Land surface processes in the global energy and water cycles Part II: Processes, Interactions, Feedbacks 3

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Land-Atmosphere-Climate Interactions

(Winter Term 2006/2007)

Sonia I. Seneviratne and Christoph Schär Institute for Atmospheric and Climate Science

Universitätsstrasse 16, 8092 Zurich

sonia.seneviratne@env.ethz.ch schaer@env.ethz.ch

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Part I: Basics 1. Introduction

2. Land surface processes in the global energy and water cycles Part II: Processes, Interactions, Feedbacks

3. Feedback processes, Threshold effects 3.1. Soil moisture - climate interactions 3.2. Vegetation - climate interactions

3.3. Snow - climate interactions Part III: Modeling

4. Modeling of the coupled land-atmosphere system 4.1. Climate models and their components

4.2. Convective parameterizations, boundary layer models 4.3. Land surface models

Part IV: Outlook, current research questions

Outline

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24.10.2006 SIS 1. Introduction

31.10.2006 CS 2. Land surface processes in the global energy and water cycles (a) 07.11.2006 SIS 2. Land surface processes in the global energy and water cycles (b) 14.11.2006 CS 2. Land surface processes in the global energy and water cycles (c) 21.11.2006 Reserve date (Hydrologie-Seminar, ENSEMBLES)

28.11.2006 EJ Discussion of Exercises (1)

05.12.2006 SIS 3. Feedback processes, threshold effects (a) 12.12.2006 Reserve date (AGU)

19.12.2006 SIS 3. Feedback processes, threshold effects (b) 09.01.2007 EJ Discussion of Exercises (2)

16.01.2007 CS 4. Modeling of the coupled land-atmosphere system (a) 23.01.2007 SIS 4. Modeling of the coupled land-atmosphere system (b) 30.01.2007 SIS 5. Outlook, current research questions

SIS = Sonia I. Seneviratne, CS = Christoph Schär, EJ = Eric Jäger

Schedule

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1/2-day excursion at the FLUXNET/CARBOEUROPE sites of Lägeren and/or Oensingen + Web-FACE experiment in Hofstetten near Basel Please register if interested!

Excursion

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Total credit points: 3

Exam: 30mn, oral

(after the end of the course)

Exercises: Distribution Discussion Due on

1 14.11.2006 28.11.2006 05.12.2006

2 19.12.2006 09.01.2007 16.01.2007

Contact: Eric Jäger, eric.jaeger@env.ethz.ch

Credit points / exam, exercises

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• Material

– Copies of most slides of the course – Definitions, equations, figures, ...

– No full text

– Documents the lecture

– No substitution for attending the lecture

• Distribution – At each lecture

– Contribution to costs: 10 CHF (for all parts)

• Web site

– Exercises (1+2) and example solutions will be available on a web site – Linked from http://www.iac.ethz.ch/staff/sonia/lecture

Course material

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Kabat et al. 2004 (eds.): Vegetation, Water, Humans and the Climate. Springer, Berlin, 566pp., ca 140!

Global climate

Hartmann, D.L., 1994: Global Physical Climatology. Academic Press, 408pp., ca. 80€

Peixoto, J.P., and A.H. Oort, 1992: Physics of Climate. Amer. Inst. of Physics, 520pp., ca. 75 ! Ruddimann, W.F., 2001: Earth‘s Climate - Past and Future. W.H. Freeman and Company, 465pp., ca. 85 !

Hydrology

Brutsaert, W., 2005: Hydrology - An Introduction. Cambridge University Press, 605pp., ca. 62 !

Soil physics

Hillel, D., 2004: Introduction to Environmental Soil Physics. Elsevier, 494pp., ca. 63!

Hillel, D., 1998: Environmental Soil Physics: Fundamentals, Applications, and Environmental Considerations. Academic Press, 771pp., ca. 80 !

Recommended literature

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Land-Atmosphere-Climate Interactions

Chapter 1 Introduction

Sonia I. Seneviratne and Christoph Schär, Institute for Atmospheric und Climate Science, ETH Zürich Winter term 2006/2007

Outline 10

• Why study land-atmosphere interactions?

• Land as storage component for energy and water

• Overview of the land energy and water balances

• Example of some relevant feedbacks and interactions

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The climate system 11

(PIK)

Land-atmosphere interactions 12

Energy

Water

• We consider in this lecture interactions linked with exchanges of energy, water, and to a lesser extent CO₂

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Land-atmosphere interactions 13

Energy

Water

• We consider in this lecture interactions linked with exchanges of energy, water, and to a lesser extent CO₂

! mostly physical aspects

•Does not include full biogeochemical cycle (e.g. CH₄, nitrogen cycle, etc...)

Why study land-atmosphere interactions? 14

• relevant for climate variability and extreme events (droughts, heatwaves, heavy precipitations events, floods, ...)

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• relevant for numerical weather prediction, seasonal forecasting, climate change projections ...

• important source of uncertainty for our understanding of the climate system due to lack of observations and complexity (feedbacks, heterogeneity)

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Outline 17

• Land energy and water balances

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• 2/3 of the Earth surface are covered with oceans, and thus the impact of oceans on climate often received more attention in past research:

• heat storage and transport in the oceans (gulf stream, El Niño)

• “memory”: impact on mid- to long- term climate variability (seasonal forecasting)

• Storage of water on land plays a similar role!

Land as storage component for energy & water

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Land vs. Oceans 19

ATMOSPHERE

LAND OCEANS

Role of land-atmosphere coupling vs ocean-atmosphere coupling for climate variability

energy, water, CO₂

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ATMOSPHERE

Oceans act mostly as heat storage

OCEANS

Land vs. Oceans

LAND

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ATMOSPHERE

LAND Land areas

act mostly as water

storage

Oceans act mostly as heat storage

OCEANS

Land vs. Oceans

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ATMOSPHERE

LAND OCEANS

Liquid Water Water vapour

~ 2.45 J kg^-1(at 20^oC)

NB: Water storage is also an indirect heat storage!

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Latent heat of vaporization

Comparison with specific heat of water (at 0^oC):

=> Evaporation uses the same amount of energy as a warming of ~590^oC !!

Phase changes

L = 2.5 10⁶ J kg^-1 at 0^oC L = 2.26 10⁶ J kg^-1 at 100^oC

c_p = 4.22 10³ J kg^-1 K^-1 at 0^oC

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For the warming from ice (0ºC) to water vapour (100ºC):

• 86% of the energy input is used for phase changes

• and only 14% for the warming itself!

Energy input

Temperature !E=L_w-d

!E=c_p,ice·!T

!E=L_e-w

Liquid water and water vapour

Liquid water

!E=cp,liquid water·!T

Water vapour

Ice and water Ice

Energy used for warming/phase changes

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For the warming from ice (0ºC) to water vapour (100ºC):

• 86% of the energy input is used for phase changes

• and only 14% for the warming itself!

Energy input

Temperature !E=L_w-d

!E=c_p,ice·!T

!E=L_e-w

Energy used for warming/phase changes

Liquid water and water vapour

Liquid water

!E=cp,liquid water·!T

Water vapour

Ice and water Ice

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ATMOSPHERE

LAND OCEANS

~ 2.45 J kg^-1(at 20^oC)

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ATMOSPHERE

LAND OCEANS

~ 2.45 J kg^-1(at 20^oC)

“negative heat” storage

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ATMOSPHERE

LAND OCEANS

Moreover: Also snow and ice storage are relevant for climate

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• can both damp and enhance climate variability (see later)

• “memory”: relevant for seasonal forecasting in particular in the mid- latitudes

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Outline 31

• Overview of land energy and water balances

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dH_s/dt

H₂O, CO₂

SW_net LW_net LH="E SH P E R_s

R_g

dS/dt

G

Land energy balance Land water balance

E

Land energy and water balances

dS/dt

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dH_s/dt

H₂O, CO₂

R_g

dS/dt

G

E

dS/dt

!

"H_s

"t = R* –SH –LH –G

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dH_s/dt

H₂O, CO₂

R_g

dS/dt

G

E

dS/dt

!

"H_s

"t = R* –SH –LH –G

Change in energy storage (soil temperature, snow melting, ..)

Net radiation

= net shortwave - net longwave

Sensible heat flux

Latent heat flux

Ground heat flux

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dH_s/dt

H₂O, CO₂

R_g

dS/dt

G

E

dS/dt

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dH_s/dt

H₂O, CO₂

R_g

dS/dt

G

E

dS/dt

Change in water storage (soil moisture, snow, surface water, groundwater)

Precipitation Evapo- transpiration

Surface runoff

Ground- water runoff

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dH_s/dt

H₂O, CO₂

R_g

dS/dt

G

E

The land energy and water balances are coupled through the latent heat flux/evapotranspiration!

Land energy balance Land water balance dS/dt

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dH_s/dt

H₂O, CO₂

R_g

dS/dt

G

E

dS/dt

The partitioning of the net radiation in the latent and sensible heat fluxes is controlled by the availability of soil moisture

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dH_s/dt

H₂O, CO₂

R_g

dS/dt

G

E

dS/dt

Important vegetation control on evapotranspiration: e.g.

dependent on plant type, atmospheric CO₂ concentration, …

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dH_s/dt

H₂O, CO₂

R_g

dS/dt

G

E

dS/dt Complex interactions between evapotranspiration and precipitation (boundary-layer processes)

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dH_s/dt

H₂O, CO₂

R_g

dS/dt

G

E

dS/dt

Land energy balance Land water balance Clouds and water vapour also

impact the energy cycle

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dH_s/dt

H₂O, CO₂

R_g

dS/dt

G

E

dS/dt

SW_net= SW_in (1 - # ) Albedo # is dependent on snow and vegetation cover

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Summary:

• The processes involved in the land energy and water balances are tightly coupled:

– soil moisture and vegetation control the partitioning of incoming energy in the sensible and latent heat fluxes

– clouds, water vapour are coupled with surface processes

– vegetation and snow albedo impact the radiation fluxes directly

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Summary:

• The processes involved in the land energy and water balances are tightly coupled:

– soil moisture and vegetation control the partitioning of incoming energy in the sensible and latent heat fluxes

– clouds, water vapour are coupled with surface processes

– vegetation and snow albedo impact the radiation fluxes directly

• High complexity of the system!! (feedbacks and interactions)

• Importance of vegetation and soil processes means added issue of heterogeneity (soil types, land use, vegetation cover/trees)

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Outline 45

• Overview of land energy and water balances

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[ºC] [%]

Soil moisture and future summer heatwaves

(Schär et al. 2004, Nature)

$%/%

$T

Changes in summer (JJA) temperature characteristics

Changes in T^o

variability are likely to be as important (or more important) than changes in the mean

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• Land surface processes?

• Circulation patterns?

What are the responsible processes?

(Meehl and Tebaldi 2004, Science)

500 hPa: A1B-present 3-day worst heat event daily T^o: A1B-present

Month

Soil moisture [mm]

Seasonal Cycle of Soil Moisture

(Vidale et al. 2006)

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Standard deviation of the summer (JJA) 2-m temperature

(Seneviratne et al. 2006, Nature, 443, 205-209)

SCEN CTL

CTL_UNCOUPLED SCEN_UNCOUPLED

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Standard deviation of the summer (JJA) 2-m temperature

SCEN CTL

CTL_UNCOUPLED SCEN_UNCOUPLED

Most of the enhancement of summer temperature variability in SCEN disappears in the SCEN_UNCOUPLED simulation

(Seneviratne et al. 2006, Nature, 443, 205-209)

Energy balance: Forests vs. Pastures 50

(Zaitchik et al. 2006, Int. J. Clim.) Aster Satellite

(NASA/Japan) 5x5 km view in Central France

NDVI:

active vegetation

IR:

soil temperature

32 ºC 47 ºC

500 m

August 10, 2003

+11 ºC +20 ºC

NDVI:

-0.00 NDVI:

-0.35

27 ºC 42 ºC

500 m

August 1, 2000

crops and pastures

forest

Summer 2003: Vegetation cover relevant for energy balance!

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Phenology 51

• 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)

Soil moisture - precipitation feedback 52

(Beljaars et al. 1996, MWR)

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Soil moisture - precipitation feedback 53

(Schär et al. 1999, J. Climate)

Snow/Vegetation - Albedo 54

(Viterbo and Betts 1999, JGR)

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Land-atmosphere coupling and climate change 55

land-atmosphere coupling strength parameter analogous to GLACE

• Shift of region of strong soil moisture-T^o coupling from the Mediterranean to most of Central and Eastern Europe in future climate ! more future heatwaves in this region

!

"T(COUPLED)

2 #"T

2 (UNCOUPLED)

"T(COUPLED)

2

percentage of T^o variance explained by coupling [%]

(Seneviratne et al. 2006, Nature, 443, 205-209)

Summary 56

• Land-atmosphere interactions are a key aspect of the climate system:

– Relevant for climate variability and extreme events

– Important for numerical weather prediction, seasonal forecasting – Affected by global warming AND key player of climate change

• Important link between the energy and water cycles

• Memory component of the climate system (storage)

• High complexity due to range of involved feedbacks and interactions, as well as spatial heterogeneity