evolving issues in land surface hydrology at continental to global scales dennis p. lettenmaier...
TRANSCRIPT
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Evolving issues in land surface hydrology at continental to global
scalesDennis P. Lettenmaier
Department of Civil and Environmental Engineering
University of Washington
for presentation at
Department of Atmospheric SciencesClouds and Precipitation Seminar
November 2, 2006
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Outline this talk
• Motivation for this talk – potential synergisms across campus?
• Macroscale hydrology modeling construct• U.S. Drought reconstruction• North American Monsoon• Western U.S. snowpack and runoff trends• Anthropogenic impacts on continental surface
water fluxes• Applications:
– Westwide forecast system– Climate impact assessment
• Challenges to the field
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Macroscale hydrology modeling construct
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Investigation of forest canopy effects on snow accumulation and melt
Measurement of Canopy Processes via two 25 m2 weighing lysimeters (shown here) and additional lysimeters in an adjacent clear-cut.
Direct measurement of snow interception
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0
50
100
150
200
250
300
350
11/1/96 12/1/96 1/1/97 2/1/97 3/1/97 4/1/97 5/1/97
SW
E (
mm
)ObservedPredicted
Below-canopy
Shelterwood
Tmin = 0.4 C Zo shelterwood = 7 mmTmax = 0.5 C Zo below-canopy = 20 cm
Albedo based onexponential decaywith age; fitted tospot observationsof albedo
Calibration of an energy balance model of canopy effects on snow accumulation and melt to the weighing lysimeter data. (Model was tested against two additional years of data)
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Summer 1994 - Mean Diurnal Cycle
Point Evaluation of a Surface Hydrology Model for BOREAS
Flu
x (W
/m2)
-100
100
300 Rnet
-50
50
150
250
H
0
60
120LE
0 3 6 9 12 15 18 21 24
SSA Mature Black Spruce
Rnet
H
LE
0 3 6 9 12 15 18 21 24
SSA Mature Jack Pine
Rnet
H
LE
0 3 6 9 12 15 18 21 24
Local time (hours)
NSA Mature Black Spruce
Observed Fluxes
Simulated Fluxes
Rnet Net Radiation
H Sensible Heat Flux
LE Latent Heat Flux
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Range in Snow Cover ExtentObserved and Simulated
Eurasia North America
J F M A M J J A S O N D JMonth
Observed Simulated
0
4
8
12
16
20
sno
w c
ove
r ex
ten
t (1
06 km
2 )
J F M A M J J A S O N D JMonth
0
2
4
6
8
10
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June 18th-July 20th, 1997
UPPER LAYER SOIL MOISTURE
0.40
0.10
0.20
0.30
SO
IL M
OIS
TU
RE
(%
)
XX
X
X
XX
X
XX
X
XX
XX X
X
TOPLATS regionalESTAR distributed
TOPLATS distributed
11:00 CST JULY 12 1997
ESTAR TOPLATS
50
10
ESTAR TOPLATS
10
50
11:00 CST JUNE 20, 1997
Illinois soil moisture comparison
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Cold Season Parameterization -- Frozen Soils
Key
Observed
Simulated
5-100 cm layer
0-5 cm layer
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Macroscale modeling approach (“top down”)
1 Northwest 5 Rio Grande 10 Upper Mississippi2 California 6 Missouri 11 Lower Mississippi3 Great Basin 7 Arkansas-Red 12 Ohio4 Colorado 8 Gulf 13 East Coast
9 Great Lakes
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U.S. Drought Reconstruction (1916-2003)
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Key aspects of the approach
• Spatially and temporally continuous dataset of hydro-climatological variables (one-half degree lat-long, daily)
• Drought event identification using spatio-temporal clustering
• Severity estimated for each drought event for different durations and spatial extents
• Results used to construct Severity-Area-Duration (SAD) curves
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Defining drought extent
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Evolution of droughts over time
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U.S. drought history (1915-2003)
• Droughts of 1930s and 1950s most intense and longest respectively (also, largest spatial extent)
• 2000s western U.S. drought among the worse droughts
• Long dry spells during the 2000s drought hindered recovery in terms of runoff
• Other significant droughts included 1988, 1977 (W U.S.), mid-1960s (NE U.S.)
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Model Runoff Annual Trends
• 1925-2003 period selected to account for model initialization effects
• Positive trends dominate (~28% of model domain vs ~1% negative trends)
Positive +
Negative
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HCN Streamflow Trends• Trend direction and significance in streamflow
data from HCN have general agreement with model-based trends
Subset of stations was used (period 1925-2003)
Positive (Negative) trend at 109 (19) stations
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Soil Moisture Annual Trends
• Positive trends for ~45% of CONUS (1482 grid cells)
• Negative trends for ~3% of model domain (99 grid cells)
Positive +
Negative
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Trends in soil moisture drought duration
Severe Drought (10%) Extreme Drought (20%)
Intense Drought (30%) Moderate Drought (40%)
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Soil Moisture Drought Spatial Extent
Severe Drought (10%)
Extreme Drought (20%)
Intense Drought (30%)
Trend for the drought spatial extent is negative (95% significance) for all threshold levels (10-50%)
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Soil Moisture Drought Intensity● Droughts events identified using spatio-
temporal clustering and threshold of 20th percentile
● Intensity time series constructed from the maximum average intensity
• Mann-Kendall test for trend showed a statistically significant (98%) upward trend in “individual event” drought intensity
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North American Monsoon teleconnection analysis
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North American Monsoon System (NAMS)
North American monsoon is experienced as a pronounced increase in rainfall from extremely dry May to rainy June.
North American Monsoon Experiment (NAME): Tier 1,2,3. (http://www.cpc.ncep.noaa.gov/products/precip/monsoon/NAME.html)( Comrie & Glenn, 1998 )
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The NAMS concept --- thermal contrast between land and adjacent
oceanic regions
( http://www.ifm.uni-kiel.de )
Question: how is the strength of the monsoon (in terms of precipitation) related to antecedent land surface conditions?
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Winter Precipitation - Monsoon Rainfall feedback hypothesis
Higher (lower) winter precipitation & spring snowpack
More (less) spring & early summer soil moisture
Weak (strong) monsoon Lower (higher) spring & early summer surface temperature
Possible mechanism:
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Winter Precipitation – Monsoon Onset
15-year Moving Average Correlation of PI versus monsoon onset
Correlation of JFM Precip and Monsoon Onset Date
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Late
Early
Late Early
JFM Precipitation in extreme monsoon years
May Soil moisture in extreme monsoon years
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May Sm in extreme monsoon years
May Ts in extreme monsoon years
Late Early
Late Early
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Correlation:May first layer Sm & May Ts
Correlation:May Ts & monsoon onset
May soil moisture plays some role in pre-monsoon seasonal surface thermal condition
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Western U.S. snowpack trend analysis
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1916-2003
Trend %/yr
DJF
avg
T (
C)
1925-1946with1977-2003
Trend %/yr
DJF
avg
T (
C)
DJF
avg
T (
C)
1947-2003
Decadal Variability Doesn’t Explain the Temperature Related Effects to Snowpack
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b) Max Accum. c) 90 % Melt a) 10 % Accum.
DJF
Tem
p (C
)
Change in Date
Change in Date
DJF
Tem
p (C
)
Change in Date
Change in Date
DJF
Tem
p (C
)
Change in Date
Change in Date
Trends in the Date of Snow Accumulation and Melt
1916-2003
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Anthropogenic impacts on continental surface water fluxes
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Introduction - Outline
• Background– Irrigation:
• 60-70 % of global water withdrawals (Shiklomanov, 1996, 1997)
– Reservoirs (ICOLD): • 35 % of large dams built for
irrigation purpose alone– Freshwater scarcity: one of the most
important environmental issues of the 21st century (UNEP, 1999)
• Approach– VIC macroscale hydrologic model
• Irrigation scheme• Reservoir model
• Results• Conclusions• Future research
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Irrigated areas
Siebert, S., Döll, P., Hoogeveen, J., 2002. Global map of irrigated areas version 2.1, Center for Environmental Systems
Research, University of Kassel, Germany/Food and Agriculture Organization of the United Nations, Rome, Italy
•Irrigated areas, globally: • 2.5*106 km2
• 1.7 % of global land area
•Location of irrigated areas:• Asia: 68 %• America: 16%• India, China, USA: 47 %
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Irrigation water requirements
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Reservoirs
Main purpose of dam
Irrigation
Flood
Hydro
Fishing
Navigation
Recreation
Water supply
Unknown
ICOLD, 2003. World Register of Dams 2003, International Commission on Large Dams (ICOLD), Paris, France.
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Model development: Reservoir model
365365 365
1min1
1
max
,
min
idaydayres
iday idaydayinendi
iini
EQQSS
QS
Qi
107min QQi
RiverNon-irrigated part of grid cellIrrigated part of grid cellReservoirDamWater withdrawal pointWater withdrawn from local riverWater withdrawn from reservoir
1st priority: Irrigation water demand 2nd priority: Flood control3rd priority: Hydropower production
If no flood, no hydropower: Make streamflow as constant as possible
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Reservoir model
1st priority: Irrigation water demand 2nd priority: Flood control3rd priority: Hydropower production
If no flood, no hydropower: Make streamflow as constant as possible
Reservoir evaporation: Penman
Model evaluation: 1) Columbia, 2) Colorado, and 3) Missouri River basins
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Results: Runoff and evapotranspiration
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Results: Evapotranspiration
a) Effects of cropland expansion (1992 – 1700)
b) Effects of cropland expansion and irrigation (1992 – 1700)
c) Effects of irrigation (1992 - 1992)
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Results: Streamflow
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Colorado River basin
•Irrigation included:•Q: 26.5 mm year-1
•ET: 350 mm year-1
•Naturalized:•Q: 42.3 mm year-1
•ET: 335 mm year-1
Irrigation water
requirements
Evapotranspiration
increase
Changes in sensible heat
fluxes
Changes in surface
temperatures
Changes in latent heat
fluxes
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Applications: Westwide hydrologic forecast system
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UW Forecast Approach Schematic
NCDC COOP station obs.
up to 3 months from
current
local scale (1/8 degree) weather inputs
soil moisturesnowpack
VIC Hydrologic model spin up
SNOTEL
Update
streamflow, soil moisture, snow water equivalent, runoff
25th Day, Month 01-2 years back
index stn. real-time
met. forcings for spin-up
gap
Hydrologic forecast simulation
Month 12
INITIAL STATE
ObservedSWE
Assimilation
ensemble forecasts ESP traces CPC-based outlook NCEP CFS ensemble NSIPP-1 ensemble
West-wide System
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West-wide System
www.hydro.washington.edu/forecast/westwide/
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Application: Colorado River basin climate impact assessment
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Water Resource Metrics
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
A2 Avg.Shortfall
B1 Avg.Shortfall
A2 % of NOSHTG
B1 % of NOSHTG
A2 % ofSHTG 3
B1 % ofSHTG 3
BC
M/y
r
/
Pro
bab
ilit
y
BASE
2010-2039
2040-2069
2070-2099
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Challenges
• Role of new observation methods
• Scaling and the physically based model paradigm
• Understanding the sensitivity of runoff to long-term dec-cen climate variability and change