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498 Seventh Ave, 11th Floor
New York, NY 10018

(212) 539-7000

City of Raleigh Drought Forecasting

The City of Raleigh’s water supply reservoirs experienced prolonged drawdowns during an extended dry period from 2010 through 2012. The Raleigh City Council asked the Public Utilities Department (CORPUD) to provide reports on the City’s water supply status along with a recommendation regarding whether mandatory conservation measures were necessary to ensure the City’s water supply reliability in the event of an intensifying drought. CORPUD turned to Hazen and Sawyer to help it address these concerns.
The forecast is based on an OASIS model of the Neuse River basin. This model uses 80+ years of historical hydrology, along with simulated reservoir operation rules and demands, to provide a statistical analysis of how current reservoir levels and service area demand conditions are likely to interact over the forecast period.

Hazen developed a 12-month look-ahead water supply forecast (i.e. drought forecast) using the Neuse River Basin Hydrologic Model. The forecast uses the 80+ years of historical hydrology in the model to provide a statistical analysis of how current reservoir levels and service area demand conditions are likely to interact over the forecast period. The probability that the City’s reservoir levels might drop below various trigger thresholds can be easily read for any point within the forecast period. This concise visual format supported the City’s decision to delay the implementation of mandatory conservation measures.

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Through this project, the City of Raleigh’s Water Shortage Response Plan was enhanced to incorporate reservoir storage forecasts that estimate the probability that the City’s reservoir levels might drop below various trigger thresholds.

Furthermore, forecasts were provided for both of the City’s reservoir systems, helping the City balance withdrawals from each system in a manner that minimized the overall risk of a supply shortage.

A drought forecast template was developed that allows for rapid production of water supply forecast reports on an as-needed basis. Forecasts were repeated six times over 2010-2012, and in each case it was determined that mandatory drought restrictions were not necessary. The result was a win-win for the City and its customers; the City avoided revenue losses from mandatory conservation measures, and the City’s customers were spared from enduring prescriptive conservation measures at a time when they were not needed to ensure continued water supply reliability.

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In addition to updated forecasts based on current conditions, the forecast model could also be used to pre-generate results for a range of initial conditions, such as a display of the probability of storage falling below 20% in the next 24 months as a function of time of year and initial storage.

Project Outcomes and Benefits

  • Water Supply Forecasts produced using models developed by Hazen and Sawyer allow the City of Raleigh to base mandatory conservation decisions directly on risk of future drought. Together with the Water Shortage Response Plan, these forecasts ensure that water use restrictions are applied when they are risk-justified and reduce the potential for false drought alarms and associated undesirable financial and political consequences.
  • Institution of standard forecast procedures, such as the forecast template, streamlines the production of forecasts and acts to institutionalize knowledge about true water supply risks. This knowledge helps prevent overreaction by utilities, government, and stakeholders to visually-intimidating drought-depressed lake levels.