Uncertainty in Long-Term Water Demand Forecasting
- Jack Kiefer - Hazen and Sawyer
Long-term forecasts of water demand serve as critical inputs to water utility planning efforts and decision making, and they play many roles in those processes. Traditionally, long-term forecasts have been and continue to be used for identifying the timing and magnitude of future water supply needs. Over the last two to three decades, the growing recognition and emphasis on the amount of water that can be conserved through greater efficiency has also made long-term forecasts important from a demand management perspective. The role of long-term demand forecasts in affecting decisions about water supply investments, including investments in “alternative” supplies such as enhanced efficiency and water reuse, leads to further implications for water rate making and pricing strategies.
Uncertainties about the future, as well as about the causes of historical and recent trends in water usage patterns, can affect (a) how long-term water demand forecasts are constructed and (b) why long-term water demand forecasts are seldom realized with very high degrees of accuracy. Inaccurate forecasts can lead to sure costs to water utilities, water rate-payers, and even to the environment. For example, over-building of supply and water treatment capacity can lead to stranded capital assets, higher water rates than might otherwise be necessary, and additional stress on watersheds. On the other hand, under-investment could result in imposition of water shortage restrictions and economic damages from water shortages. These risks, the ways they are affected by planning uncertainties, and how utilities cope can be perplexing and present a complex challenge for the drinking water community.
This paper will present an update on Water Research Foundation Project 4558, Uncertainty in Long Term Water Demand Forecasts. The paper will review key uncertainties related to forecasting long term demand for water resource and infrastructure planning. Using the results of a water utility survey, the review will describe contemporary long-term forecasting practices and how different forecasting methodologies affect the ways in which one can incorporate future uncertainties into the forecasting process. The paper will also provide additional perspectives from the drinking water community regarding strategies to account for and manage the potential consequences of these uncertainties.
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