Monsoon floods in Pakistan during September 2012 have killed more than 400 people and affected more than 4.5 million others, according to the government disaster relief agency.
In southern Pakistan, where the borders of Punjab, Balochistan and Sindh provinces meet, a network of levees and canals diverts water from the Indus River to thirsty agricultural fields. Water is usually scarce in Pakistan, but heavy monsoon rains can overwhelm the country's irrigation infrastructure, as they did in the summer of 2010.
Flood conditions returned in the summer of 2012. These before-and-after images, captured by NASA's Terra satellite onSept. 1, 2012, and the agency's Aqua satellite on Sept. 21, show part of the irrigation infrastructure west of the Indus River.
Both images use a combination of visible and infrared light to increase contrast between water and land. Water varies in color from electric blue to navy. Vegetation is bright green, and bare ground is pink-beige. Clouds are pale blue-green and cast shadows.
The relatively pale blue of the water in the Indus River suggests it is carrying heavy loads of sediment, a common occurrence during floods. In the northwest (image upper left), the pale blue suggests shallow water on a floodplain. Darker shades of blue indicate greater water depths. Deep water appears to cover large stretches of land, much of it along the edges of irrigation infrastructure, which has unnaturally straight and even contours.
Images courtesy of NASA.