Perhaps in a geography textbook one can find a graph in any given month, with the data provided to plot a graph of rainfall against time for each month (with the x-axis reading JFMAMJJASOND). The best place for information about precipitation and hydrology in the Amazon is at nasa.gov in their Earth Observatory program, which includes a rain rate graph. Despite the evergreen nature of the forest, the team at NASA found the Amazon’s trees and plants have an unmistakable seasonal side. Seasonal swings in the leaf area of the forest not only help make the case that light, rather than water, really limits plant growth in the tropics, but they also provide evidence that the link between the forest and the climate of the Amazon is even more intimate than scientists once supposed. In the Amazon, it seems, it’s not just the rain that makes a rainforest; the rainforest makes it rain. For nearly a decade, Ranga Myneni has been leading a team of scientists who were developing and fine-tuning the solving calculations that translate satellite observations of light reflected from Earth’s surface into measurements of how many layers of leaves are within a satellite sensor’s field of view. A plant’s leaves are the gatekeepers of the exchange of carbon dioxide and oxygen, energy, and water vapour between vegetation and the atmosphere; leaf surface area plays a critical role in carbon, water, and climate cycles on local and global scales. Contrary to many people’s pre-conceptions, in most parts of the rainforest, it doesn’t actually rain all year long: To the north of the equator, the rainy season is in the summer but the majority of the Amazon is south of the equator and over these areas, the rainy season starts somewhere around October or November and ends some time in spring. The forest stays evergreen because many trees extend roots several meters into the soil, and they redistribute the water stored deep underground to places where the soil is dry.
