ASSESSMENT OF ALBEDO CHANGES AND THEIR DRIVING FACTORS

OVER THE QINGHAI-TIBETAN PLATEAU

B. Zhang, L. Lei, Hao Zhang, L. Zhang and Z. Zen

WE4.T06.4 - Geology and Solid Earth V Location: Room 12Sension Time: July 27, 15:20 - 17:00Presentation Time: July 27, 16:20 - 16:40

Vancouver, July 27

Outlines

1. Studying area

2. Scientific problems

3. Data collected

4. Results and discussion

5. Conclusion

Average elevation: 4500m → The roof of the world (2.5 mil km2)

Qinghai-Tibetan Plateau

1. Study area

Qinghai-Tibetan Plateau

Ablation of glacier

Grassland change

global warming

Sensitive to climate change

Lake

Grasslands

Snow and glacier

Land cover map

( Liu J., Liu, M., et al. 2003)

Assessed the spatial-temporal change of land surface albedo

2. Scientific problems

Variation of surface factors driving albedo variations: snow cover, vegetation cover (NDVI)

as albedo variation is one of the key factors to impose the radiative forcing on the climate Ten year: 2000~2009

using the datasets derived from satellite observations

Albedo variations responding to the change of snow and

vegetation

What Happens? And Why? And How?What Happens? And Why? And How?

3. Data and Methodology(1)MODIS datasets included MODIS/Terra+Aqua Albedo 16-Day L3

Global 500m SIN Grid V005 (MCD43A3) (NASA) （ Albedo-ρ)

(that is available every 8-day ）

(2) MODIS/Terra Vegetation Indices 16-Day L3 Global 500m SIN Grid

V005 (MOD13A2)

(3) MODIS/Terra Snow Cover 8-day L3 Global 500m Grid (MOD10A2)

(http://lpdaac.usgs.gov/)

(4) land use map of China in 2005 ( produced by Landsat images)

(5) Temperature and precipitation data

（ measured from 2000 to 2009 on 48 meteorological stations in the Qinghai-Tibetan plateau ）

Periods: from 2000 to 2009 (ten years); coverage: 12 tiles of MODIS

3. Data and Methodology

Snow Cover frequency

All of the 8-day snow cover values were combined to create an overall

frequency of snow cover, which represents the approximate percentage of

the time during ten years(2000-2009) that snow cover could be expected.

Average of NDVI, and Albedo

M=∑V/n V---the value of NDVI or Albedo of pixel for each modis image. N—the

number of images for 10 years.

3. Data and Methodology

Inter-annal Trends of Albedo or NDVI (2000-2009)

1

/ n

i ijj

V V n

j: for values of different MODIS data within a year;

j: certain year, such as 2000, 2001

2000 2001 2009( ) _ ( , ,..., )Trends V Lst square V V V

V---the value of NDVI or Albedo of pixel for each modis image

Correlation coefficients COV(X, Y ） =E([X-E(X)][Y-E(Y)])

4. Results and discussion

1) Spatial variation of general average albedo,

average NDVI and frequency of snow cover

2) Inter-annual albedo change driven by snow

cover

3) Inter-annual summer albedo change driven by

vegetation

1) average albedo, average NDVI and frequency of snow cover from 2000 to

2009 Albedo Frequency of snow cover

NDVI• greater average albedo are corresponding to

high frequency snow cover except the desert areas

• lesser values is corresponding to larger NDVI over alpine grassland and meadow, and forests (larger than 0.4)

• correlation coefficient of albedo with snow cover is up to 0.60; with NDVI is 0. 57 for the whole area of Qinghai-Tibetan plateau

2) Inter-annual albedo change driven by snow cover

Maduo

Maduo

Variation of albedo consistently coincided with the snow cover changes

Change trend of albedo

Changes trends of snow cover

Changes trends of snow cover

Temperature increasing trend Precipitation decreasing trend

Correlation between inter-annual average albedo coverage and snow coverage over the meteorological stations calculated by a buffer area of 100 km diameter circle centered the meteorological observation station

Positive correlations between albedo and snow cover were larger almost over the areas of precipitation increases.

NDVI

Alb

edo

0.34 0.38 0.42

R² = 0.605α=0.05, FDIST=0.00800.205

0.195

0.185

0.175

Precipitation (mm)

R² = 0.711α=0.05, FDIST=0.0022

150 250 350 450

Maduo

Maduo

Change trend of summer albedo

Changes trends of summer NDVI

summer: from June to August

3) Inter-annual summer albedo change driven by vegetation

Correlation between inter-annual average summer albedo and summer NDVI over the meteorological stations calculated by a buffer area of 100 km diameter circle centered the meteorological observation station

Negative correlations between albedo and NDVI and precipitation in some regions, but positive in other regions.

Snow cover dominates in some regions, and vegetation dominates in others. The albedo change is induced both by snow change and vegetation change.

5. Conclusions

(1) Albedo sensitively change with snow cover since the albedo of snow is greatest. Increasing snow cover will increase albedo.

(2) Dual effects of decreasing snow cover and increasing temperature which strength the snow melting resulted in the albedo rising(red color) over the areas of permanent snow cover and glacier in the southern Qinghai-Tibetan plateau .

Climate warming effects in the studying area:If the temperature is rising simultaneously without greater snowfall increasing but with rainfall increase in summer, albedo will be decreased by the change of surface condition (snow cover, vegetation, soil moisture etc.), which will weaken the known cooling effects of Qinghai-Tibetan plateau.