Characterization of the Water and Energy Cycles in the Agro-Pastoral Sahel, in a Context of Climate and Land-Use Changes

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Characterization of the Water and Energy Cycles in the Agro-Pastoral Sahel, in a Context of Climate and Land-Use Changes

C. Leauthaud ¹ , J. Demarty ² , B. Cappelaere ² , M. Grippa ³ , B. Sultan ⁴ , L. Kergoat ³ , T. Vischel ⁵ , C. Velluet ²

1

CNRS, Hydrosciences

²

IRD Hydrosciences

³

GET Géosciences Environnement Toulouse

⁴

IRD-LOCEAN

⁵

CNRS-INSU, LTHE

References

Contact information Results

Methodology

Objectives Context

!

I. Reconstitute a high-resolution continuous dataset of climatic data for Central Sahel II. Evaluate coupling of vegetation and SVAT models

III. Estimate modifications of water and energy cycles for Central Sahel during 1950-2009

!  Societal:

-  Strong population growth -  Mostly rural population -  High vulnerability

!  Scientific:

-  Strong climatic variability -  Changes in land-cover -  Importance of surface-atmosphere

interactions in the water, energy and vegetation cycles

How have the water and energy cycles evolved during 1950-2009

for the fallow-savannah land cover type in the Sahel?

I. Data set

Conclusion & Perspectives

II. Coupling

!  Variables: Rainfall, Air Temperature, Specific Humidity, Short- and Long-Wave Radiation, Wind speed, Air Pressure

!  Advantages: continuous, high-resolution (30-min), estimation of uncertainty, good representation of annual, seasonal, daily and subdaily cycles

!  Drawback: not gridded

!  Improved rainfall- transpiration relationships

!  Mainly affects transpiration &

evaporation

III. Water and Energy cycles

!  Evapotranspiration: ~80% budget

!  Strong " of Ev & Tr in the 1980s

!  Strong seasonal signal of energy and water cycles, modulated by rainfall pattern

50-60s

‘wet’ 70s-80s

‘dry’ 1990- 2000s P 585 468 539

Ev 327 275 310

Tr 150 135 150

R 82 55 72

D 25 3 9

RN 66 65 67

LE 36 31 35

H 30 34 32

Annual mean of climatic variables at Niamey, Niger, 1950-2009

1. Comparison of annual components of the water cycle between a coupled and non-coupled version of SiSPAT, and 2. their relationship to rainfall

Annual values: Anomalies of the components of the water cycle

Seasonal cycle: 30-day moving average of the components of the water and energy budget per decade.

Average values for the components of the water and energy cycles for three climatologically distinct periods.

P 5min Climate data

3h Complementary

data (12h/24h) Quality control

Interpolation Class analysis Aggregation Aggregation

Spline interpolation Aggrega

tion

Artificial neural networks

O utp ut d ata P, Ta, RH, SH, Rg, Ra, U, Pa 30min 1950-2009 R ec on sti tu tio n M eth od s In pu t d ata

I. Data set II. Coupling

III. Water and Energy cycles

SiSPAT

Vertical 1D RN

H

Sol Végétation Atmosphère

R

G

I

D Tr

Ev P

S Braud et al., 1995

Braud et al., 1997

LAI

R

!  Iterative coupling until convergence of the exchanged variables

!  Parametrisation: Velluet et al. 2014; Boone et al., 2009

Climate data

STEP SiSPAT STEP SiSPAT

Net radiation (RN) Latent heat (LE) Sensible Heat (H) Evaporation (Ev) Transpiration (Tr) Runoff (R) Drainage (D)

P: Rainfall Ta: air temperature RH/SH: relative/specific humidity U: wind force Pa: air pressure Rg/Ra: short/long wave radiation

Leduc et al., 2001

LAI LAI

R

ESCAPE:

https://skyros.locean-ipsl.upmc.fr/~ESCAPE/

AMMA-CATCH:

http://www.amma-catch.org/

Crystele Leauthaud leauthaud@gmail.com Twin oral presentation:

Friday 19

^th

10:20 AM Moscone West 3003

!  Climatic dataset: publicly available for application in land-surface-atmosphere studies

!  Coupling: state-of-the-art estimations of surface vegetation-water-energy budgets

!  First continuous estimation of water and energy cycle components for fallow ecosystem cover in Central Sahel Next steps:

!  Sensitivity analysis on vegetation characteristics

!  Application to the millet-type ecosystem

Boone, A., Getirana, A. C., Demarty, J., Cappelaere, B., Galle, S., Grippa, M., ... &

Vischel, T. (2009). The African Monsoon Multidisciplinary Analyses (AMMA) Land surface Model Intercomparison Project Phase 2 (ALMIP2). Gewex News, 19(4), 9-10.

Braud, I., Dantas-Antonino, A. C., Vauclin, M., Thony, J. L., & Ruelle, P. (1995). A simple soil-plant-atmosphere transfer model (SiSPAT) development and field verification. Journal of Hydrology, 166(3), 213-250.

Braud, I. (1996). SiSPAT user’s manual. Simple Soil Plant Atmosphere Transfer Model, Version, 2.

Leduc, C., Favreau, G., & Schroeter, P. (2001). Long-term rise in a Sahelian water- table: The Continental Terminal in south-west Niger. Journal of hydrology, 243(1), 43-54.

Mougin E. , Loseen D., Rambal S., Gaston A., Hiernaux P. (1995). A regional sahelian grassland model to be coupled with multispectral satellite data .1. model description and validation. Remote Sensing of Environment, 52(3):181–193.

Velluet C., Demarty J., Cappelaere B. , Braud I., et al. (in print) Building a field- and model-based climatology of local water and energy cycles in the cultivated Sahel – annual budgets and seasonality. HESS.

Niamey

1. 2.

−5 0 5 10

Rainfall

0 2 4

Evaporation

−2 0 2 4

Transpiration

−1 0 1 2

Runoff

−0.5 0 0.5 1

Drainage

Apr May Jun Jul Aug Sep Oct Nov Dec

−100 0 100 200

Soil stock

1950 1960 1970 1980 1990 2000

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

0 50 100 150

Components of the energy cycle (W/m2): RN, H, LE, G

1950 1960 1970 1980 1990 2000

−100 0 100 200

Soil stock

1950 1960 1970 1980 1990 2000 ^1950s ^2000s

Mougin et al., 1995 Vegetation model

SVATmodel

100 200 300 400 500

Evaporation (mm/yr)

50 100 150 200 250

Transpiration (mm/yr)

Non−coupled Coupled

0 50 100 150 200 250

Runoff (mm/yr)

200 300 400 500 600 700 800 900 1000

0 50 100 150 200

Drainage at 4m (mm/yr)

Rainfall (mm/yr)

P Ev

Tr R D

Ev Tr R D P

55-58%

25-29%

80-87%

% o f P

P

!

Characterization of the Water and Energy Cycles in the Agro-Pastoral Sahel, in a Context of Climate and Land-Use Changes