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5.0 Drought and Wet Periods Occurrence and Description Drought is such a complex phenomena that different aspects must be viewed somewhat differently. The definition of drought given above for a single location is quantitative and clear for a monthly continuous series of observations. The analysis of snowpack based on April I values will provide another view of drought using one data point each year, A similar thing occurs when the interest is in just the summer or spring or any fixed interval oftime. This section includes discussions of drought and wet periods from several different points of view. 5.1 Precipitation Dry and wet conditions can be characterized for Colorado by examining the fraction of stations in the state which are dry or wet at the same time. The spatial extent of dry or wet conditions is shown in Figure 7 for the period of the early 1890s through 1996 for averaging time scales of3, 6, 12,24 and 48 months. Fewer stations were reporting observations in the 1890s so the results during this period are indicative but not as definitive as in the period after the very early 1900s. Notice in Figure 7a for the 3 month time scale that the fraction changes rapidly in time and peak values exceed 0.80 on 4 occasions for dry conditions with SPI < -1 (1890, 1893, 1939,1981) and on 7 occasions for wet conditions with SPI > 1 (1891, 1905, 1906,1914, 1941, 1952, 1995). As the averaging periods or time scales become larger, graphs show less rapid changes, the dry or wet periods last longer, and the maximum fraction is reduced. The 24 month graph in Figure 7d has been used to characterize dry and wet periods that affect approximately 40% of the state during the episodes. These are given in Table 4. The periods are not uniformly dry or wet and often have a portion of the period in which the opposite condition increases a bit and then decreases. A sum of the durations of each type show that wet existed for 64 years and 16