Soil Moisture. Precipitation. These officials said that probabilistic forecasts provide a range  of potential outcomes and their likeliness. Experts Said the Corps Could Not Have Predicted or Prevented Flooding Due to Extreme Weather in 2011 and Its Release Decisions Were Appropriate

Experts who participated in our meeting discussed the above normal  snowpack in the mountains and the plains, but they agreed the flood was  triggered by the extreme rain in eastern Montana in May and June 2011. The  experts agreed that no existing forecasting tools, including those used by  the Corps and NOAA, could have accurately predicted the extreme  rainstorms that occurred in Montana more than a week in advance. One of the experts said it would have taken  several months for the Corps to release enough water from the reservoirs  to make space for the runoff from the rainstorms and melting snow, and  that action also could have resulted in downstream flooding. Experts Did Not Suggest Changes to the Master Manual

Experts who participated in our meeting agreed that the Corps does not  need to change the Master Manual due to the 2011 flood or 2012 and  2013 drought, noting that there are no obvious deficiencies in the Master  Manual. Other experts who  participated in our meeting noted, however, that if the Corps could  develop improved forecasting tools, it might be useful to evaluate whether  changes to the Master Manual would help the Corps to act on information  from the new tools. However, it is important to note that the hydrologic data  systems discussed by the experts are not managed by the Corps but by  other federal agencies as part of nationwide efforts to gather this data. DEP  officials said that a similar tool could help the Corps better manage other  reservoir systems, such as along the Missouri River. Some of the experts said that  the Corps can achieve better outcomes for the basin using probabilistic  techniques than their current methods. Stakeholders Were Generally Satisfied with Corps’ Communication during the Flood and Drought

During both the 2011 flood and the subsequent drought, the Corps  communicated with Missouri River stakeholders in a variety of ways,  which most stakeholders we interviewed said were effective. Nearly all  stakeholders we interviewed were generally satisfied with the Corps’  communication with them during these events, saying that the information  they received from the Corps was timely and sufficient for their purposes. However, there was no consensus among  stakeholders on these suggestions. A few stakeholders suggested that  the Corps communicate any uncertainty associated with its release  estimates. Corps officials also said that having separate conference calls for agency  officials and elected officials and media is feasible and that they would  consider this in the future. Conclusions

The extreme flood of 2011 followed by severe drought in 2012 and 2013  created challenging conditions on the Missouri River for the Corps. Experts who participated in our meeting agreed that the Corps made  appropriate release decisions during the flood and drought, given the  circumstances. However, the experts agreed that techniques such as  probabilistic forecasting have the potential to improve the Corps’ ability to  make release decisions in nonextreme events. Probabilistic forecasting  could allow the Corps to make better risk-based decisions and provide  increased benefits to residents in the Missouri River basin, such as higher  reliability of water supply, increased flood protection, small increases in  hydropower production, and easier implementation of variable river flows  to create fish and wildlife habitats. However, the Corps currently uses  deterministic forecasting methods, and Corps officials told us that they  have not assessed the pros and cons of using probabilistic techniques  because they are not sure that the benefits of more sophisticated  probabilistic modeling techniques would outweigh the difficulty of creating  the models or explaining the new methods to the stakeholders in the  Missouri River basin. Recommendation for Executive Action

To ensure the U.S. Army Corps of Engineers considers a full range of  forecasting options to manage the Missouri River mainstem reservoir  system, we recommend that the Secretary of Defense direct the  Secretary of the Army to direct the Chief of Engineers and Commanding  General of the U.S. Army Corps of Engineers to evaluate the pros and  cons of probabilistic forecasting techniques that could improve the U.S.  Army Corps of Engineers’ ability to anticipate weather developments, and  to evaluate whether forecasting changes are warranted. Appendix II: Objectives, Scope, and Methodology

This report describes (1) experts’ views on the Corps’ release decisions  during the 2011 flood and 2012 and 2013 drought; (2) additional actions,  if any, experts recommend to improve the Corps’ ability to make future  release decisions; and (3) stakeholders’ views on how the Corps  communicated information during the flood and drought and  improvements, if any, stakeholders suggest. To obtain expert views on the Corps’ information and release decisions,  we convened a meeting of experts to discuss these issues.
Why GAO Did This Study

The Missouri River stretches from western Montana to St. Louis, Missouri. The Corps manages six dams and reservoirs on the river to provide flood control and for other purposes, such as recreation and navigation. The Corps bases reservoir release decisions on the guidance in the Master Manual. In the 2011 flood, the Corps managed the highest runoff volume since 1898, resulting in record reservoir releases. Subsequently, drought occurred in the basin in 2012 and 2013.
GAO was asked to review the Corps' release decisions and communication during the flood and drought. This report examines (1) experts' views on the Corps' release decisions; (2) experts' recommendations to improve the Corps' release decisions; and (3) stakeholders' views on the Corps' communication, as well as any suggested improvements. GAO worked with the National Academy of Sciences to convene a meeting of nine experts to discuss the Corps' data, forecasts, and release decisions. GAO also interviewed 45 Missouri River basin stakeholders, including state and local agencies, among others, to discuss their views on the Corps' communication. The views of stakeholders are not generalizable.

What GAO Found

Experts who participated in a GAO-sponsored meeting agreed that the U.S. Army Corps of Engineers (Corps) made appropriate release decisions during the 2011 flood and 2012 and 2013 drought affecting the Missouri River basin, given the severity of these events. These experts acknowledged that the flood was primarily due to extreme rain in eastern Montana in May and June 2011. The experts agreed that no existing forecasting tools could have accurately predicted these extreme rainstorms more than a week in advance. One of the experts also said that the Corps would have needed several months to release enough water from the reservoirs to have sufficient space for the runoff that occurred in 2011, and predicting an extreme runoff year that far in advance is beyond the current state of science. Moreover, the experts agreed that the Corps appropriately followed the drought conservation procedures in the Missouri River Mainstem Reservoir System Master Water Control Manual (Master Manual), which sets out policies for managing the river. The experts agreed that the Corps does not need to change the Master Manual in response to the 2011 flood or subsequent drought. However, some of the experts noted that if the Corps develops improved forecasting tools, it might be useful to evaluate whether changes to the Master Manual would help the Corps to act on information from the new tools.
The experts suggested that improving data systems and introducing new runoff forecasting techniques could improve the Corps' ability to make release decisions in less extreme events than the 2011 flood. These data systems—such as streamgages, weather radar, precipitation gauges, soil moisture monitoring, and monitoring for snow on the plains—are not managed by the Corps, but by other federal and state agencies, which creates challenges beyond the Corps' control. The experts agreed that probabilistic forecasting techniques—which correct for unknown initial conditions using statistical techniques and provide a range of potential outcomes and their likeliness—could help the Corps manage risks better than their current methods that create one forecast estimate. One of the experts said that probabilistic methods could provide greater benefits, such as higher water supply reliability, increased flood protection and hydropower production, and easier implementation of variable flows to create fish and wildlife habitats. Probabilistic techniques are currently used by New York City to support reservoir releases to manage flood risk and meet water quality goals without adding expensive new filtration equipment. Corps officials said that they have not considered using probabilistic techniques in the Missouri River basin because they are not sure the benefits would outweigh the difficulty of creating the models or explaining the new methods to their stakeholders.
During both the flood and drought, the Corps communicated with Missouri River stakeholders in a variety of ways, which most stakeholders GAO spoke with said were effective. Most stakeholders were generally satisfied with the Corps' communication, saying that the information they received from the Corps was timely and sufficient for their purposes. Most stakeholders had at least one suggestion on how the Corps could improve communication; however, there was little consensus on any one suggestion. A few stakeholders suggested that the Corps hold separate conference calls to discuss sensitive response-related issues. Corps officials said that they would consider this in the future.

What GAO Recommends

GAO recommends that the Corps evaluate the pros and cons of incorporating new forecasting techniques into its management of the Missouri River reservoirs. The Department of Defense concurred with the recommendation.