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One of the implications of climate change for ESP is that climate events far into the past may not be representative of the present. Therefore, the number of historical years of data that should be used in ESP simulations is limited, perhaps to only 20 or 30, depending on how fast climate changes. Also, it is essential to keep existing hydrometeorological data systems operating, even if there already is an extensive historical record. Continuing to operate existing data systems is necessary so that recent data may be used in ESP and so that model parameters (which are also a function of climate) may be updated. Yet, because of the current federal budget pressures, proposals to reduce data networks are being made to meet budget targets.

An alternative to using historical hydrometeorological data to drive ESP is to use stochastically generated data. This involves making assumptions about the hydrometeorological processes that are not necessary if historical data are used. On the other hand, if climate is changing and if data networks are reduced, the stochastic alternative may be needed. One advantage of the stochastic approach is that forecasters would have more control over the current climatic regimen and could consider not only the effects of long-term change but the current state of the atmosphere, oceans, and continents.


Most of the figures and examples and many of the ideas expressed in this paper are based on the work of Gerald N. Day, who is responsible for technical oversight of NWS ESP procedures and who is serving as the program manager for the NWS WARFS initiative. I gratefully acknowledge his contribution and advice.


Brazil, L. E., and M. D. Hudlow. 1980. Calibration procedures used with the National Weather Service River Forecast System. Pp. 371-380 in Preprint Volume, IFAC Symposium on Water and Related Land Resources Systems, Case Institute of Technology, Case Western Reserve University, Cleveland, Ohio, May 28-31.

Day, G. N. 1985. Extended streamflow prediction using NWSRFS. American Society of Civil Engineers, Journal of Water Resources Planning and Management 111(2):157-170.

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