-HMS that aid modelers in making use of gridded meteorologic datasets and utilizing the new Ensemble compute option to organize many simulations. 

Create Simulation Runs for CMIP5 Climate Model Projection Datasets

The following steps describe how simulation runs were created. The Ensemble Analysis compute requires existing simulation runs be created first before they can be added to an ensemble analysis. You could explore parameter and modeling method uncertainty by creating multiple basin models and varying the modeling options (for example, use different different loss models) and parameter values. The ensemble analysis will help you organize the simulations and combinations of basin models and climate model projection datasets. 

  1. Two Control Specifications were created for simulating the calibrated basin model with the CMIP5 Climate Projection datasets. The HistoricalPeriod Control Specification had a time window from 01 October 1970 - 30 September 2005. The FuturePeriod Control Specification had a time window from 01 October 2005 to 30 September 2099. Both control specifications were set to use a simulation time-step of 3-hours.
  2. Simulation runs were created for each of the CMIP5 Climate Model Projection datasets. The figure below shows all 20 CMIP5 Climate Projection simulation runs. All simulation runs used the same basin model that was calibrated using the Livneh precipitation and temperature data. 
  3. The amount of output saved by the simulations was customized using the simulation's output selection tool. As shown in the figure below, the Selected Output option was chosen. The custom Results table was used to select all results for the MF_TuleR_S20 (high elevation subbasin) and TuleR_S10 (low elevation subbasin) subbasin elements and the ReservoirInflow junction element (this is the inflow into Success Dam). Customizing the results written to the output reduced file sizes by more than half.

This step took approximately 30 minutes to complete.

Create Ensemble Analysis Simulations

The following steps describe how Ensemble Analysis simulations were created.

  1. Open the Ensemble Analysis manager from the Compute menu.
  2. Create a New Ensemble Analysis and make sure the Analysis Type is set to Simulation Runs.
  3. Three Ensemble Analyses were set up in the HEC-HMS project. One Ensemble simulation contained only RCP 4.5 CMIP5 Climate Projection simulation runs for the historical period. Precipitation and temperature data are the same regardless of the RCP scenario through the end of 2005. The following figure shows the Component Editor for the CMIP5_historical ensemble analysis.
  4. The following figure shows the Component Editor for the CMIP5_future_RCP85 ensemble analysis. Notice the correct simulations are selected. 
  5. One of the strengths of the ensemble compute is its ability to summarize important information. As shown below, the output Results editor was configured to save results for the MF_TuleR_S20 and TuleR_S10 subbasin elements and the ReservoirInflow sink element. The program will extract results from the individual ensemble members and save the selected results to the ensemble output file. For example, ensemble analysis results for the CMIP5_historical simulation are written to the CMIP5_historical.dss file located in the main project directory. 

This step took approximately 30 minutes to complete.

Continue to Analyze Results and Identify Trends from the Historical Period (1971 - 2005) and Future Period (2006 - 2099).