By John Bradley
Forests bring rain. They sustain the atmospheric moisture that is needed for precipitation in a local region and in distant communities. When forests are degraded or cleared over time, weather patterns are often changed and may contribute to drought or aridification. In these
areas that have lost precipitation, reforestation and other regenerative approaches may restore more sustainable weather patterns.
Forests are essential for sustainability and provide many ecological benefits, both locally and beyond its region. In climate and ecology, forests serve as nature’s vast sink for carbon. In this article I am focusing on forests' role in the water cycle and the effect on climate when forests are degraded. The water cycle is the process of how water is recycled through the earth’s ecosystems and supports life.
A forest, to be a sustainable ecosystem, requires broad biodiversity over extensive areas. As forests’ size increases in area, its impact on climate increases. As was discussed in the last issue of this newsletter, trees contribute moisture to the atmosphere through evapotranspiration; much of this moisture is recycled precipitation from past rains that have infiltrated the soils and fed the trees for continuous photosynthesis and transpiration. Over 40% of rainfall is recycled precipitation. This recycling of water to atmospheric moisture is essential for local and distant rainfall. Removing forests reduces moisture and may prevent the formation of rain.
Healthy forests covering a significant land surface can bring rain thousands of miles inland, far from an ocean. One of the climatological processes at work is called the Biotic Pump. When the many trees of a forest evapotranspire moisture into the atmosphere, the vast amount of rising water vapor that condenses into clouds creates a low pressure area. Air from nearby high pressure areas is sucked in, bringing additional moisture, adding to the moisture and clouds to make more rain. As air mass moves across a continent, this process is continually replicated, with forests or other vegetation adding to the moisture and enabling rainfall locally and beyond. This is how rain is brought deeply inland on the continents. The mechanics of the Biotic Pump are explained in this 3 minute video.
This process continues unless trees and other vegetation are removed from the land surface. Deforestation reduces the moisture transpired into the atmosphere and lessens downwind rainfall. At scale, this may contribute to drought and aridification further down-weather. Extensive deforestation has occurred on all continents to make way for agriculture, urbanization, and extractive industries. The new land uses with minimal vegetation also add heat to the atmosphere, captured by greenhouse gasses. All these changes across the planet have disrupted weather patterns. As a result, land use disruption coupled with warming temperatures triggers or aggravates what is referred to as the drought-flood cycle. Land use change in one area reduces rainfall in a downwind area causing dryness and drought, setting the stage for wildfires and more torrential rains occur elsewhere, as has happened in the Mediterranean basin. Across the planet, there are many similar cases.
The news is filled with stories of extended drought and wildfires on the one hand, and torrential rain with flooding on the other . Many of these fires and floods are directly attributable to decades if not centuries of deforestation to support agriculture, urbanization, extractive industries and industrial development. Deforestation reduces atmospheric moisture and increases the bare land or urban heat islands warming the atmosphere. This past summer we saw drought and wildfires in Portugal, Greece, California, and other countries. While global warming from greenhouse gasses are major causes of these conditions, deforestation and land use change further disrupt nature’s ability to regulate the climate and put our human habitats increasingly at risk. Over half of the planet’s forests have been eliminated in recent centuries.
NYS and the Hudson Valley seem to be more ecologically resilient than many parts of the US. Our region has not experienced extensive deforestation, and half our land mass is still forested. It is helpful to appreciate what we have and why, and what we might lose if we don’t maintain our health ecosystems.
References:
How Trees Bring Water - https://www.youtube.com/watch?v=oY8ds4BiG1A&ab_channel=AndrewMillison
Includes an excellent 7 minute video.
Milan Milan: He Helped us Understand Rain, https://climatewaterproject.substack.com/p/millan-millan-he-helped-us-understand
What is the Biotic Pump - tps://www.thebioticpump.com/what-is-the-biotic-pump
Don’t miss the section on: Trees, technological marvels of nature - same website.
What is a Forest - A Comprehensive Ecosystem Review (scroll down midway), 10 very good paragraphs, Ali Bin Shahid, https://r3genesis.substack.com/p/87-what-is-a-forest-a-comprehensive
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