ESA - Eduspace EN - Weather and Climate - Exercise 3 - The summer monsoon and its floods

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Exercise 3 - The summer monsoon and its floods

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SPOT-X image of Bangladesh before the 1988 floods

The Ganges before and after the 1988 monsoon

Every year the summer monsoon claims lives and causes damage within the Himalayan region and the Indian subcontinent.

During the 2004 Monsoon, 2 208 people died in India, Pakistan, Bangladesh and Nepal. Half of Bangladesh was flooded, and damage amounted to about 2 billion US$. However, the monsoon had arrived later and was not as intense as usual. Farmers in the region suffered heavy crop damage. After the floods had subsided, about 20 million people were forced to rely on food aid.

The summer monsoon brings death and desolation to the people of South and South-East Asia. But at the same time it also brings the necessary rain that breathes new life into this region. This makes the summer monsoon both a blessing and a curse.

Download the SPOT XS images of Bangladesh before and after the 1988 floods.

These two images show part of the river Ganges in Bangladesh. They were taken in 1987, before the monsoon, and in 1988, after the monsoon. Flooding in 1988 claimed the lives of 1 800 people. 5 million people became homeless and 3 million tons of crops were destroyed.


	SPOT-X image of Bangladesh after the 1988 floods

The situation in Bangladesh is particularly difficult. If there is not enough rain during the monsoon, the harvest will wither and there will be a dearth. If there is too much rain there will be flooding, which will likewise destroy the harvest.

The extent of the floods is clearly visible from the Spot XS image of 10 October 1988, when compared to the image of 9 January 1987. Flooding of the Ganges river extends far beyond the banks of the river itself. We will measure how far it extends in this exercise.

Download the images and save them in a folder called 'Monsoon'. Both images are GeoTiffs and are in a UTM projection. The ground resolution is 50 m. This means that one pixel equals 50 metres.

Transformation Method: UTM
Datum Name: WGS84
Ellipsoid Name: WGS84
UTM Zone: 46
UTM Hemisphere: North

Before drawing the polygon you have to decide which surfaces in the image are water.

Answer the following questions to be able to separate water from land:

Explain the different colours in the image. Which colours can be associated with water?

Why are there different colours for water?

Explain the geographical and physical background for areas of water, and provide different options to explain the differences in colouring.

Open the image bangladesh_881010.tif in LEOWorks and choose Image>Measure tool. Choose Units>Meters and draw a polygon clockwise around the water surface starting from the North-Eastern edge of the image. Close the polygon by clicking on the right mouse button.

The circumference and the surface or area measured appears in the measure tool. Convert the measured area from square metres to square kilometres and write it down.

Now open the second image, bangladesh_870109.tif, and measure the area of the water surface. Convert the result into square kilometres and calculate the dimension of the flooded area using the two results. Calculate the area covered by the images. The image size is 894 x 655 pixel with 50 metres per pixel. Calculate the percentage of water surface in both images and compare the two results.

What percentage is the change?

How many square kilometres does that represent?

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