Ingredients-based Climatology and Future Projections of Extreme Precipitation Events Using a Numerical Weather Prediction (NWP) Framework

Project ID: 6917
Principal Investigator: Raymond Caldwell
Research Topic: Managing Hydrologic Events
Priority Area Assignments: 2012 (Climate Change and Variability Research), 2013 (Climate Change and Variability Research)
Funded Fiscal Years: 2012 and 2013
Keywords: ingredient-based, climate change, numerical weather prediction, extreme precipitation events

Research Question

1. Using a numerical weather prediction (NWP) framework, what impact does climate change have on the atmospheric conditions and geographical dependency of extreme rainfall events in the Colorado Front Range?

PRIORITY AREA: 3.06 - High priority from Long-Term Document


(1) Leverage the Colorado Front Range (CFR PACE) study to extend and transfer Kelly Mahoney's research using WRF to Reclamation staff

(2) Identify atmospheric and geographic forcing of extreme rainfall events in the Colorado Front Range

(3) Evaluate the effects of climate change on extreme precipitation events in the Colorado Front Range

(4) Preliminary results of scale dependencies using North American Regional Climate Change Assessment Program
(NARCCAP) and Weather Research and Forecasting (WRF) model output at varying resolutions

Need and Benefit

A current priority research area for the Science and Technology Program includes climate change adaptation. Recent research suggests that one of the most significant impacts of climate change may be changes in the frequency of extreme events including precipitation and associated flooding (e.g., Fowler and Hennessy 1995' Bukovsky and Karoly 2011). In the Front Range of Colorado, extreme precipitation events are concentrated in the warm season and are often driven by convective storms under upslope conditions, anchoring the storms along the eastern escarpment of the Rocky Mountains. The resolution of global climate models, however, are incapable of capturing local convective activity as they are typically run at spatial resolutions of several tens to over a hundred kilometers. This research will capitalize on the ability of regional climate models to dynamically downscale global climate model simulations. In addition, the research will compare the output of different modeling systems to provide insight into the spatial and temporal differences between models based on scale.

The CFR PACE project (Assessing the potential for changes in warm season extreme precipitation events across the Colorado Front Range in future climates; pace.html#1) investigates the changes in warm season extreme precipitation events in future climates using a high-resolution numerical weather prediction (NWP) model. Extreme precipitation events drive decisions related to water resources, including dam safety, flood risk and mitigation, and reservoir operations. Extreme precipitation events are modulated by many environmental factors that are predicted to change in future climates. The CFR PACE project has identified 10 extreme rainfall events and examined changes in atmospheric physics associated across the individual storms (e.g., changes in freezing level and surface hail accumulations due to warming low levels). The current research will build upon the framework of the CFR PACE project by using the downscaled WRF simulations to identify the primary meteorological ingredients and diagnostics contributing to extreme rainfall events. In addition, the current research will enhance collaboration with researchers from the National Center for Atmospheric Research (NCAR) Colorado Headwaters Project (CHP) to acquire historical and climate-perturbed simulations for the period 2000-08. Using the storm identification methodology from the CFR PACE project, extreme precipitation events will be extracted from the CHP data to evaluate scale and model sensitivity. Additional storms from NARCCAP could be investigated outside of the Front Range focus region of the CFR PACE project.

The downscaled climate model information will help to contribute to the proper depiction of meteorological forcing mechanisms responsible for extreme precipitation events. Understanding these contributing variables to extreme precipitation events and how they might change under future climate conditions is important to assessing the potential risks of more frequent or more intense storms. Furthermore, identification of regions with increasing/decreasing potential for extreme rainfall events could serve as an important decisionmaking consideration for future planning and adaptation activities in the western U.S., specifically for Reclamation's dam safety and operations for major projects such as the Colorado-Big Thompson. While the current study is focused on the Front Range of Colorado, the methodology developed may easily be adapted and applied at Reclamation sites across the western U.S. where the contributing factors for extreme precipitation may be significantly different from the Front Range.

Contributing Partners

Contact the Principal Investigator for information about partners.

Research Products

Bureau of Reclamation Review

The following documents were reviewed by experts in fields relating to this project's study and findings. The results were determined to be achieved using valid means.

Will extreme rainfall change in Colorado's future? (final, PDF, 236KB)
By Raymond Caldwell Victoria Sankovich Jason Caldwell
Publication completed on September 30, 2013

This bulletin summarizes the research results and potential application to Reclamation's mission.

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Last Updated: 6/22/20