Land-Climate Interactions
Chapter 2
Land energy and water balances
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
Outline: Lecture 2
Global / Land energy and water balances
Global energy balance terms
Global water balance terms
Radiative forcing, Albedo
Turbulent fluxes and feedbacks to water and heat budgets
Ground heat flux, soil temperature
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
The global energy balance
(IPCC 2007)
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
Shortwave vs longwave radiation
UV
Visible NIR
mid- and long infrared
H2O vapor is the most
important greenhouse gas.
Absorption [%]
shortwave
longwave
CO2 is the most important
anthropogenic greenhouse
gas.
CH4
N2O
O2,O3
CO2
H2O
Wavelength [μ]
Land-climate interactions, 2008
(Peixoto and Oort, 1992)
Sonia Seneviratne / IAC ETH Zurich
Global water cycle
Oceanic
Precipitation
(350%)
Oceanic
Evaporation
(390%)
Atmospheric
transport
(40%)
Terrestrial
Precipitation
(100%)
Terrestrial
Evapotranspiration
(60%)
Streamflow
(40%)
(Flux estimates: Oki and Kanae, Science 2006)
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
Global water cycle
(Oki and Kanae, Science 2006)
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
Land energy and water balances
Land energy balance
Land water balance
H2O,
CO2
SWnet
LWnet
LH=E
SH
Changes in
energy content
P
E
Soil moisture
changes
E
Rs
dS/dt
Rg
G
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
Land energy and water balances
Land energy balance
Land water
balance
Change
in energy
storage
(soil temperature, snow
melting, ..)
H2O,
CO2
SWnet
LWnet
Changes in
energy content
LH=E
SH
E
P
E
Net radiation
Latent
Sensible
= net
Soil shortwave
moisture dS/dt
heat flux heat flux
changes
- net
longwave
(also “LH”)
Rs
Ground
heat flux
Rg
G
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
Land energy and water balances
Land energy balance
Land water balance
H2O,
CO2
SWnet
LWnet
LH=E
SH
Changes in
energy content
P
Net shortwave
E
E
radiation
Soil moisture
changes
Net longwave
radiation
dS/dt
Rs
Rg
Albedo
G
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
Land energy and water balances
Land energy balance
Land water balance
Change in water storage
(soil moisture, snow, surface
water, groundwater)
H2O,
CO2
Precipitation
SWnet
LWnet
Changes in
Evapoenergy
content
transpiration
G
Land-climate interactions, 2008
LH=E
Surface
runoff
SH
Groundwater
runoff
P
E
Soil moisture
changes
E
dS/dt
Rs
Rg
Sonia Seneviratne / IAC ETH Zurich
Outline: Lecture 2
Global / Land energy and water balances
Global energy balance terms
Global water balance terms
Radiative forcing, Albedo
Turbulent fluxes and feedbacks to water and heat budgets
Ground heat flux, soil temperature
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
Spatial maps of energy balance components
• Distribution of energy balance components strongly dependent
on region / latitude
• Strong contrasts between land and ocean surfaces
Next maps: from Raschke and Ohmura (2005) and Ohmura and
Raschke (2005); In: Hantel, M. (Ed.), Landolt-Börnstein, V/6
(Geophysics/Climatology), Springer
(based on satellite measurements from International Satellite Clouds
Climatology Project (ISCCP) and reanalysis product from European
Centre for Medium-Range Weather Forecasts (ECMWF reanalysis,
ERA-40)
Annual values
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
Downward shortwave radiation
Downward shortwave radiation [W/m2]
No data
75
100
125 150 175 200
225 250 275 300
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
Net shortwave radiation
Net shortwave radiation at the ground [W/m2]
No data
Land-climate interactions, 2008
45
70
95
120
145
170
195
220 245 270
Sonia Seneviratne / IAC ETH Zurich
Downward longwave radiation
Downward longwave radiation at the ground [W/m2]
No data
135 170
205
240
275 310
345
280
415
Land-climate interactions, 2008
450
Sonia Seneviratne / IAC ETH Zurich
Net longwave radiation
Net longwave radiation at the ground [W/m2]
No data
Land-climate interactions, 2008
0
-15
-30
-45
-60 -75 -90 -105 -120 -135
Sonia Seneviratne / IAC ETH Zurich
Total net radiation
Total net radiation at the ground [W/m2]
No data
0
24
48
72
96 120 144 168 192 216
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
Sensible heat flux
Sensible heat flux [W/m2]
No data
Land-climate interactions, 2008
15
0 -15 -30 -45 -60 -75 -90 -105
Sonia Seneviratne / IAC ETH Zurich
Latent heat flux
Latent heat flux [W/m2]
No data
-25
-50 -75 -100 -125 -150 -175 -200 -225
NB:
1W/m2 1.06 mm/mth 0.035 mm/d
1mm/d 28.4 W/m2
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
Outline: Lecture 2
Global / Land energy and water balances
Global energy balance terms
Global water balance terms
Radiative forcing, Albedo
Turbulent fluxes and feedbacks to water and heat budgets
Ground heat flux, soil temperature
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
Global precipitation
1.4-2.7 mm/d
> 5.5 mm/d
4.1-5.5
mm/d
2.7-4.1
mm/d
0.7-1.4 mm/d
< 0.7 mm/d
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
Global runoff
0
0.01
0.03
0.14
0.27
0.55
1.4
2.7
5.5
13.7 [mm/d]
(Oki and Kanae, Science 2006)
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
Global soil moisture
(Dirmeyer et al., BAMS 2006)
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
Some results from the GLACE experiment
Mean of 8 AGCMs (Atmospheric Global Circulation Models), 1994 SSTs (sea surface
temperatures), JJA (June-July-August)
Observations (climatologies)
Land-climate interactions, 2008
16
16
14
14
12
12
10
10
8
8
6
6
4
4
2
2
0
0
200
180
160
140
120
100
80
60
40
20
0
200
180
160
140
120
100
80
60
40
20
0
(Seneviratne et al., JHM 2006)
Sonia Seneviratne / IAC ETH Zurich
Some results from the GLACE experiment
Mean of 8 AGCMs (Atmospheric Global Circulation Models), 1994 SSTs (sea surface
temperatures), JJA (June-July-August)
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0.5
0.4
0.3
0.2
0.1
0
-0.1
-0.2
-0.3
-0.4
-0.5
16
16
14
14
12
12
10
10
8
8
6
6
4
4
2
2
0
Land-climate interactions, 2008
0
(Seneviratne et al., JHM 2006)
Sonia Seneviratne / IAC ETH Zurich
Outline: Lecture 2
Global / Land energy and water balances
Global energy balance terms
Global water balance terms
Radiative forcing, Albedo
Turbulent fluxes and feedbacks to water and heat budgets
Ground heat flux, soil temperature
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
Radiative forcing
Greenhouse effect & Climate change
(IPCC 2007)
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
Radiative forcing
(IPCC 2007)
Examples:
Radiative forcing from greenhouse gases
Radiative forcing from albedo
Radiative forcing from aerosol
concentrations
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
Radiative forcing
NB: For land use changes, only
impacts through albedo changes are
considered here
(IPCC 2007)
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
Albedo
Albedo = Reflected portion of
downward shortwave radiation
Surface
Conditions
Albedo ()
Snow
old / fresh
0.45 / 0.85
Clouds
100 m thick
0.4
500 m thick
0.7
Ice
Oceans, Lake
0.25-0.35
Zenith angle
30o
0.05
60o
0.10
85o
0.6
Grassland
0.2-0.3
Forest
0.1-0.2
Global mean
0.3
(Dingmann 1993)
Changes in land cover (vegetation, snow, land use) can
impose a radiative forcing on climate
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
Snow/Vegetation - Albedo
Snow/Vegetation albedo feedbacks
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
Snow/Vegetation - Albedo
Old bias (March-April 1996, 850 hPa T day5 error)
For example:
Impact of representation of
vegetation/snow-albedo for
forecasts of the ECMWF
New bias (March-April 1997, 850 hPa T day5 error)
(Viterbo and Betts 1999, JGR)
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
Vegetation - climate interactions
Radiative forcing of deforestation/afforestation?
(Betts et al., Agr. For. Met. 2007)
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
Ice/snow - albedo feedback
• Strongest effect at
limit of snow/ice cover
• Also relevant for
global warming
T
• “Snowball Earth” in
past climate?
Radiation
absorbed at
surface Land-climate interactions, 2008
Snow and ice
extent ; Albedo Sonia Seneviratne / IAC ETH Zurich
Ice/snow - albedo feedback
Impact of
ice/snowalbedo
feedback for
projected
changes in
temperature
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
Albedo: Variations with spectral bands
The total albedo is not equivalent
to the albedo in the visible only:
significant fractions of shortwave
radiation in UV and NIR (NearInfrared)
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
Soil moisture - albedo feedbacks?
Albedo anomalies during the 2003 heatwave:
Constrasting feedbacks in the visible and near infrared!
Anomalies in the visible
Anomalies in the near
infrared (NIR)
Net albedo anomalies
(Teuling and Seneviratne, 2008, GRL)
NB: Combined effects of changes in vegetation and soil albedo
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
NDVI
(R. Stöckli, MeteoSwiss)
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
Satellite measurements
–spectral properties of vegetation: phenological state
– can be retrieved from satellite data (e.g. MODIS satellite)
–empirical relationships relate NDVI to biophysical parameters
like LAI (leaf area index = ratio of total leaf area to surface area;
typically between 0 for bare ground and 6 for dense forest)
Graph courtesy Wolfgang Buermann, Boston
University
NB: From NDVI, FPAR (Fraction
of Photosynthetically Active
Radiation absorbed by the green
leaves of the canopy) can be
estimated
(R. Stöckli, MeteoSwiss)
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
Phenology
• Vegetation activity has a seasonal cycle (phenology)
• Phenology is controlled by climate variables (e.g. temperature) but can also
feed back upon the climate system (e.g. summer 2003)
(Stöckli and Vidale 2004, Int. J. Remote Sensing)
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
FPAR: e.g. summer 2003
(Jolly et al., GRL 2005)
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
Outline: Lecture 2
Global / Land energy and water balances
Global energy balance terms
Global water balance terms
Radiative forcing, Albedo
Turbulent fluxes and feedbacks to water and heat budgets
Ground heat flux, soil temperature
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
Land energy and water balances
Land energy balance
Land water balance
H2O,
CO2
SWnet
LWnet
LH=E
Changes in
energy content
SH
P
E
Soil moisture
changes
E
Rs
dS/dt
Rg
G
The partitioning of the net incoming energy (net radiation)
in the latent and sensible heat fluxes is controlled by soil
moisture if it is the limiting factor for evapotranspiration
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
The concept of limiting factors for evapotranspiration
(Nemani et al., Science 2003)
(Based on modelling and observational estimates; slight variations are possible
depending on chosen product / model)
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
Bowen ratio
Bowen ratio: Ratio between sensible und latent heat fluxes:
B =
SH
LH
=>
B << 1 moist surface, LH dominates over SH
=>
B >> 1 dry surface, SH dominates over LH
Low Bowen ratio
High Bowen ratio
[For more details, see lecture 4]
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
Effects for recent heatwaves
Number of hot
days (> 90%ile)
Observations
Reference
simulations
With soil
moisture
climatology
(Fischer et al. 2007, GRL)
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
Land-atmosphere coupling: Role of vegetation
Impact of vegetation cover for surface exchanges during the 2003
heatwave
August 1, 2000
August 10, 2003
crops and
pastures
NDVI:
active
vegetation
NDVI:
-0.35
IR:
soil
temperature
NDVI:
-0.00
forest
Aster Satellite
(NASA/Japan)
+20 ºC
+11 ºC
500 m
27 ºC
42 ºC
5x5 km view
in Central France
500 m
32 ºC
47 ºC
Land-climate interactions, 2008
(Zaitchik et al. 2006, Int. J. Clim.)
Sonia Seneviratne / IAC ETH Zurich
Role of soil moisture for climate-change projections
Impact on summer temperature variability in Europe (present / future)
Standard deviation of summer (JJA) temperature, simulations with CHRM regional climate model
CTL (1970-1989)
SCEN (2080-2099)
Impact on
occurrence of
heatwaves!
CTLUNCOUPLED
(Schär et al. 2004, Nature)
Land-climate interactions, 2008
SCENUNCOUPLED (2080-2099)
No interannual
variations of
soil moisture
(Seneviratne et al. 2006,
Nature)
Sonia Seneviratne / IAC ETH Zurich
Role of soil moisture for To variability
Soil moisture [mm]
Seasonal Cycle of Soil Moisture
no limitation
on evapotranspiration
wet climate
CTL (1961-1990)
SCEN (2071-2100)
transitional
climate
Month
Threshold for soil
moisture limitation on
evapotranspiration
close to plant wilting
point in all years
dry climate
Absolute threshold
for evapotranspiration (plant
wilting point)
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
Land-atmosphere coupling and climate change
percentage of To variance
explained by coupling [%]
T2 (COUPLED ) T2 (UNCOUPLED )
T2 (COUPLED )
land-atmosphere coupling
strength parameter
analogous to GLACE
• Shift of region of strong soil moisture-To coupling from the Mediterranean to most of
Central and Eastern Europe in future climate more future heatwaves in this region
(Seneviratne et al. 2006, Nature)
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
Comparison with IPCC AR4 GCMs
Indirect measure of coupling between soil moisture & To:
Correlation between summer evapotranspiration and
temperature (ET,T2M)
Negative correlation: strong soil moisturetemperature coupling (high temperature as
result of low/no evapotranspiration)
Positive correlation: low soil moisturetemperature coupling (high temperature
leads to high evapotranspiration)
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
Comparison IPCC AR4 GCMs: (ET,T2M)
CTL time period
SCEN time period
Climate-change signal
RCM
3 “best”
GCMs
All
GCMs
(Seneviratne et al. 2006, Nature)
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
Summary
• The projected enhancement of To variability in Central
and Eastern Europe is mostly due to changes in landatmosphere coupling
• Climate change creates a new hot spot of soil moisture To coupling in Central and Eastern Europe in the future
climate (shift of climate regimes)
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
Outline: Lecture 2
Global / Land energy and water balances
Global energy balance terms
Global water balance terms
Radiative forcing, Albedo
Turbulent fluxes and feedbacks to water and heat budgets
Ground heat flux, soil temperature
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
Ground heat flux, soil temperature
• Ground heat flux is often a negligible term of the energy
balance (averaged over one day, averaged over one year)
• Can be nonetheless important in some situations: soil
temperature memory, permafrost; also indicative of soil
properties (soil physical properties, soil moisture content may be used as indirect measurement)
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
Vertical heat conduction in soils
Combine with Fourier’s law:
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
Thermal properties of soil constituents and soils
(Hillel 1998)
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
Diurnal and seasonal cycle of soil temperature
(see also Hillel 1998,
Chap. 12)
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
Snow and soil temperature
(Bonan 2002)
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
Outline: Lecture 2
Global / Land energy and water balances
Global energy balance terms
Global water balance terms
Radiative forcing, Albedo
Turbulent fluxes and feedbacks to water and heat budgets
Soil temperature, ground heat flux
Quiz
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich
Vegetation-climate interactions
(Serengeti, Tanzania)
Land-climate interactions, 2008
Sonia Seneviratne / IAC ETH Zurich