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<br />first and second most severe droughts in Appendix E are often related to the 1930s and 1950s. <br /> <br />Wet periods are not quite as uniform in time. <br /> <br />5.2 Snowpack and Streamflow <br />The dominant source of water for streamflow and reservoir storage is the winter <br /> <br />snowpack. However, the snowpack has a limited number of observation sites and the spatial <br /> <br />variation of snowpack (SN) in elevation and horizontally is often large in Colorado. The <br /> <br /> <br />streamflow is also a complex variable to relate to snowpack. The streamflow (ST) can vary <br /> <br />significantly with the weather which controls melting and with precipitation which occurs after <br /> <br />April 1 which is the date of the snowpack (SN) used in this study. The streamflow (ST) is further <br /> <br />complicated by both water stored in reservoirs to be released later, by transmountain diversions <br /> <br />which move water from one drainage to another and by water used for irrigation in the basin. The <br /> <br />analyses discussed below will however allow dry and wet years to be identified. <br /> <br />The April 1 SPI for snowpack (SN) (called SSI to distinguish it from SPI) is given for 66 <br /> <br />locations in Appendix B in which the observing sites have been grouped by river basins. The sites <br /> <br />in Appendix B have been selected since they are used in the application to predict streamflow <br /> <br />(ST). More sites are available to establish a climatology of snowpack (SN) but the relationship to <br /> <br /> <br />streamflow (ST) was a factor in the selection of sites for this report. The average SSI for each <br /> <br /> <br />basin is given in Figure 11. Historic observed streamflow (ST) for selected locations in each basin <br /> <br /> <br />are given in Appendix C and the reconstructed streamflow CST) for a more limited time period are <br /> <br /> <br />given in Appendix D. The reconstructed streamflow (ST) in Appendix D show that the winter of <br /> <br />1977 was uniformly a dry year and it is the driest year since 1960 to use as a reference. The other <br /> <br />really widespread dry events were in 1966 and 1981. Other low streamflows (ST) were more <br /> <br />23 <br />