7 Eric Small drought presentation - Sahraweb.sahra.arizona.edu/.../7_Eric_Small.pdf · Microsoft...
Transcript of 7 Eric Small drought presentation - Sahraweb.sahra.arizona.edu/.../7_Eric_Small.pdf · Microsoft...
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SAHRASAHRA
Drought, vegetation, and water cyclingin the semiarid southwest
Eric SmallUniversity of Colorado [email protected]
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s
Soil
Sediment/Rock
Precipitation~250 mm/yr
Runoff? mm/yr
Evapotranspiration(ET) ~250 mm/yr
Recharge? mm/yr
Vegetation plays a key role in water cycling
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July-August1999
July-August1995
Dry WetVariability of rainfall
August 1999 August 1995
Vegetation responds to rainfall variability
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1950’s drought
Annual Precipitation: Central New Mexico
100
200
300
1900 1920 1940 1960 1980 2000
Year
Pre
cip
itat
ion
(mm
)
How does vegetation response to drought influence water cycling?
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Shrub invasion in the southwest:Was drought important?
Early 1800’s: Black Grama Today: Creosotebush
1 m
Vegetation response to drought:Depends on plant type
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Invasion of woody species into grassland
1964
1903 Southern Arizona
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•Soil erosion•Nutrient availability in soil•hydrology
Environmental impacts of shrub invasion
Runoff in shrubland and grassland
Time (min)
5
10
15
00 20 40 60
Shrubland
Grassland
Dis
char
ge(c
m3
s-1m
-2)
Abrahams et al. 1995
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Annual Precipitation: Central New Mexico
100
200
300
1900 1920 1940 1960 1980 2000
Year
Pre
cip
itat
ion
(mm
)
“1950’s drought”
Shrubs more drought resistant
•Deeper roots
•Able to grow in dryer soil
•Grow throughout the year
Untangle multiple factorsdrought & land use
Shrubs favored under grazing
•Livestock prefers grass
•Grazing reduces fire
•Nutrient and soils modified
1800’s: 5 million sheep1900’s: > 2 million cattle
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SAHRASAHRA
Large scale field experimentsto study drought impacts
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Shrubland: 28% Canopy Grassland: 54% canopy3 meters
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Shrubland Grassland3 meters
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Annual Precipitation: Central New Mexico
100
200
300
1900 1920 1940 1960 1980 2000
Year
Pre
cip
itat
ion
(mm
)
1950’s drought
How does climatic change or variability influence water cycling and ecosystems?
-3
-2
-1
0
1
2
3
0 500 1000 1500 2000
Year
Rec
on
stru
cted
Pre
cip
itat
ion
(sta
nd
ard
dev
iati
on
s)
Grissino-Mayer, 1995
-3
-2
-1
0
1
2
3
0 500 1000 1500 2000
Year
Rec
on
stru
cted
Pre
cip
itat
ion
(sta
nd
ard
dev
iati
on
s)
Grissino-Mayer, 1995
How does precipitation amount influence critical zoneprocesses in desert grassland and shrubland?
•Does ecosystem response influence water cycling at basin scale?
•Are water-plant-soil interactions important?
•Does drought lead to shrub invasion?
Sevilleta LTER
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Model of drought response in grassland
Grassland
Decreased productivityHigh mortality
More evaporationLess transpiration
Less infiltrationMore heterogenous
Less CanopyMore bare soil
Connected drainage networkMore runoff
Soil erosion andNutrient redistribution