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<br />1. INTRODUCTION
<br />
<br />1.1 Objective
<br />In 1959, the Senate Select Committee on National Water Resources was appointed
<br />to assess the nation's water supplies in relation to anticipated demand through the
<br />year 1980. The conterminous United States was pivided into twenty-two water resource
<br />regions, and the following five principal categories of water management studied:
<br />1. Streamflow regulation
<br />2. Improved water quality
<br />3. Increased water use efficiency
<br />4. Expanded use of underground storage
<br />5. Expanding natural water yield by desalting, weather modification,
<br />and reduction of evaporation losses.
<br />The Select Committee report in January 1961 found that five of the twenty-two
<br />,
<br />water resource regions would be using all available water supplies by or before 1980.
<br />All five regions for which short water resources were projected are in the western
<br />United States.
<br />Subsequent to the Select Committee report, November 1961, the Congress of the
<br />United States authorized the Bureau of Reclamation to explore the potential of weather
<br />modification for increasing water resources in their continuing role of water resources
<br />management.
<br />During the past twelve years, the Bureau of Reclamation has sponsored many
<br />research programs to further the understanding of cloud physics, and how the preci-
<br />pitation process may be altered by artificial means. A major goal of this effort
<br />has been to determine the"feasibility of increasing water resources by weather modi-
<br />fication on an operational basis.
<br />Several operational cloud seeding programs have indicated that increases in
<br />seasonal precipitation and subsequent runoff on the order of 10 to 15% could be
<br />expected. These, or similar percentage increases have often been applied to aver-
<br />age seasonal precipitation in estimating the potential increased water resources to
<br />be attained from cloud see~ng in a drainage basin. Since seasonal precipitation
<br />varies considerably from year to year, this approach does not provide information
<br />to state what the potential increased water resources, and subsequent benefits,
<br />might be in dry years as opposed to wet years. Such an approach also does not take
<br />into account the frequency of occurrence of precipitation enhancement. In addition,
<br />models have been recent+y developed relating seeding effects to key air mass pa-
<br />rameters. Mountain station precipitation records can now be analyzed in conjunction
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