This document discusses trends in evapotranspiration and evaporation in the Coon Creek Watershed District over the past decade. It shows that excess precipitation from evapotranspiration and evaporation has decreased based on Thornthwaite and evaporation coefficient models. This decrease in excess precipitation is expected to result in less natural recharge and loss of lakes and wetlands in the watershed district.

1. Evapotranspiration

2. Review Of Current Chapter
25” of PET annually (approx. 83% of annual ppt)
35” of Evaporation annually (UM value)
Growing Season:
Operating deficit of 8.9” (2.7” PET + 6.2” EC)

3. TREND ANALYSIS
EVAPOTRANSPIRATION
Thornthwaite
Excess has 18
16
y = -0.5259x + 9.0047
decreased over 14
Excess Precip (in)
12
the past decade 10
8
6
4
2
0
-2
2000 2001 2002 2003 2004 2005 2006 2007 2008 2009
Year
Yearly Thornthwaite Excess Period of Record Avg
Linear (Yearly Thornthwaite Excess)

4. TREND ANALYSIS
EVAPORATION
Evaporation Coefficient
Evaporation 8
6
y = -0.5259x - 1.2353
excess has 4
Excess Precip (in)
2
decreased over 0
-2
-4
the past decade -6
-8
-10
-12
2000 2001 2002 2003 2004 2005 2006 2007 2008 2009
Year
Yearly Excess Period of Record Avg Linear (Yearly Excess)

5. Implications
Coefficients for the District are “published”
values but should be monitored
Excess precipitation is dependent on volume of
precipitation received

6. Expectations
Less Excess Precipitation
= Less Natural Recharge
Less Excess Precipitation
= Losing Lakes and Wetlands

7. Questions?
Thank You
Coon Creek Watershed District