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lIl)'~I'JO J ......i.. (') . Report. 1948, and the Upper Colorado Reoion Comprehensive Framework Study. .ill.l. Frost Data Frost data was generally unavailable for most of the study period. Thus, mean frost temperatures were calculated and used as limits for those years of either nonexisting or non-computer recorded data. The mean monthly temperatures that roughly equate to spring or fall frosts or beginning and end of growing season, were adjusted to bring the average consumptive use rate or the average growing season length into agreement with those in the Enoineerino Advisorv Commission's Report. 1948, and the Upoer Colorado Reoion Comprehensive Framework Study. 1971. Table 2 summarizes temperature adjustments made to the temperature data (average monthly) and selection of mean temperatures to represent spring (28"F) and fall (32"F and 28"F) frost events. . a e - JUS ments to emperature ata Sub-basin Weather Temoerature Adjustment 1nclusive Station Fall Fall Years Spring 2S"F 32"F 28"F Upper Gunnison 53 55 53 1906-74 Gunnison North Fork & Paonia 50 52 50 1906-74 South Fork Lower Montrose 48 52 49 1906-74 Gunnison Upper Montrose 54 56 53 1906-74 Uncomoahore Lower De lta 53 52 49 1906-74 Uncompahgre Montrose 1906-30 --- --- --- T bl 2 CRSS Ad' t T D Shortened Growino Seasons . Much.of irrigable land in the Upper Colorado River Basin is dependent on spring runoff for its irrigation supply. Runoff comes in spring and early summer, Therefore, supplies in late summer diminish, resulting in a shortened growing season for crops such as pasture and alfalfa. This shortened growing season varies in length from year to year throughout the basin. The CRSS study considered the yearly fluctuation in local streamflow for determining the length of the shortened growing season, The study relied on the methodology used in the Enoineerino Advisorv Commission's Report. 1948, and the Upper Colorado Reoion Comorehensive Framework Studv, 1971. The primary means for estimating the crop's consumptive use, under shortage conditions, was to establish a cutoff date which would end the growing season two to three weeks before the estimated date of final irrigation.