Conventional altimetry for monitoring lake level changes and

improvements from SWOT

SWOT Hydrology Workshop, Sept 15-17OSU, Colombus

Jean-François Crétaux

What can we learn about lakes From altimetry ?

Global point of view

Regional point of view

Impact of Climate Global change

Anthropogenic impact

Assessment of the State of the Art:

• Forces and limitations of classical altimetry• End users and potential applications• New implication of SWOT mission for lakes

End users and potential applications

Regional Lake management in different perspectives depending on:

climate condition and variability (Arid, Semi-arid, mountaineering, tropical …)water uses purposes (supply for population, industry, agriculture, fishingtourism, navigation)Geopolitical issues: Transboundary water management

Global scale: Multiple Interactions and issues with

hydrological water cycleCarbon and Methane storage and emissionimpact of artificial reservoirs on Global Sea Level Rise

End users:

• national hydrological services and decision makers• international institution and programs: WMO, GEO, GIEC, ILEC, ICOLD ...• Interstate Commission for Water coordination: IFAS (Central Asia),Commission for Lakes Titicaca or Geneva, IJC (Canada/US) …..

• Hydrologists, and climatologists

« Classical » radar altimetry

SWOT

Nadir radar with profiling mode acquisition and intertrack from 70 to 350 km at the equateur10 days to 35 days repeat orbitData: height level over water surfaceAccuracy over lakes highly variable (from 5/6 to 50/60 cm)Ku, C and S bands

Ka Band wide-swath radar altimeter + Nadir altimeter10-20 days repeat orbit Data: height water and storage Image pixel of ~100 mPossibility to derive slope along rivers with 1cm/km VresExcepted accuracy over lakes ~5-10cm

Lakes of Tibetan plateau:IPCC prediction is 1.4 to 5.8 ° increasing for the next 100 yrsÞRecession of Glaciers, floods, surplus of water feeding lakes in a first step, followed by strong reduceÞWater resource stress predicted in the futureÞNeed of precise & full monitoring of lakes and riversÞClassical altimetry insufficiant: 1 lake is monitored in theCentral tidetan plateau (Ziling), another one in the NE (Qinghai)

Lakes from radar altimetry, current results and limitations (1/3):

SWOT: Level and surface time series over dozenof lakes is potentially possibleÞWill serve as proxy for climate changeimpact in the Hymalaya region

Lakes level from Envisat’s35 days repeat orbit

climate change issue

Toktogul reservoir, altimetry(green), in situ(red)

840850860870880890900910

1992 1994 1996 1998 2000 2002 2004 2006 2008

Date (year)le

vel (

m)

Sarykamish from altimetry

0

1

2

3

4

5

6

7

8

1990 1995 2000 2005 2010Date (year)

Leve

l (m)

Issykkul, Altimetry (green), In-situ (Red)

1605,81606

1606,21606,41606,61606,8

16071607,2

1992 1994 1996 1998 2000 2002 2004 2006 2008

Date (year)

leve

l (m

)

Chardarya, altimetry(green), in situ (red)

240242244246248250252254256258

1993 1995 1997 1999 2001 2003 2005 2007

date (year)

level

(m)

Lakes from radar altimetry, current results and limitations (2/3): Climate change and transboundary water management issue

Central Asian river’s flow is changed by acceleration of glaciers melting, variability in rain regime, irrigation and artificial reservoirs regulation under interstate agreements. Complex system, hard political framework, and lack of ground network for free water information delivery and sharing. 5 countries with around 50 million of people leaving.

Small reservoirs not monitored by altimetry & river’s flow not available => potential to enhance cooperationbetween countries through a system like SWOT who doesn’tcare of « boundaries », better knowledge on water storage and dynamics, and support to decision makers and scientists

Impact of Southern Oscillation ?Impact of El Nino ?Impact of PDO ?Impact of Glaciar melting?Impact of Precipitation?

Llanquihue

50.2

50.4

50.6

50.8

51

51.2

51.4

2002.5 2003 2003.5 2004 2004.5 2005 2005.5 2006

Date (year)

level

(m)

-

Lake Argentino

177

177,5

178

178,5

179

179,5

180

180,5

181

181,5

1992 1994 1996 1998 2000 2002 2004 2006 2008

date (year)

level

(m)

-Lakes from radar altimetry, current results and limitations (3/3): Inter-annual climate variability

Lake San Martin

251

252

253

254

255

256

257

2001 2002 2003 2004 2005 2006 2007 2008

Date (year)

level

(m)

-

Ranco

62

62.5

63

63.5

64

64.5

65

65.5

66

2002.5 2003 2003.5 2004 2004.5 2005 2005.5 2006Date (year)

level

(m)

-

Radar altimetry not suitableTo catch geographycalpatterns connected tointer-annual climate variability in Andean lakes(<10 lakes monitored withPoor precision)

SWOT: Level / surface variations for more than 100 lakes all along the Andean is Excepted to improve knowledge on water balance changes under various climate forcing

~1900

2000

Construction of dams has vastly altered the water cycle by:•Altering the seasonal cycle, and annual amount of discharge (6 major global rivers no longer flow at their mouths)

•Increasing the time of travel through the channel system

•Changing the quality of rivers, and constituents and physical characteristics of continental river discharge

•Transporting water within and between rivers basins, and altering its partitioning (usually meaning increased evapotranspiration)

•Slow down the GLSR

Impacts of reservoirs on the water cycle ?

Recent calculation based on ICOLD database showed thatover 100 yr, ~11000 km2 of water inpoundmentrepresents ~ -0.55mm/yr on GSLR (Chao et al., 2008)

Lakes and inland seas contributes to ~ +0.1 mm/yr over last 2 decades

Large errors due to -Small Lakes & reservoirs and remote areas less monitored in level and surface-accounting of global abundance and size distribution of lakes and

reservoirs is uncomplete and under-estimated (downing et al., 2006)ÞTheir dynamic is consequently not know at global scale

-Usage of reservoirs has significant storage fluctuation

Impacts of reservoirs on GSLR ?

Current altimetry miss numerous small water bodiesTotal accounting is impossible

SWOT may offer a valuable alternative to fullfill this purpose

Powell

1080

1085

1090

1095

1100

1105

1110

1115

1120

1125

1130

1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

date

wat

er le

vel [

m]

Hydroweb InSitu NO BIAIS

Highlight of difficulties through the Lake Powell case study

Powell

0

100

200

300

400

500

600

700

1085 1090 1095 1100 1105 1110 1115 1120 1125 1130water level [m]

surf

ace

squa

re K

m

Landsat & In situ Landsat & altimetrie

Powell dV m^3 R2 = 0.9983 R2 = 0.8821

1.E+09

2.E+09

2.E+09

3.E+09

3.E+09

4.E+09

4.E+09

5.E+09

5.E+09

6.E+09

6.E+09

1.E+09 2.E+09 2.E+09 3.E+09 3.E+09 4.E+09 4.E+09 5.E+09 5.E+09 6.E+09 6.E+09

dV calculé

dV In

Situ

dV avec InSitu dV avec altimetrie Linéaire (dV avec InSitu) Linéaire (dV avec altimetrie)

Storage variation of Lake Powel

05

101520253035

1980 1990 2000 2010

year

km

3

-

-Interannual variability-Complex shape-High sensitivity to Small errors-Thousands of worldwidereservoirs

Lake Poyang in China: an example of potential use of SWOT forLake water balance and hydrodynamic understanding

1000 km2< Surface < 4000 km2

Very complex flood sequences of lake Poyangthat need to be studied from remote sensing

including altimetry

Different storage areas at different heights

3

1 Channel linking Poyang lake to Yangtse

2 Small lateral lakes

2

1

2

2

2

3

Fuhe delta and Poyang bassin

Different storage areas filled at different periods

Interannual fluctuations

Numerous tributaries and outflows channels

1

2

3

6

1

Tracks of T/PTracks of ENVISAT

980 163

45

-Heterogeneous distribution of radar altimetry bins-Potential problems due to presence of vegetation-Retracking mode not adapted-Presence of water at a time given by modis

Sept 21 2004

Sept 14, 2006

Modis 21 Sept, 2004

Modis multispectral images

0

1000

2000

3000

4000

5000

6000

7000

1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009Year

surf

ace

(km

2)

-

radar altimetry+

SWOT:Spatial resolution of 100 m + vertical resolution of 1kmcombined (or not) with future RS system like MODIS or MERIS On weekly basis will allow the monitoring and mapping of flooding process over a long period of time with enough precision to assimilate measurement in Lake Poyang or similar lake in hydrodynamical model

Conclusion Some arguments for SWOT in lake’s study

Local or regional point of view

Global point of view

Water balance of individual lakesLakes are good proxies of regional impact of Climate variabilityWater management in river basins with articificial reservoirs is criticalHydrodynamic features of complex shallow lakes (Poyang, Tchad, Altiplano Salars …)

Measurement of lakes and reservoirs global distribution and their storage variabilityContribution to GSLR would be accurately established