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.. ~.::?'J~ -,,:;....:f.,~_;l1 ;:::..~':n!C ~:.;r.';.?! ~',.,:.~~L" . ...~},;.."'. "~;~::-:;:., '" .... . ..;'7.~j ...:.;.'.. OJJ385 This material is taken from Casebook onl~ydrological Network uesign Practice~ World Meteorological Drgani=ation. WMO - No. 324, 1972. ., IV - 4.3 REPORTING NETWORK FOR FORECAST AND WARNING PURPOSES: A CASE REPORT ON PLANNING IN THE USA by M, A, Kohler" Introduction The prediction and warning of impending nooding is a major objective of the National Weather Service in the United Slates. Flood forecasts are prepared for over 1800 key river stations and for numerous intermediate points. Moreover. forecasts of river stage and discharge are issued daily for approximately 325 of these poin ts to serve water management and other operational requirements. River forecasts are based on reponed precipitation, snowpack and temperature as weU as on quantitative forecasts of meteorological elements. Reported river stages, once the main information input, are now used chiefly to monitor and adjust forecasts_ Modest progress is being made to automate the reporting network and radar is being used in a limited way to estimate areal precipitation. There are also plans to use earth-synchronous satcllites as a communications relay in the reporting system. The existing reporting network in the United States is largely the result of circumstances. As limited increases in funds became available, they were applied to those areas where requirements seemed most urgent (often reacting to the chance occurrence of a recent major flood) and station locations were usually dictated by availability of communications facilities and observers_ An increasing number of stations have been automated (telemetry via radio or telephone line) of recent years and it has become obvious that a reliable 24-hour warning service wiU not be possible until the co-operative, part-time observers are replaced by a fully automated reporting system. The technique described in this section was used to develop the preliminary design for such a system. The principal objective of the study was to develop a network for which the required resources were considered reasonably feasible and in which the geographical distribution of stations would reflect future forecast requirements. It can be said with assurance that the reduction in Oood damage alone would far outweigh the total cost of the hydrological forecasting service. including tile proposed networks. Initial de<...;sions There were several decisions mJde ill conncxion with the srudy which should bc cited. It was decided that the design should be independent of the J.pPlicJtion of the possible quantitative evaluation of precipitation by radar. Although it is hoped thaI radar will be so applied ill some Cjreas by the mid-seventies, it is expected that point meas- urements of precipitation will be nceded to "c~librate" the radar pattern - in other words, radar will provide improved accuracy of areal precipitation, but will not relieve the requirement for reports of precipitation, snow cover and other elements. With respect to hydrometric stations, it was decided that river stage should be reportcd for aU forecast points and that the added cost for precipitation reports would be economically justiflcd from prac- tically all these stations. Finally, it was decided that the requirements for elements other than river stage and pre. cipitation could be provided through add-on sensors at such stations. In other words, all network stations would report precipitation and the station configuration was based on the accuracy requirements for this element. . National Wealher Ser....ice. NOAA, USA. 1--1--;""""':,~;