decade-scale precipitation variations in the great plains jurgen garbrecht usad - ars grazinglands...
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Decade-Scale Precipitation Variationsin the Great Plains
Jurgen GarbrechtUSAD - ARS Grazinglands Research LaboratoryEl Reno, Oklahoma
USDA-ARS-GRL
Why study precipitation ?Primary climatic driver ofagriculture 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:
Annual
Decade
Century
Longer
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Monthly
Daily
- 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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Gulf of Mexico
M o u
n t a i n
sR
o c k y
GreatLakes
0 500 km
M i s s i s s i p p i
R i v e r
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2 14
56 97
8
3
C A N A D A
Gulf ofMexico
AtlanticOceanPacific
Ocean
MEXICO
aa
b
b
Increased precipitation in 1990-1999Increased precipitation in 1980-1999No increased precipitation at the end of the 20th century
11-yr MA of Annual Precipitation
Sta
nd
ard
ized
AP
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6 OK, TX, AR, LA
5S
tan
dar
diz
ed A
P
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11-yr MA of Annual PrecipitationKS, NE, MO, IO
4
Sta
nd
ard
ized
AP
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11-yr MA of Annual Precipitation
SD, MN
DryYear
WetYear
AverageYear
0
20
40
60
80P
rob
abil
ity
of O
ccu
rren
ce 1895-1979
1980-1999
33% 33% 33%
8%12%
80%
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Climate Division 5Oklahoma
Impact of the Decade-Scale Increase
in Precipitation on Stream Flow
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2 14
56 97
8
3
C A N A D A
Gulf ofMexico
AtlanticOceanPacific
Ocean
MEXICO
aa
b
b
Increased precipitation in 1990-1999Increased precipitation in 1980-1999No increased precipitation at the end of the 20th century
SDNE
KS
OK
MO
IA
WY
CO
BigBlue
Little Blue
Elkhorn
Neosho
Walnut
Verdigris
River Basin Climate DivisionState line
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River name
Drainagearea
[sq. mi.]
Periodof
record
Elkhorn, NE 6900 1929-99
Little Blue, NE 2350 1930-99Big Blue, NE 4447 1933-99
Neosho, KS 4905 1922-99
Walnut, KS 1880 1922-99
Verdigris, KS 2982 1921-99
R2 of precipitation
versusstreamflow
0.48
0.640.59
0.780.640.77
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River name
Mean annualprecipitation
Elkhorn, NE 24.0
Little Blue, NE
Big Blue, NE
Neosho, KS
Walnut, KS
Verdigris, KS
prior- 1980[in]
1980-1999[in]
26.7
27.8 30.4
27.6 29.634.6 37.8
36.2 39.937.2 40.1
Increase%
11
7 9
9
108
P
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River name
Mean annualstreamflow
Increase%
Elkhorn, NE 1098 86
Little Blue, NE 369 16Big Blue, NE 787 39
Neosho, KS 2560 36Walnut, KS 801 35Verdigris, KS 1685 35
prior- 1980[cfs]
1980-1999[cfs]2046
4281095
349410812283
Q
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Climate Divisions in Oklahoma
OKC
N
Tulsa
Little Washita River Experimental Watershed
Glover Watershed
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Great Plains Experiment Station
National WeatherService rain gage
USGS stream gage
Marlow
Anadarko
LittleWashita
Riv
er
Chickasha
N
ARS rain gage
Situation Map10 Km (6.2 mi.)
OKLAHOMA
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Little Washita River Experimental Watershed
11-yr moving average of annual runoff and precipitation depth
Ru
no f
f [m
m]
Precip
itation [m
m]
Year1950 1960 1970 1980 1990 2000
155
130
105
80
55
30
5
935
885
835
785
735
685
635
RunoffPrecipitation
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Little Washita RiverWatershed, OK
150
125
100
75
50
25
0650 700 750 800 850 900 950
Precipitation [mm]
Ru
nof
f [m
m]
11-yr moving average of annual runoff versus precipitation depth
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Little Washita RiverWatershed, OK
11-yr MA of Annual Retention vs Precipitation Depth
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Retention
Runoff
Little Washita RiverWatershed, OK
Climate Divisions in Oklahoma
OKC
N
Tulsa
Little Washita River Experimental Watershed
Glover Watershed
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Ru
no f
f [m
m]
Precip
itation [m
m]
Year1960 1970 1980 1990 2000
700
600
500
400
300
1400
1300
1200
1100
1000
RunoffPrecipitation
11-yr moving average of annual runoff and precipitation depth
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Glover Watershed, OK
Annual Precip-Runoff for Glover Watershed
300
400
500
600
700
1050 1150 1250 1350 1450
11-yr MA Precip. Broken Bow [mm]
11-y
r M
A R
un
off
de
pth
[m
m]
11-yr MA of Annual Precip-Runoff
Glover Watershed, OK
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11-yr MA of Annual Precipitation Retention Depth
500
750
1000
1250
1500
1000 1100 1200 1300 1400 150011-yr MA Precip. Broken Bow [mm]
11-y
r M
A R
ete
nti
on
De
pth
[m
m]
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Retention
Runoff
Glover Watershed, OK
Seasonal pattern of decade-scale precipitation variations
Case application using divisional precipitation data in southwestern Oklahoma
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Year
An
nu
al P
reci
p [
mm
]11-Year MA of Annual Precipitation
Southeastern Oklahoma
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-30
-20
-10
0
10
20
30
40
1895 1915 1935 1955 1975 1995Year
Dep
artu
re f
rom
me a
n %
JFMAMJ
JASOND
Annual
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11-Year MA of Seasonal PrecipitationSoutheastern Oklahoma
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
precipitation 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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ConclusionsThe decade-scale precipitation increase hashelped meet the water needs of a growing economy and society.
However, the increased demand for waterhas made the economy and society morevulnerable to decade-scale variations in precipitation.
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