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Show Susanne M. Clement Department of Geology Kent State University Kent, OH 44242 THE HYDROLOGIC REGIME OF THE BONNEVILLE BASIN AT THE LAST GLACIAL MAXIMUM. We use a Local Climate Model ( LCM), previously developed at Kent State University, to solve climate for modern and last glacial maximum ( LGM) conditions ( 18ka) in the Bonneville Basin. The solution area occupies approximately 290,000 km2 between 37 N to 43 N and 111 W to 115° W and is represented by a 5km x 5km grid. Point- wise solution of the LCM are compared to observed temperature and precipitation at four climate stations located within the solution domain for validation of the modern mean values. We also compare the results to the natural variability of climate. The assessment of natural variability is based on sets of five year averages chosen at random from the observational record. We examine the ratio of precipitation and difference in temperature from one period to another and conclude that model means are unbiased estimators of the station means. When comparing modern temperature solutions to those for the LGM we find that LGM climate was cooler on average by 3° C. During the LGM winter ( Nov - Mar) the average temperature is as much as 6° cooler while the LGM summer ( May - Sep) is 1.5° cooler ( Figure la). Total wet season precipitation ( Nov- Mar) is estimated to be 200% higher on average for the LGM, while dry season ( May- Sep) precipitation is estimated to be 175% higher ( Figure lb). Using a runoff model driven by the output of the climate model we find, as shown in Figure 2, that runoff during the LGM was 800% higher and confined to the period May- October; but, was almost absent during the cold season ( Nov- April). This differs from the modern situation in which significant runoff occurs in winter. This change is expected if runoff is trapped as snowpack and ice. Nearly all LGM runoff is generated as snowmelt in just two months ( July and August) with July runoff being 20 times modern and a smaller contribution ( still up to four times modern) in September and October. |
