CORRELATIONS OF CLIMATE AND STREAMFLOW IN 3 MINNESOTA STREAMS

Correlations between four climate parameters and streamflow in three M innesota streams were investigated. Runoff values measured over period s of up to 37 years were correlated with precipitation, air temperatur e, wind, and dew point temperature. The overall objective was to exami ne if relationships can be obtained which require only readily availab le input parameters without calibration. Such relationships would be o f great use, e.g. to compute future lake water budgets without recours e to more detailed and complex hydrologic runoff models. Monthly, seas onal, and annual time frames were investigated. A seasonal time frame using 3 month averages gave the closest fit for the linear regressions without time lag. Although the watershed sizes varied from 360 to 49, 600 square kilometers, the 3 month period seemed sufficiently long to average long term hydrologic processes such as infiltration, evaporati on, and groundwater flow. An equation was found for each season (3 mon ths) for each of the rivers. Winter (December, January, February) regr essions required only precipitation data; spring regressions required air temperature and precipitation; summer and fall regressions were fo und with precipitation, air temperature, dew point temperature, and wi nd speed. The coefficients in the regression equations were related to the watershed characteristics, The r(2) values were highest for the Z umbro River in spring (0.69) and lowest for the Baptism River in winte r (0.14). Root mean square error values ranged from 2.8 mm/mo for the Mississippi River in winter to 18 mm/mo for the Baptism River in sprin g. The coefficients of variability (CV) ranged from 0.24 to 0.52. Over all the results were disappointing but not all bad. Climate parameters without watershed parameters can characterize runoff only within limi ts. To project possible future runoff averages the GISS GCM-values for the 2 x CO2 climate scenario were applied to the seasonal runoff regr ession equations. The projections were that the spring runoff values w ould decrease by up to 35% while in the other seasons streamflows woul d increase by up to 50%. Annual runoff would not change significantly enough to be predictable. The results were in the range of changes pre dicted by other investigations using very different techniques. Since predictions were based on equations found with past records, it was im plied that the land cover would remain unchanged in the 2 x CO2 enviro nment. This may be unrealistic and needs further investigation.