surface conductance and evaporation from 1- km to continental scales using remote sensing ray...

Surface conductance and evaporation from 1-km to continental scales using remote sensing

Ray Leuning, Yonqiang Zhang, Amelie Rajaud, Helen Cleugh, Francis Chiew, Lu Zhang & Kevin Tu

CSIRO Marine & Atmospheric Research, CSIRO Land & Water5 February 2008

CSIRO. Surface conductance and evaporation from 1-km to continental scales using remote sensing

The challenge

Estimate energy & water fluxes at multiple scales


• where

MODIS evaporation – a “new” approach

• Penman-Monteith equation for surface evaporation:

( / )

1 /p a a

surfacea s

A c D GE

G G

available energy

water vapor deficit

aerodynamicconductance

surfaceconductance - we model th is

a

a

s

A

D

G

G

s /


• PM equation for surface & canopy evaporation

• fraction f of equilibrium rate at soil surface:

Surface evaporation = canopy + soil evaporation

/ (1 ) /

1 / 1 / 1

surface canopy soil

a i a i

a s a c

G G G G f

G G G G

surface canopy soilE E E

• where

'climatological conductance'( / )i

p a

AG

c D

/ = exp ( - )s A aiA A k L MODIS15A2remote sensing


Canopy conductance

• Canopy conductance

(after Kelliher et al., 1995; Leuning, 1995)

50

50 50

1ln

exp( ) 1 /

stomatal light humiditydeficit

sx hc

Q h Q a

g Q QG

k Q k L Q D D


Gs sensitivity analysis

2.0

0.5800

200

0.003

0.009

0.8

0.2

D A

gsxf


Time series for Fluxnet sites: meas eqE E

Deciduous Evergreen

1eq

AE


Time series for Fluxnet sites: meas eqE E

Conifer Savanna

1eq

AE


Eeq & ERS versus Emeas for 15 FluxNet sites

(c) (d)

Eeq - Equilibrium evaporationERS - PM Equation with Gs & MODIS LAI

Emeas (mm/d) Emeas (mm/d)

Eeq (

mm

/d)

ER

S (m

m/d

)

2 free parameters: gsx & f


Application of ERS to Murray Darling Basin

• Long-term water balances of gauged catchments

0 aswav

av

SP E R t

t

• Thus

as avE P R t

• Invert evaporation model to solve for gsx & f in model for Gs

• Parameters for 3 rainfall zones from 135 catchments,

450, 450 750, 750 mm/yrP P P


Landcover & gauged catchments – Murray Darling Basin


Data

• Meteorological data

• Daily values of solar radiation, Tmin, Tmax and H2O vapor pressure from SILO

database, 2000-2005

• MODIS data 2000-2005

• 8-day/1km MOD15A2 LAI from Distributed Active Archive Center of NASA,

• Yearly/1km MOD12 land cover

• Runoff + rainfall data

• Daily runoff at 135 gauged catchments of MDB

• Daily precipitation from SILO


Time series of E, P & Lai for two catchmentsnear Tumbarumba


5-year average ERS vs EWB for 135 catchments

y = 1.05x

R2 = 0.61

200

400

600

800

1000

200 400 600 800 1000

EWB (mm/yr)

ER

S (

mm

/yr)


P & ERS – Murray Darling Basin


BudykoRemote sensing

Water balanceZhang

Energy limit

Water supply limit


Runoff: RRs and RBudyko

y = 0.80x

R2 = 0.81

0

200

400

600

800

0 200 400 600 800

Rmeas (mm/yr)

RR

S (

mm

/yr)

y = 0.87x

R2 = 0.59

0

200

400

600

800

0 200 400 600 800

Rmeas (mm/yr)R

Bud

yko

(mm

/yr)

if , 0RSE P R


Runoff maps


Conclusions and further work

• PM equation, Gs model & MODIS Lai

• Builds in energy balance from start

• useful for estimating evaporation at catchment scale

• Gs model – biophysical with two parameters gsx and f

• Overestimation of E due to uncertainties in • MODIS Lai

• Single value of f for each rainfall zone – should be variable

• No constraint by water balance

• Further work• Combine PM combination equation with catchment water balance

• Improve soil evaporation component • Use microwave remote sensing for f?

Contact UsPhone: 1300 363 400 or +61 3 9545 2176

Email: [email protected] Web: www.csiro.au

Thank you

CSIRO Marine & Atmospheric ResearchRay Leuning

Phone: 61 2 6246 5557Email: [email protected]://www.dar.csiro.au/lai/ozflux/

surface conductance and evaporation from 1- km to continental scales using remote sensing ray...

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