Correlations between past climate and streamflow in 5 streams in the state of Minnesota
are investigated. The rivers are the Straight, Baptism, Zumbro, Clearwater, and
Mississippi Rivers. Runoff measured over periods of up to 37 years are correlated with
precipitation, air temperature, wind, and dew point temperature. The overall objective is
to obtain relationships which can be used in long-term water budget estimates and which
use only readily available input parameters without calibration. A seasonal (3 month)
time frame produced the closest fit for the linear regressions without time lag. Although
the watershed sizes varied greatly, the 3 month period seemed sufficiently long to average
long term processes such as infiltration, evaporation, and groundwater flow. An equation
was found for each season (3 months) separately for each of the final river records
chosen. Winter (December, January, February) regressions utilize only the precipitation
data; the spring regressions use air temperature and precipitation; summer and fall
regressions are found with precipitation and an evaporation term which used a
combination of air temperature, dew point temperature, and wind. The coefficients in the
regresssion equations are related to watershed characteristics.
Statistics for the seasonal linear regression equations include a root mean square
error (RMSE) between observed and predicted runoff values and a coefficient of
variability (CV). The RMSE error values, found from the sum of the squares of the
errors (SSE), range from 0.111 in/mo to 0.692 in/mo. The coefficients of variability
(CV), a measure of the relative error of the fitted runoff values, range from 0.237 to
The seasonal regression equations are used to project future runoff averages if a
climate change occurs. For this purpose the Goddard Institute for Space Studies (GISS)
values for the "2xC02 climate scenario", i.e. the climate projected after a doubling of
atmospheric CO2, are applied to the linear runoff regression equations. The projections
are that the spring runoff values will decrease by 16 % to 35 % while the other seasons
will experience an increase in streamflow between 3 % and 50 %. Annual runoff will not
change dramatically; decreases (3 to 4 %) are projected for the Baptism and Mississippi
River basins, while an increase (9 %) is projected for the Zumbro River. The results are
in the range of changes predicted by other investigations using very different techniques.
Since predictions are based on equations found with past records, it is implied that the
land cover will remain unchanged in the 2xC02 environment. This may be unrealistic
and needs further investigation.
US Environmental Protection Agency, Environmental Research Laboratory
Kletti, Laura L.; Stefan, Heinz G..
Empirical Relationships Between Runoff, and Climate Parameters: An Analysis for Minnesota.
St. Anthony Falls Hydraulic Laboratory.
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