Discussion: Lake level change of
Tibetan Plateau from ICESat
Papers for discussion
• Zhang, G., H. Xie, S. Kang, D. Yi, and S.F. Ackley, 2011a. Monitoring lake
level changes on the Tibetan Plateau using ICESat altimetry data (20032009). Remote Sensing of Environment. Vol.115(7): 1733-1742.
doi:10.1016/j.rse.2011.03.005 (link)
• Zhang, G., H. Xie, S. Duan, M. Tian, and D. Yi, 2011b. Water level
variation of Lake Qinghai from satellite and in-situ measurements under
climate change. Journal of Applied Remote Sensing.
doi:10.1117/1.3601363. (link)
• Phan, V., R. Lindenbergh, and M. Menenti, 2012. ICESat derived
elevation changes of Tibetan lakes between 2003 and 2009.
International Journal of Applied Earth Observation and Geoinformation.
Background of the study area
Tibetan Plateau
The Third Pole
The “water tower” of Asia
Mt. Everest
+
Mean elevation 4000m (13,123 ft)
Highest 8,840m (29,002 ft)
+0.9 °C
The temperature rise: 0.3 oC/decade, 1.8 oC over the past 50 years
Winter temperature: 2.9-4.2 oC from 1995 to 2005 (Wu et al., 2008)
(Xu et al., 2009)
Glaciers in Tibetan Plateau
(TP) retreating/melting at
accelerated rate under global
warming
Total 36,800 glaciers
Total 1500 lakes
Total 1500 lakes in Tibetan Plateau.
MODIS 500m, 261
ICESat with footprints, 111, 74 and 37
Zhang et al., 2011a, RSE
Selin Co
Nam Co
Background of ICESat
Ice, Cloud, and Land Elevation Satellite
(ICESat)
Instrument: Geoscience Laser Altimeter
System (GLAS)
Orbit Height: 600 km
Inclination: 94
Laser Wavelengths: 1064 nm and 532 nm
Orbit Repeat: 8 day and 91 day
Transmitted Pulse FWHM : 5 ns
Laser Footprint Diameter on the ground: 70
m
Sample interval on the ground: 170 m
Sample Rate: 40 laser shots per second.
Animation
Data processing and deduction
MODIS 250m, 893 lakes
ICESat footprint, 154 lakes
Phan et al., 2012
Nam Co
Relative lake level measurement since 2005
http://www.namco.itpcas.ac.cn
ICESat for lake level change
The only lake level
4725.41m, GPSed
on Nov 18, 2009.
4725.43m from
ICESat, Oct 9, 2009
s.t.d
10cm for
summer and
30cm for
winter
RANSAC (Random sample consensus algorithm). A predefined threshold
value of 15cm is used. (they actually compared 25cm, 35cm). 1° surface
sloped is assumed
Phan et al., 2012
Results
84% all lakes, 89% salt lakes with lake level increase, at mean rate 0.27m/year
67.53% increase from 0-0.4m/year
Mean increase 0.2m/year
Phan et al., 2012
Zhang et al., 2011b paper
• A case study of validation of ICESat altimetry
data and investigation of possible reasons
causing lake level change
Lake Qinghai
Lake Qinghai
Location of Lake Qinghai, and rivers, hydrological and meteorological station sites
Lake level change
Lake level change from gauge station Xiashe during 1959-2009
The 47 ICESat tracks through Lake Qinghai.
Lake level change
Zhang et al., 2011b, JARS
Lake level from in-situ station vs. ICESat data
Absolute average difference=0.06 m
RMSD=0.08 m
Annual mean runoff at stations Buha from 1956-2009
1967
L = Runoff + PLake - E
Pbasin + Glacier/Snow melting
1989
2005
1996 was a tipping point when the 5-year running
mean T lager than 0°, which accelerate the melt of
glacier/perennial snow cover.
It is reasonable to predict in the near future, another
tipping point will be reached when melting water can
not balance the water loss due to combined P and E
effects. This will result in the lake level decrease and
the lake will eventually dry out if ….
• ICESat data are used to examine 74 or 154 largest lakes in Tibetan Plateau
for lake level changes, with a mean increase rate of 0.28m/year or
0.2m/year, respectively.
• ICEsat derived lake elevations match well with gauge measurements
(R2=0.9, mean absolute error 0.06m)
• 84% of all lakes and 89% of the salt lakes show tendency of lake level
increase; the largest lake level increase, 0.80m/year, is the Lake Cedo Caka.
The largest volume increase is Selin Co, followed by Qinghai Lake and Nam
Co, the largest decrease is Yamzhog Yumco
• Increase in lake level is consistent with the accelerated glacier melting in
the region reported in many studies.