EcohydrologyPhilippe CHOLERphilippe.choler@ujf-grenoble.frwww.philippe-choler.comStaff scientist at CNRS(University of Grenoble - France)

Outline of the lecturesLecture 1• 1. What is ecohydrology ?• 2. The "green" water flow in the global water cycle

Reading Discussion : Jung, M., et al. 2010. Recent decline in the global land evapotranspiration trend due to limited moisture supply. - Nature 467: 951-954.

Lecture 2• 3. The soil water balance• 4. Processes and models of dryland dynamics

Reading Discussion : Good, S. P. and Caylor, K. K. 2011. Climatological determinants of woody cover in Africa. - Proc. Natl. Acad. Sci. USA 108: 4902-4907..

Lecture 3• 4. Processes and models of dryland dynamics (continued)• 4. Ecology of snow-covered ecosystems

1. What is ecohydrology ?

Fundamentals of Ecohydrology (Philippe CHOLER – CNRS – France). Wuwei (09/2013)

Water is life

Fundamentals of Ecohydrology (Philippe CHOLER – CNRS – France). Wuwei (09/2013) Source : http://www.hpcf.upr.edu/~abel/phl/Liquid_Water.jpg

The habitable zone (HZ)

Fundamentals of Ecohydrology (Philippe CHOLER – CNRS – France). Wuwei (09/2013) Source : https://www.e-education.psu.edu/astro801/content/l12_p4.html

Water phase diagram

Point critique374°C - 219 atm

Enthalpies de changement d'état:Fusion 6kJ mol-1Ebullition 40.7 kJ mol-1Enthalpies de changement d'état:Fusion 6kJ mol-1Vaporisation 40.7 kJ mol-1

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25°C, 80% RH, pw ≈ 2530 Pa

5°C, 20% RH, pw ≈ 174 Pa

solidprecipitation

liquidprecipitation

Dependence of the HZ to atmospheric effects

Fundamentals of Ecohydrology (Philippe CHOLER – CNRS – France). Wuwei (09/2013) Source: Vladilo G., et al. (2013) Astrophysical Journal, 767.

Habitability (h) : mean fraction of the planet’s surface on which

liquid water could exist.

Fundamentals of Ecohydrology (Philippe CHOLER – CNRS – France). Wuwei (09/2013)

The water balance

Fundamentals of Ecohydrology (Philippe CHOLER – CNRS – France). Wuwei (09/2013)

Evapo-Transpiration (ET)

Precipitation –Rainfalls (P)

Surface (R1) & Subsurface (R2) Runoff -

Ruissellement (R)

Groundwater

Bassin versant –Watershed – river basin

Partitioning 1Runoff vs. Soil infiltration

Partitioning 2Evapotranspiration vs. groundwater recharge

vapo

r

Streamflowtemporally lagged, spatial integral of

runoff over a river basin

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"Blue"water

"Green" water

R2

R1

Blue and green water (FAO, 1995, 1997)

• Blue water flow is the visible liquid water flow moving above and below the ground as surface or sub-surface runoff, respectively

• Green water flow is the invisible flow of vapour to the atmosphere

Fundamentals of Ecohydrology (Philippe CHOLER – CNRS – France). Wuwei (09/2013) Source: Falkenmark M. & Rockstrom J. (2004). Earthscan.

Coupling between water and energy balance

Rayonnem

ent net

Apport d'énergie

Principe de conservation de l'énergie (valeurs moyennes sur une période t)

Flux de chaleur Latente (HL )

(Latent Heat Flux)

Flux de chaleur Sensible (H)

(Sensible Heat Flux)

Pertes d'énergie

Flux radiatif net(RN)

(Net Radiation)

Flux de chaleur dans le sol (HG)

(Ground Heat Flux)

RN = H + HL + HG

Ta

Ts

HL = ETET évapotranspiration : en kg m-2 s-1 d’eau échangée : chaleur latente de vaporisation de l'eau (latent heat of vaporization of water).

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"Green" water

radiation

convection

conduction

Example of daily time course of fluxes

(d'après Long & al 1964)

Flux d’énergie échangés au-dessus d'un champ d'avoine (énergie par unité de temps et de surface)

Le jour, une très large part de l’énergie incidente est utilisée pour l’évapotranspiration

(J s

-1m

-2)

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Stomatal control of leaf water and carbon fluxes

Phénomènes diffusifs régis par la loi de Fick

Transpiration (T)

T = gtot,H2O (ei - ea)/Patm

ex pression partielle de vapeur d'eau (chambre sous-stomatique, surface foliaire, atmosphère)

gtot,H20 : conductance stomatique à la vapeur d'eau

Assimilation nette (An)

An = gtot,CO2 (Ca - Ci)/Patm

Cx pression partielle de CO2 (chambre sous-stomatique, surface foliaire, atmosphère)

gCO2 conductance stomatique au CO2

Ci

CO2 H2Oea

Cs

Ca

couchelimite

es

ei

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Coupling between water and carbon cycles

A perfect anti-correlation betweenmeasurements of CO2 and water vapor concentration is predicted if exchanges are only controlled by stomata(Monin-Obukhov Similarity Theory)

WUE : Water Use Efficiency = An / T

Source: Scanlon T.M. & Kustas W.P. (2010) Agricultural and Forest Meteorology, 150, 89-99.

CO2

H2O

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Coupling between soil moisture and precipitation

Fundamentals of Ecohydrology (Philippe CHOLER – CNRS – France). Wuwei (09/2013) Source: Koster R.D., et al. (2004) Science, 305, 1138-1140.

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Plant responses to precipitation in semi-arid grasslands

Vegetation-climate feedbacks

• Water -> Vegetation

• 1. Water controls large scale plant distribution patterns

• 2. Water controls establishment, growth and reproduction of plants

• Vegetation -> Water

• 1. Vegetation changes surface attributes that govern water and energy partitioning (albedo, roughness, soil moisture, infiltration capacity)

• 2. Vegetation contributes to precipitation recycling (i.e. the fraction of precipitation that comes from evapotranspired soil water)

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Bridging diversity sciences and earth sciences

Biosphère Atmosphère

GéosphèreHydrosphèreCryosphère

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Anthropogenic impacts on water balance

Biosphère Atmosphère

GéosphèreHydrosphèreCryosphère

Anthropospheredemographic & socio-economic changes

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Land use and land management

changesAnthropenic

climate change

Soil erosion & degradation

Increasingwater demand

A working definition of Ecohydrology

• To understand the interactions and feedbacks between hydrologicaland ecological processes at multiple temporal and spatial scales

• To understand the dynamics and the functioning of hydro-ecosystems

• To give clues for a sustainable use of natural ressources

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Key issues in ecohydrology

• Vegetation patterns in relation to water availability ?

• Biophysical processes that account for these patterns ?

• Impact of climate and land use changes on the coupled hydrological and ecological processes ?

• Incorporating vegetation dynamic in hydrological models ?

• ... over a range temporal scales : from diurnal to multi-decadal timescales.

• ... over a range of spatial scales : from the plant organ to watershed and regional scales.

Fundamentals of Ecohydrology (Philippe CHOLER – CNRS – France). Wuwei (09/2013)

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Advanced readings

• Burba, G. G. and Verma, S. B. 2001. Prairie growth, PAR albedo and seasonal distribution of energy fluxes. -Agricultural and Forest Meteorology 107: 227-240.

• Falkenmark, M. and J. Rockstrom. 2004. Balancing Water for Humans and Nature: The New Approach in Ecohydrology. Earthscan.

• Hannah, D. M., et al. 2004. Ecohydrology and hydroecology: A new paradigm'? - Hydrological Processes 18: 3439-3445.

• Koster, R. D., et al. 2004. Regions of strong coupling between soil moisture and precipitation. - Science 305: 1138-1140.

• Rietkerk, M., et al. 2000. Multiscale soil and vegetation patchiness along a gradient of herbivore impact in a semi-arid grazing system in West Africa. - Plant Ecol. 148: 207-224.

• Scanlon, T. M. and Kustas, W. P. 2010. Partitioning carbon dioxide and water vapor fluxes using correlation analysis. - Agricultural and Forest Meteorology 150: 89-99.

• Vladilo, G., et al. 2013. TThe habitable zone of earth-like planets with different levels of atmospheric pressure. -Astrophysical Journal 767:

Fundamentals of Ecohydrology (Philippe CHOLER – CNRS – France). Wuwei (09/2013)

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