THE ACCURACY OF WATER USE FORECASTS: EVALUATION AND IMPLICATIONS¹

Abstract

: Forecasts of 1980 river basin water use presented in the reports of the 1960 Senate Select Committee on National Water Resources and in the Water Resources Council's First National Water Assessment of 1968 were compared to estimates of actual use in 1980 to assess the accuracy of efforts to forecast future water use. Results show that the majority of the forecasts were substantially in error. In general, the First National Assessment forecasts erred by a smaller margin, but tended to repeat the regional patterns of overestimation (underestimation) exhibited in the Senate Select Committee forecasts. Moreover, forecasts of the two groups that came within 20 percent of the 1980 withdrawals, in general were accurate, not because of superior prediction, but because of offsetting errors in forecast components. This performance leads us to conclude that water use forecasts, regardless of the time‐frame or the forecast method employed, are likely to always be highly inaccurate. Accordingly, if such forecasting efforts are to be of value in contemporary water resources planning, forecasters should direct their attention toward methods which will illuminate the determinants of the demand for water.

Developing decision support systems for integrated coastal management in the tropics: Is the ICM decision-making environment too complex for the development of a useable and useful DSS?

“…Some argue that the most valuable aspect of a complex model is its capacity for educating those involved in management (Osbourne et al, 1986). The educational role covers the identification of the variables subject to management control, the nature of interactions among these variables and the assessment of the relative impacts of alternative management initiatives.…”

USE AND MISUSE OF COMPLEX MODELS: EXAMPLES FROM WATER DEMAND MANAGEMENT1

“…However, this complexity can be a real liability because it may take much labor to collect data needed to make the MAIN Systems run (e.g., one may need information on up to 330 categories of water use in the residential, commercial, industrial, and public sectors in which to develop solutions for problems unanticipated by the modeling effort. This is especially true for models that have a very short-term horizon during which confidence is warranted (Osborn et at., 1986;Konikow and Bredehoeft, 1992).…”

A Review of the United States' Past and Projected Water Use

“…When data are not available, analysts typically must calculate informed estimates as best they can. Few researchers have examined national or regional historical water‐use estimates or future water‐use assessments in part because these data are not comprehensive (Osborn et al ., ).…”

“…Limitations do arise when using historical water‐use estimates to inform future water‐use assessments, in part because assumptions about future conditions may not be realistic. The few studies that have taken up a review of future water‐use assessments found that, over the long term, actual events often failed to mimic the scenarios used to derive future water‐use estimates (Osborn et al ., ; Brown, ; Christian‐Smith et al ., ). These studies are either dated (Osborn et al .…”

“…These studies are either dated (Osborn et al . ) or their review focuses on national water use (Brown, ; Christian‐Smith et al ., ); consequently, there are not many details on how water‐use estimates and projections have unfolded at regional levels.…”