Ecohydrology - Philippe Cholerphilippe-choler.com/resources/Choler_Ecohydrology_Part1.pdf · • 1....
Transcript of Ecohydrology - Philippe Cholerphilippe-choler.com/resources/Choler_Ecohydrology_Part1.pdf · • 1....
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EcohydrologyPhilippe CHOLERphilippe.choler@ujf-grenoble.frwww.philippe-choler.comStaff scientist at CNRS(University of Grenoble - France)
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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
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1. What is ecohydrology ?
Fundamentals of Ecohydrology (Philippe CHOLER – CNRS – France). Wuwei (09/2013)
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Water is life
Fundamentals of Ecohydrology (Philippe CHOLER – CNRS – France). Wuwei (09/2013) Source : http://www.hpcf.upr.edu/~abel/phl/Liquid_Water.jpg
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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
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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
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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.
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Fundamentals of Ecohydrology (Philippe CHOLER – CNRS – France). Wuwei (09/2013)
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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
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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.
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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
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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
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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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