why does it rain everyday in the rainforest

Deforestation can lead to droughts hundreds of miles away. Rain-making rainforests. I m Bob Hirshon and this is Science Update. Cutting down rainforests in one region can deprive farms in other regions of rainfall. This according to British researchers reporting in the journal
Nature. University of Leeds environmental scientist Dominick Spracklen says they used newly available NASA satellite data, which tracks both forest cover and rainfall in the tropics. And we use our model to predict where air has come from over the past ten days, at any location in the tropics. They found that air masses that had passed over large areas of forest provided more rainfall than air masses that had not. And forests in the Amazon and the Congo support rainfall in several key agricultural areas. Spracklen says that other countries should follow Brazil s lead in curbing deforestation, since depleting forests within their borders could affect not only their own food supply, but their neighbors as well.


I m Bob Hirshon for AAAS, the Science Society. It's long been believed that leafy plants like trees contribute to rainfall. That's because they absorb water from the soil, and secrete water droplets through their leaves (a sweat-like process called transpiration ). Presumably, those water droplets end up in the atmosphere and eventually fall back as rain. If not for the plants, the same amount of water would mostly remain trapped in the soil. Using what we know about transpiration and atmospheric patterns, computer modeling studies have projected that removing large amounts of forests would result in decreased rainfall elsewhere. What's new about this study is that it incorporated numerical data from the past. Specifically, a NASA project called the Tropical Rainfall Measuring Mission (TRMM) has been closely tracking rainfall in tropical areas. By combining past measurements from TRMM with changes in rainforest cover (also tracked by satellite data), along with advanced knowledge of wind patterns, the researchers were able to design a new kind of computer model that can calculate exactly where air masses have traveled over the last ten days.


The model analyzes the amount of forest in that ten-day path, and compares it to how much rainfall that air mass produced after passing over it. The researchers found that the more forest an air mass passes over, the more rain it releases later sometimes in areas hundreds or thousands of miles away. That's significant because tropical areas include not only shrinking rainforests, but farmland that's critical to the global economy. The researchers estimate that on our current course, rainfall in the Amazon basin could decline by up to 21 percent by the middle of the century enough to take a serious toll on crops. And it stands to reason that temperate forests affect rainfall as well. The findings provide yet another reason why preserving rainforests is important. Not only could deforestation affect crop supplies, it could also set off international conflicts, in which a country with failing farms blames a neighboring country for destroying its own forests.


What was already suspected about the relationship between rainforests and rainfall? How did this study add to that knowledge? What was different about it? Why is it especially significant that deforestation can impact rainfall hundreds or thousands of miles away? Send us feedback about this Science Update Tropical rainforests are warm and wet. The soil in the rainforest is nutrient-rich. The warm, wet conditions cause vegetation and animals to rot very quickly once they've died. Decaying plants and animals get recycled back into the soil. More than half of the world's species live in tropical rainforests. Some scientists think the number could be as high as 90 percent! The moisture and the warm temperatures in the tropical rainforest are perfect for sustaining lots of different species of plants and animals.


What's the Point? Trees in the tropical rainforest can grow very tall. Leaves are usually thick and have pointed drip tips to help rain roll off them. Tree trunks are wide and flared and tree bark is thin and smooth. Some trees have roots that are above the ground. The tropical rainforest is also home to bromeliads. These are plants that collect water in their centers. The water forms pools that can support miniature ecosystems! Many of these pools support bacteria, insects, crustaceans, tadpoles, frogs and even birds! The rainforest is also home to epiphytes. Epiphytes don't grow in the soil. They grow on a host plant, usualy a tree, and get their nutrients from the moisture and dust in the air. PFerns, lichens, mosses, orchids, and bromeliads are all epiphytes. The tropical rainforest is also home to nepenthes or pitcher plants. These are plants that grow in the soil. They have leaves that form a cup where moisture gathers. Pitcher plants capture insects in these cups!

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