NASA Images Show Anatomy of Pakistan Flood Disaster

Feature August 20, 2010


NASA Images Show Anatomy of Pakistan Flood Disaster

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2010-274&cid=release_2010-274

In late July 2010, flooding caused by heavy monsoon rains began across several
regions of Pakistan. According to the Associated Press, the floods have affected about
one-fifth of this country of more than 170 million. Tens of thousands of villages have
been flooded, more than 1,500 people have been killed, and millions have been left
homeless. The floodwaters are not expected to recede fully before late August.

NASA's CloudSat satellite captured the genesis of the flooding event as it flew over the
region on July 28, 2010. At that time, a large area of intense thunderstorms covered
much of Pakistan. Between July 28 and 29, up to 400 millimeters (16 inches) of rain
fell from these storm cells, triggering flooding along the Indus and Kabul Rivers.
Storms with similar structures to this one have become common this summer as
tropical monsoon moisture, coupled with a strengthening La Nina (which has different
effects around the world), dominate this region's weather patterns.

The top portion of the first image, from the Moderate Resolution Imaging
Spectroradiometer (MODIS) instrument on NASA's Aqua spacecraft, reveals the bright
white cloud tops of the cluster of thunderstorms. The blue vertical line shows
CloudSat's path at the time the MODIS image was acquired. CloudSat's path cut
through a large thunderstorm cell in the northern section of the country.

The Cloudsat data are shown in the bottom portion of the first image. As seen in the
top half of the bottom image, CloudSat classified the majority of the clouds present at
the time as deep convective (cumulonimbus) clouds, typical of thunderstorms. The
bottom half of the lower image shows the 3-D vertical structure of the storm along the
satellite's flight path, revealing its heavy precipitation. CloudSat measured the cloud
heights along the radar's flight path at around 15 kilometers (9.3 miles) in the areas of
deepest convection.

The next pair of images was taken by the vertical-viewing camera on the Multi-angle
Imaging Spectroradiometer (MISR) instrument aboard NASA's Terra spacecraft. The
image on the left was taken Aug. 8, 2009, while the one on the right is from Aug. 11,
2010. These false-color views display the instrument's near-infrared, red and green
bands as shades of red, green and blue. The colors distinctly highlight the contrast
between water and vegetation on the river banks, since vegetation appears bright in
the near-infrared portion of the electromagnetic spectrum.

The region of southern Pakistan shown here includes the Sindh Province. The Indus
River, Pakistan's longest, can be seen snaking across the image from lower left to
upper right. The feature near the bottom and left of center is Manchhar Lake. Water
appears as shades of blue and cyan, though sediment content can add a tan color, as
seen in the upper right. Clouds appear white. In the image from 2009, the Indus is
typically about 1 kilometer (0.6 miles) wide. In contrast, in the 2010 image, the river is
around 23 kilometers (14 miles) wide in spots, and flooding is very evident in much of
the surrounding region, particularly in the Larkana District west of the river.

A different before-and-after perspective of the floods is provided by the next pair of
false-color images, taken by the Atmospheric Infrared Sounder (AIRS) instrument on
NASA's Aqua spacecraft using its four visible and near-infrared channels. These
images also show southern Pakistan and the Sindh Province. The Indus River
appears to enter from the upper right and winds its way southwestward toward the
lower left. The image at the left was taken before the flooding on July 9, 2010, while
the right-hand image was taken on Aug. 10, 2010.

The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER)
instrument on NASA's Terra spacecraft provides the next image, a cloud-free view over
the city of Sukkur, Pakistan, taken on Aug. 18, 2010. Sukkur, a city of a half million
residents in southeastern Pakistan's Sindh Province, is visible as the gray, urbanized
area in the lower left center of the image. It lies along the Indus River, which snakes
vertically from north to south through the image and forms the basis for the world's
largest canal-based irrigation system. As reported by the British Broadcasting
Corporation, Sukkur is one of the few urban areas in the region that has so far
escaped widespread destruction from the flooding, which has affected an estimated 4
million people in the province. Relief camps have sprung up across the city to house
some of these displaced people. The land along the Indus River in this region is
largely agricultural, and the flooding has taken a heavy toll on the region's crops and
fruit trees.

The final image was created with data from the Advanced Microwave Sounding Unit
instrument, which flies on NASA's Aqua spacecraft as part of the AIRS instrument
suite. It shows how surface emissivity—how efficiently Earth's surface radiates heat—
changed in the affected region over a 32-day period between July 11 and August 12.
Surface emission, in this case in the microwave region of the electromagnetic
spectrum, depends strongly on what type of surface is present. For dry land, surface
emission is high—measuring close to 1 (land radiates heat very efficiently); while for
water, it is quite low—measuring less than 0.5 (water tends to retain heat better than
land). The image shows that the emission dropped over this time span by up to 0.4 in
large areas surrounding the Indus River, indicating that these areas are almost
completely underwater.

Scientists can use this technique to estimate how much of the land surface has been
inundated. A significant advantage is that the technique works both day and night, and
under both clear and cloudy conditions.

For more information about CloudSat, see: http://cloudsat.atmos.colostate.edu/ and
http://www.nasa.gov/cloudsat . For more on MISR, visit: http://www-misr.jpl.nasa.gov/ .
For more on AIRS, see: http://airs.jpl.nasa.gov . For more information on ASTER, see:
http://asterweb.jpl.nasa.gov/ .

#2010-274

Alan Buis 818-354-0474
Jet Propulsion Laboratory, Pasadena, Calif.
Alan.buis@jpl.nasa.gov

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