An animation showing biomass burning in Central Africa


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The above animation shows a close-up of images taken from satellite of the same area over Central Africa just south-east of Lake Chad. There are many interesting changes that can be clearly seen. Over the span of four months (from October of 2000 to February of 2001), this part of the world undergoes a striking transformation. To the north (just one screen above this one) is the southern edge of the world's largest desert, the Sahara Desert. To the south lies a year-round, lush rainforest. This in-the-middle area is commonly called the Sahel region, and it fluctuates north-south throughout the year as the seasons change. Over the course of the summer, a large mass of moist, ascending air (called the Inter-Tropical Convergence Zone, or ITCZ) begins to shift north. As it migrates toward the desert boundary, it dumps persistent quantities of rain over the landscape until late summer, and plants begin to grow vigorously, as shown in green in this animation. By late September, the vegetation cover is at a maximum. The desert to the north slowly encroaches southward into this view by the early winter. As the temperature begins to increase, the plants drop leaves in order to prevent drying out. It is at this stage (by November) that the vegetation is at risk of fire. Either by natural causes or set by humans, the vegetation burns easily over a large areas visible from space. After the fire dies away, the landscape is converted from savanna grassland to dark stumps and ash. These dark areas are often called "fire scars," and from the animation above, it is easy to see why. For cultivated agriculture, farmers sometimes intentionally set controlled fires on their property after a harvest to accelerate the growth of new plants for the next growing season. By looking closely, it is possible to even see fire scars from the previous year across the image. Notice the large amount of water flowing in the river during the wet season (the first few frames). By February, the river is hardly noticeable, as it has been reduced to a nearly dried-up stream. Also visible are the ancient, thread-like riverbeds in the low-land area in the upper-left corner.


Credit: Dylan Prentiss, Department of Geography, University of California, Santa Barbara

For more info: http://www.geog.ucsb.edu/~dylan/mtpe/biosphere/topics/veg/fires.html