Tag Archives: sustainability

urban jungles

a study published recently in Global Change Biology found that rainforests have been displaced as ecosystems that store the most carbon- by cities! cities store more carbon in their trees, buildings and dirt, than the densest and most productive tropical rainforests.

according to researcher Galina Churikina, who led the study, US cities store about 20 billion tons of organic carbon. most of this carbon is held in soils, though a sizable fraction is also contained within buildings constructed with wood. ironically, the key to city’s’ remarkable capacity to store carbon seems to be their artificial nature. buildings and asphalt “bury” soils, locking away carbon that was once part of a dynamic forest, grassland, or other natural ecosystem.

Shanghai, one of the world's largest cities, is an enormous carbon sink!

this is not to discount the importance of urban trees in both storing carbon and providing numerous ecosystem services. trees and other urban plants ameliorate temperatures, providing a cooling effect in summers that reduces the need for air conditioning. trees also directly take up CO2 emitted from cars, reducing the amount of pollution that enters the atmosphere from cities in the first place.

Urban trees such as those in Central Park, NYC, keep buildings cool, capture CO2, reduce stormwater runoff, and improve quality of life.

fog harvesting for a thirstier world

With droughts becoming more frequent and severe globally, people across the world have been finding creative ways to get a little more water. The residents of Lima, Peru, have long long struggled with a scarcity of fresh water. Bordering the inhospitably dry Atacames desert, Lima recieves a scant 1.5 cm of rainfall annually. Lima’s main fresh water source is glacial runoff from the high Andes during the spring and summer. Unfortunately, Andean glaciers are rapidly disappearing due to climate warming, and Peruvians are struggling to adapt to a future of even more severe water shortage.

The people of Lima do, however, have a plentiful supply of one form of water- fog. Fog sweeps up the South American coast from the Southern Pacific Ocean and rolls over the slopes of Lima year round. In the rural villages surrounding Lima, fog harvesting has been used by farmers for thousands of years. Cæsalpinia spinosa , commonly known as the Tara tree, is a small, shurb-like tree native to Peru that has evolved to survive in this arid environment by literally sucking water out of the air. Excess water that the Tara trees do not use runs off the trees and replenishes groundwater that has been lost due to years of drought. It also provides a convenient source of fresh drinking water for locals.

Gaia Vince reported for Science last month from a shantytown just outside Lima that has decided to scale up and modernize this age-old technique. On the tops of sand dunes, residents have constructed a series of 4 meter high mesh nets for trapping fog water. These nets are stretched  taught and faced perpendicular to the prevailing wind. As tiny fog droplets stick to the nets, they clump together and form large drops, which are collected as runoff by the bucketful. In conjunction with fog harvesting nets, locals have planted saplings that will soon be large enough to trap water themselves. This system has already been successful enough that nearby villages have set up similar projects. In the future, fog harvesting forests could provide Peruvian communities with an entirely self-sustaining means of obtaining water.

If you’re interested in learning more about fog harvesting, you can check out http://www.fogquest.org/ , a nonprofit organization devoted  implementing fog harvesting projects for rural communities.