The deadly Super Cyclonic Storm - Amphan - battered everything that came in the path of its 150+ km/hr winds on 21st / 22nd May 2020 - be it trees, houses, vehicles, electric poles or telephone lines. As on May 24th 2020, the situation is still far from normal - the Army has been directed to aid in rescue, relief and restoration work. With an estimated Storm Surge (abnormal rise in sea level over and above the tidal levels) of 5m and rainfall over 200mm, Amphan left a destructive trail - inundating several regions, especially the coastal regions on its path.
Using Radar (SAR) Remote Sensing, it is possible to determine the areas that are affected by flooding: In the depiction below, I have overlaid the Crisis image, dated 22nd May 2020 midnight (roughly 24 hours after the Cyclone had passed) on the Archive image, dated 23rd March 2020 to observe the extent of flooding.
Wherever there is a significant backscatter differential between the two Satellite images - the pixels have been shaded in red, implying the presence of Water which further implies the presence of Floods. The difference is due to the backscatter reflectance being much lower in the Crisis image compared to the same pixels in the Archive image. This is because Water reflects the Radar Waves away from the Satellite's Receiver (due to Specular Reflection).
Backscatter differential may not necessarily be attributed to the presence of water alone - significant changes in ground topography can also cause it.
That being said, given our awareness of the context of Crisis image i.e. in the Super Cyclone's aftermath, it is reasonable to conclude that the lower Reflectance readings across the affected areas lying on the path of Amphan is primarily due to the presence of Water in the form of Floods.
The darker the red pixels - the greater the deviation in backscatter, implying severe flooding.
Much thanks to EO-College, RUS Copernicus and OpenStreetMap for the training.
As you would observe from the map depiction above, large swathes of West Bengal and coastal North Orissa have been flooded. Naturally, the Flooded areas closely mimics the route which the Amphan cyclone took - landfall around the western edge of the Sundarbans and going north from there, towards Kolkata (which is not shown in the map depiction).
One must also appreciate the striking accuracy of the Indian Meteorological Department's Cyclone Path Forecast. It is very difficult to forecast even daily weather patterns and to predict the Cyclone's path so precisely speaks volumes about the institute's technical prowess.
One anomaly which I could spot is the relative 'lack' of Red pixels i.e. Flooded areas over the Sundarbans. After all, the world's largest contiguous mangrove forest bore the severest brunt of the Super Cyclone and should have been flooded. The possible reason contributing to this anomaly that I could think of is that the Sunderbans Delta has high surface water presence even on a normal day and the excess water from Flooding didn't make much of an impact to the Backscatter Reflectance readings (i.e. the difference between the Crisis and Archive pixels was not significant). Low tide during the time of Amphan's landfall could have also contributed towards the low differential.
What else could you spot or interpret?
Still reeling from Coronavirus, Super Cyclone Amphan brings more devastation and misery to the country of India. Let's hope that East India in particular better prepared to deal with such calamities because the cyclones are sure to strike again.
May 2023 Update: A less known, but a deadly health implication post-Cyclonic activity
As many in India would know, the East coast is a hotbed for Cyclones & Tropical Storms. For those curious as to why, here is the explanation. While rescue, relief and rehabilitation is the standard course of action, an equally important facet is the prevention of Disease. Flooding results in the creation of stagnant pools of water which becomes a breeding ground for Malaria mosquitoes as well as the other water-borne diseases. One major long-term Health risk that I became aware of today arises from Asbestos overexposure.
Asbestos? Yes, it is the same fibrous mineral which has excellent insulating properties. I was fascinating by this material during school and fondly remember posing an innocent question to my private tutor - 'Can we travel to the Sun wearing an Asbestos Spacesuit?' I distinctly remember the big grin on his face and the routine sarcasm subsequently in front of the entire classroom - 'Look, here is the boy who thinks he can travel to the Sun wearing Asbestos!' 😁
Today, I've become aware that over-exposure to Asbestos causes Mesothelioma - a deadly cancer that affects the lungs, abdomen and heart. Once the cancer-causing property of this inexpensive material was identified, its usage in home insulation - roofs, walls, concrete etc. - has significantly reduced.
How is Asbestos-induced Cancer connected to the Amphan event / Cyclones / Floods?
Asbestos' microscopic fibers become exposed and airborne when old buildings (which have asbestos in them) are ravaged by Cyclonic storms. These fibers, when inhaled, pose a significant health threat to Residents, Rescue & Relief personnel and those who come into its contact. The longer the exposure, the riskier it is. Because of lack of awareness, reducing the exposure to asbestos using appropriate Masks isn't an priority in the cyclone's aftermath.
Much thanks to Outreach Coordinator of The Mesothelioma Center - Elvira Jiménez - for reaching out and sharing this valuable information.
She specified:
"There is no known safe level of Asbestos exposure. Because of this health threat, it is highly recommended that flood-damaged Asbestos-containing material be repaired, enclosed, encapsulated or safely removed"
Below is the list of common Household materials that typically contain Asbestos-
The Mesothelioma Centre has created this detailed guide which would assist homeowners and first responders with useful information on how to minimize their exposure to asbestos in the aftermath of a natural disaster - be it a cyclone or a wildfire.
It is not just the immediate aftermath of the Cyclone which has to be dealt with, the long-term health implications arising from the disaster should also be mitigated by raising citizen awareness.
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