From NASA EOS Image of the Day:

Between July and September 2010, severe drought gripped the Amazon Basin. The Negro River, a tributary of the Amazon, reached its lowest level in 109 years of record-keeping, and uncontrolled fires spread a pall of smoke over the drying basin. But how did the drought affect the trees?

This image shows a possible answer. Made with vegetation “greenness” measurements from the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite, the image shows vegetation conditions between July and September 2010 compared to average conditions for the same period between 2000 and 2009 (except for 2005, another drought year). The vegetation indices are measurements of the how much photosynthesis could be happening based on how much leafy vegetation the satellite sees. In 2010, the vegetation index recorded lower values than in previous years, an indication that trees under drought stress either produced fewer leaves or the chlorophyll content of leaves was lower, or both.