DecadeScale Precipitation Variations

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Decade-Scale Precipitation Variations
in the Great Plains
Jurgen Garbrecht
USAD - ARS Grazinglands Research Laboratory El
Reno, Oklahoma
2
?
Why study precipitation
Primary climatic driver of agriculture and water
resources.
Water is limited and limiting resource.
Climatic system driven by global-scale phenomena
and subject to variations.
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Precipitation varies at different scales
Daily
Monthly
Annual
Decade
Century
Longer
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- Regional character of d-s P variations.
- Impact on stream flow.
- Seasonal aspects of d-s P variations.
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Decade-Long Precipitation Variations
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C A N A D A
Great Lakes
R o c k y
M i s s i s s i p p i
M o u n t a i n s
R i v e r
M E X I C O
Gulf of Mexico
8
C A N A D A
1
2
4
3
5
6
a
9
7
b
a
Atlantic Ocean
Pacific Ocean
b
8
Gulf of Mexico
MEXICO
Increased precipitation in 1990-1999
Increased precipitation in 1980-1999
No increased precipitation at the end of the 20th
century
9
6
OK, TX, AR, LA
11-yr MA of Annual Precipitation
Standardized AP
10
5
KS, NE, MO, IO
11-yr MA of Annual Precipitation
Standardized AP
11
SD, MN
4
11-yr MA of Annual Precipitation
Standardized AP
12
80
80
Climate Division 5 Oklahoma
1895-1979
1980-1999
60
Probability of Occurrence
40
33
33
33
20
12
8
0
Dry Year
Wet Year
Average Year
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Impact of the Decade-Scale Increase in
Precipitation on Stream Flow
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C A N A D A
1
2
4
3
5
6
a
9
7
b
a
Atlantic Ocean
Pacific Ocean
b
8
Gulf of Mexico
MEXICO
Increased precipitation in 1990-1999
Increased precipitation in 1980-1999
No increased precipitation at the end of the 20th
century
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SD
NE
WY
Elkhorn
Big Blue
IA
Little Blue
KS
Neosho
MO
CO
Walnut
Verdigris
OK
Climate Division
River Basin
State line
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R2 of precipitation versus streamflow
Drainage area sq. mi.
Period of record
River name
1929-99
6900
0.48
Elkhorn, NE
1933-99
4447
0.59
Big Blue, NE
1930-99
2350
0.64
Little Blue, NE
1922-99
4905
0.78
Neosho, KS
1922-99
1880
0.64
Walnut, KS
1921-99
2982
Verdigris, KS
0.77
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Mean annual precipitation
Increase
prior- 1980 in
1980- 1999 in
River name
? P
26.7
11
Elkhorn, NE
24.0
Big Blue, NE
27.8
30.4
9
Little Blue, NE
27.6
29.6
7
37.8
9
34.6
Neosho, KS
Walnut, KS
36.2
39.9
10
37.2
40.1
Verdigris, KS
8
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Mean annual streamflow
Increase
River name
prior- 1980 cfs
1980- 1999 cfs
?Q
2046
Elkhorn, NE
1098
86
Big Blue, NE
787
39
1095
428
Little Blue, NE
369
16
Neosho, KS
2560
36
3494
Walnut, KS
801
35
1081
2283
Verdigris, KS
1685
35
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Climate Divisions in Oklahoma
Tulsa
OKC
N
Little Washita River Experimental Watershed
Glover Watershed
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Chickasha
Great Plains Experiment Station
Anadarko
USGS stream gage
River
ARS rain gage
Little
National Weather Service rain gage
Washita
OKLAHOMA
N
10 Km (6.2 mi.)
Marlow
Situation Map
Little Washita River Experimental Watershed
21
11-yr moving average of annual runoff and
precipitation depth
155
935
Runoff
130
Precipitation
885
105
835
80
785
Runoff mm
Precipitation mm
55
735
30
685
Little Washita River Watershed, OK
5
635
1950
1960
1970
1980
1990
2000
Year
22
11-yr moving average of annual runoff versus
precipitation depth
150
125
100
75
Runoff mm
50
25
Little Washita River Watershed, OK
0
650
700
750
800
850
900
950
Precipitation mm
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11-yr MA of Annual Retention vs Precipitation
Depth
Little Washita River Watershed, OK
Runoff
Retention
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Climate Divisions in Oklahoma
Tulsa
OKC
N
Little Washita River Experimental Watershed
Glover Watershed
25
11-yr moving average of annual runoff and
precipitation depth
700
1400
Runoff
Precipitation
600
1300
500
1200
Runoff mm
Precipitation mm
400
1100
Glover Watershed, OK
300
1000
1960
1970
1980
1990
2000
Year
26
11-yr MA of Annual Precip-Runoff
Glover Watershed, OK
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Glover Watershed, OK
Runoff
Retention
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Seasonal pattern of decade-scale precipitation
variations
Case application using divisional precipitation
data in southwestern Oklahoma
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11-Year MA of Annual Precipitation
Southeastern Oklahoma
Annual Precip mm
Year
30
11-Year MA of Seasonal Precipitation
Southeastern Oklahoma
JAS
JFM
AMJ
OND
Annual
Departure from mean
Year
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Conclusions
At the end of the 20th century, the majority of
the Great Plains was under the influence of the
longest and strongest decade-scale precipitation
increase of the entire century.
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Conclusions
Streamflow runoff from watersheds in the
Nebraska, Kansas and Oklahoma responded very
sensitively to the decade-scale precipitation
increase.
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Conclusions
Due to the disproportionate increase
of streamflow during the decade-scale precipitatio
n increase, crop and forage production only
benefited from a portion of the precipitation
increase.
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Conclusions
The strong fall and winter increase in
precipitation associated with the decade-scale
variations favors fall and winter crops.
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Conclusions
The decade-scale precipitation increase
has helped meet the water needs of a growing
economy and society. However, the increased
demand for water has made the economy and society
more vulnerable to decade-scale variations in
precipitation.