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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