Demand for water and water demand forecasting

How are statewide forecasts for water demand made in Florida? That was one of my jobs when I was the Administrator of the Office of Water Policy for FDEP. It was easy: add up the five separate water management district forecasts. To my regret, it turned out to be a lousy way of making forecasts.

For example, the October 1999 “Annual Status Report” on regional water supply planning said that water demand was 7.2 billion gallons a day and would increase to 9.2 billion gallons a day by 2020. Wrong, wrong, wrong. This is demonstrated in the December 2012 version of the annual report which says that current annual demand was only 6.5 bgd and that year 2030 demand (ten years later) would 7.9 bgd. Florida is still forecasting a lot of demand growth despite the failure of the previous predictions.

Because elaborate water supply plan forecasts prepared by the water management districts have been wildly inaccurate, we are forced to rely on common sense(!). Obviously, some areas will see demand growth. Others must reduce withdrawals to restore Florida springs and minimize saltwater intrusion. For total statewide demand, I believe that water use twenty years from now will be about the same as today. For a bunch of reasons:

  1. Per capita trends of reduced water use show no sign of slackening.
  2. Urban uses still have a lot of unused potential for improving efficiency.
  3. The population of Florida will not increase as fast as the current forecast.
  4. Higher population densities will reduce the acreages of irrigated grass.
  5. Eventually, the legislature will require efficient landscape irrigation and enact a water-efficient plumbing code.
  6. Significant acreages of irrigated agriculture in Florida will be displaced by urbanization, which tends to use less water per acre than irrigated crops.
  7. Citrus diseases will continue to shrink citrus acreage. (A 30% reduction since 1996.)
  8. A reformed sugar program might even be created that would both save consumers money and reduce south Florida water use.

That’s the story of future water supply, as I see it. Water quality is different. Just as was recognized in 1971, “Water quality is a far graver problem in the long run than is water quantity.

Comments

Demand for water and water demand forecasting — 6 Comments

  1. thanks for the post on forecasting. this is very helpful. Who are others working on more accurate forecasts for cities or counties, using price and population as explanatory variables, especially since the economic meltdown and halt in construction. The District are just interested in permitting, so they estimate high to cover their permitting needs.

    And the quality of what is coming out of the ground?

    best regards, Richard Weisskoff, author: Economics of Everglades Restoration”

  2. All of the incentives in the water planning and supply world are on the side of forecasting ever-growing demand for water. I don’t mean this as an aspersion on integrity of water managers. They just naturally wanna make ultra-sure there is lots and lots of water in the future. So their forecasts err on the high side, or the very high side. Politicians, as a separate matter, like to dole out money for essential public services like water supply.

  3. Projections are typically based on BEBR medium projections and historic per capita water use. Both of these have changed dramatically in recent years. This should not be seen as a failure. Rather, the decreased per capita water use, to the exent that it has declined due to conservation and reuse, should be viewed as a signficant accomplishment by Floridians. We should continually be concerned with making the best possible projections, but to some extent it is not critical that the projections be completely accurate with respect to time. What is critical is identifying what levels of withdrawals cause unacceptable impacts, regardless of when they might happen. Florida must plan for responsible growth. Periodic updating of projections helps us better dial in the when part.

  4. I think you have some good thoughts about this, Jim. However, I don’t think the too-high forecasts are as small a problem as you do. High forecasts result in wasted water supply planning efforts or even enormous expenditures on un-needed water supply projects. That can be real money and real damage to water resources. Imagine, for example, if Florida had built a series of hyper-expensive seawater desalination plants that some proposed as a water supply answer. Based on experience, forecasts should always come with a statement like: “This is our best guess of future demand. Our best guesses in the past have been pretty inaccurate and generally way high. Try not to make big expenditures based on these forecasts until you really have to.”

    • I think both of you make good points. Public supply is the lion’s share of the forecasted increase, but the use of historic per capita has missed some significant achievements with conservation and beneficial reuse. When foreseeable conservation is established in recent permits or regulatory/incentive strategies that predict a reduced per capita, the Districts can elect not to adjust the projections. So caveating the projection methodology and the approx. “when” is definitely appropriate in the case. There is also value to having project options that encompass a range of potential needs for “when” occurs.

  5. Water demand is always interesting. But, I still get a feeling that agriculture gets some of the blame game on useage and I don’t see any blame on tourist atractions, hotels, and golf courses. ‘Water quality is a far graver problem on the long run than is water quantity’ is the best statement that should worry all conservationist. There are storm water runoff wells in Ocala, Orlando, and Dade County that are doing damage and no one fights it. Florida Ground Water Association has been voiceing their concerns to FDEP about this situation and is getting little traction. No one seems to care. Everything off the street runs into these wells and into the aquifer. Everything else is regulated to death but not these runoff wells.