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<br /> <br />i <br />1 <br /> <br />1 <br /> <br /> <br /> <br /> <br /> <br />r <br /> <br />~J <br /> <br /> <br /> <br /> <br /> <br />III. PRECIPITATION REG~ <br />As the collection of historic record vegetation data is tied to the prevailing precipitation <br />regime which directly impacts vegetation growth in the historic record vegetation <br />community, documentation of the prevailing precipitation regime is required to assess <br />the representative nature of the growing season precipitation. From this assessment, a <br />determination can be made of the representative nature of the growing season. From <br />this determination, sampling of the historic record vegetation community can occur in <br />low, average, and high precipitation years, thereby evaluating and establishing the <br />growth potential and range in growth of the representative vegetation community. <br />The historic record study area is located within the North Fork Valley, an incised <br />riverine drainage valley trending east-west. Two basic types of climate are <br />characteristic of the azea of the West Elk Mine (which includes the Historic Record <br />Study Area); semi-arid and undifferentiated highlands (MCC, 1996). The climate of <br />the mine and surrounding area is characterized by a wide temperature fluctuation; from <br />below freezing in winter, to very warm in the summer months. Precipitation in the <br />area is provided by Pacific Ocean weather systems and is most frequent and reliable <br />during the winter months. <br />The National Weather Service (NWS) has collected precipitation data in the vicinity of <br />the mine since 1905. The most complete record of precipitation is from the Paonia 1 <br />SW station located in Paonia, Colorado. This station has been in operation since 1905, <br />and has wllected climatic information for 65 individual years at this same location. <br />Table 1 presents a summary of precipitation data collected from the Paonia 1 SW <br />station from 1905 through 1995. A review of the data illustrates that precipitation is <br />lowest during the summer months (June through August) and higher from the autumn <br />through late spring. The months with the highest average precipitation are October and <br />March. As is illustrated by the maximum and minimum values (as well as the reported <br />standard deviations), precipitation on a monthly basis can be highly variable. Our <br />calculations yielded an average mean precipitation total of 11.47 inches for the months <br />October through May, from 65 years of record at the Paonia 1 SW station. Based on <br />precipitation records from all locations of the Paonia 1 SW station from 1905 through <br />1995, CDMG calculated a total "pre-growing season" precipitation total of 11.08 <br />inches. This CDMG value was accepted as the mean value for "pre-growing season" <br />precipitation. From this average, comparisons of individual yearly precipitation <br />affecting specific growing seasons can be made. <br />Table 2 illustrates the precipitation prior to the 1996 growing season for the Paonia 1 <br />SW station. Total "pre-growing season" precipitation was 7.78 inches. This translates <br />into a 29.78 percent negative departure from normal precipitation amounts (11.08 <br />inches) and a very dry growing season for vegetation in 1996. <br />-5- <br />