Ecohydrology

Philippe CHOLER [email protected] www.philippe-choler.com Staff scientist at CNRS (University of Grenoble - France) Outline of the lectures Lecture 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 1 Water phase diagram

Point critique 374°C - 219 atm

25°C, 80% RH,

pw ≈ 2530 Pa

5°C, 20% RH,

pw ≈ 174 Pa

Enthalpies de changement d'état: Fusion 6kJ mol-1 Ebullition 40.7 kJ mol-1 solid liquid Enthalpies de changement d'état: precipitation precipitation Fusion 6kJ mol-1 Vaporisation 40.7 kJ mol-1 Dependence of the HZ to atmospheric effects

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) Source: Vladilo G., et al. (2013) Astrophysical Journal, 767. Fundamentals of Ecohydrology (Philippe CHOLER – CNRS – France). Wuwei (09/2013) 1 The water balance

Precipitation – Evapo- "Blue" "Green" Rainfalls (P) Transpiration (ET) water water

Bassin versant – Watershed – river basin vapor

Surface (R1) & Subsurface (R2) Runoff - Ruissellement (R) Partitioning 1 Runoff vs. Soil infiltration R1

Partitioning 2 Evapotranspiration vs. groundwater recharge R2

Groundwater

Streamflow temporally lagged, spatial integral of runoff over a river basin

Fundamentals of Ecohydrology (Philippe CHOLER – CNRS – France). Wuwei (09/2013) 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. 1 Coupling between water and energy balance

Flux radiatif net

(RN) radiation (Net Radiation) convection

Rayonnement net "Green" water conduction Flux de chaleur Flux de chaleur Flux de chaleur Latente (H ) L Sensible (H) dans le sol (HG) (Latent Heat Flux) (Sensible Heat Flux) (Ground Heat Flux)

Ta

Ts

Apport d'énergie Pertes d'énergie

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

RN = H + HL + HG

HL =  ET -2 -1 ET évapotranspiration : en kg m s d’eau échangée  : chaleur latente de vaporisation de l'eau (latent heat of vaporization of water). 1 Example of daily time course of fluxes ) -2 m -1 (J s

Flux d’énergie échangés au-dessus d'un champ d'avoine (énergie par unité de temps et de surface) (d'après Long & al 1964)

Le jour, une très large part de l’énergie incidente est utilisée pour l’évapotranspiration 1 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 e Ci i Assimilation nette (An)

An = g (Ca - Ci)/P Cs tot,CO2 atm es Ca Cx pression partielle de CO2 (chambre sous-stomatique, surface foliaire, atmosphère) ea couche CO2 H2O limite gCO2 conductance stomatique au CO2 1 Coupling between water and carbon cycles

CO2 A perfect anti-correlation between

measurements of CO2 and water vapor concentration is predicted if exchanges are only controlled by stomata (Monin-Obukhov Similarity Theory) H2O

WUE : Water Use Efficiency = An / T

Source: Scanlon T.M. & Kustas W.P. (2010) Agricultural and Forest Meteorology, 150, 89-99. 1 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. 1 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)

Plant responses to precipitation in semi-arid grasslands 1 Bridging diversity sciences and earth sciences

Biosphère Atmosphère

Hydrosphère Géosphère Cryosphère 1 Anthropogenic impacts on water balance

Anthroposphere demographic & socio-economic changes

Land use and land management Anthropenic changes climate change

Biosphère Atmosphère

Hydrosphère Géosphère Cryosphère

Increasing Soil erosion & water demand degradation 1 A working definition of Ecohydrology

• To understand the interactions and feedbacks between hydrological and 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 1 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) 1 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)