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Baseline Hydrologic Monitoring Plan — Hansen Project 6 <br />2.1.2 PRISM Spatial Climate Data Sets <br />Spatial climate datasets were obtained from the PRISM Climate Group of the Northwest Alliance for <br />Computational Science & Engineering (NACSE) based at Oregon State University. The PRISM <br />(Parameter - elevation Regressions on Independent Slopes Model) interpolation method is an analytical <br />model that uses data from NWS and SNOTEL climatic monitoring stations and a digital elevation model <br />(DEM) to generate spatially distributed estimates of climate. <br />These spatial climate data sets are developed on 30- aresec (- 800 -m, or —2,600 -ft) grids are the official <br />spatial climate data sets of the U.S. Department of Agriculture. PRISM calculates a climate—elevation <br />regression for each DEM grid cell, and stations entering the regression are assigned weights based <br />primarily on the physiographic similarity of the station to the grid cell. Factors considered are location, <br />elevation, coastal proximity, topographic facet orientation, vertical atmospheric layer, topographic position, <br />and orographic effectiveness of the terrain. Station data are spatially quality controlled, and short- period- <br />of- record averages adjusted to better reflect the estimation period (1981 — 2010). <br />The PRISM datasets are publicly available as GIS shapefiles. Data for the 1981 -2010 mean monthly <br />precipitation, mean monthly temperature, and mean annual precipitation were downloaded from the PRISM <br />site (http: / /www. prism. oregonstate .edu /normals /10- 25 -13). The datasets were provided in latitude - <br />longitude (Lat -Long) using NAD83 datum and were brought into ArcGIS and plotted as point data in <br />Colorado State Plane Central NAD27. <br />The PRISM datasets are considered to be a reliable representation of climate for the site, since they utilize <br />existing data from nearby met stations and also account for local topographic and orographic effects. <br />2.1.3 Precipitation Best Engineering Estimate <br />Based on the climate data from the Guffey 10 SE station and the PRISM spatial data sets, the best <br />engineering estimate (BEE) of mean annual precipitation for Hansen Project is 16.5 inches per year (Figure <br />2). The majority of precipitation occurs in July and August, averaging approximately 3 inches per month, <br />while little precipitation occurs in December, January, and February (averaging approximately 0.5 inches <br />per month) <br />4153A.140129 Whetstone Associates <br />