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<br />j. Introduction <br /> <br />Isohyetal maps of average annual precipitation have long been and <br />continue to be a backbone and starting point for many climatic, <br />hydrologic and basic watl?r resource and land use studies. In Colorado <br />there have only been a few satisfactory attempts during the past several <br />decades to complete such a map. The most recent and most complete <br />attempt to date was the "Normal Annual (and Summer and Hinter Season) <br />Precipitation Map of Colorado, 1931-1960" completed during the 1960s by <br />the U. S. Weather Bureau. This two map set has proven credible in <br />depicting, with local accul^acy, the great diversity of the precipitation <br />climate of Colorado. <br />The 1931-60 Map set, which was printed by the 1I. S. Geological <br />Survey and distributed by the ColoriJdo Water Conservation Board, has <br />been out of print since the early 1970s. Although still considered <br />relatively accurate, the years have gradually taken a toll on the <br />credi bil ity of thi s product. Research results and computer simul ati ons, <br />such as the orographic precipitation model of Rhea (1978), have <br />presented justification for cha'llenl)ing the accuracy of the original <br />analysis in portions of the Colorado Rockies. Al so, considerably more <br />precipitation data have been collected since 1960 improving the data <br />base for the analysis. <br />In 1982, the Colorado Climate Center, with funding from the <br />National Oceanic and Atmospheric Administration National Climate Program <br />Office and the Colorado State University Agricultural Experiment <br />Station, initiated the effort to update the Colorado precipi tation map. <br />The interagency Colorado Hydrometeorological COTTlnittee provided peer <br />review throughout the project. Drafting and plrinting services were <br />donated by the U. S. Geological SU1^Vey. <br />