Metro-Tucson has sufficient local renewable water supplies to support roughly 1.6 million desert street trees and 1.3 million conventional fruit and nut trees. Street trees would use street runoff and must be located in and adjacent to the streets. Conventional food trees would rely on roof runoff and gray- and condensate-water and would be near houses.
In total, there are about 37KAF (1000 acre-feet) of harvestable street runoff and over 29KAF of graywater from residential areas. (Commercial areas and major roads produce a similar amount of runoff but present different issues and challenges, including water quality.)
The key is to plant trees where there is clean (enough) unused, free water. Otherwise, we will be using more groundwater at the very time the “well is running dry”. And low-income people and parts of town will not participate in the Mayor’s Million Tree Initiative, unless their increased water use is heavily subsidized. (Why do think poor areas have so few trees?)
Q: Where would we put a million more trees in neighborhoods throughout Tucson? And in ways that don’t use groundwater? A: In England, they’re called Home Zones. In Denmark – Woonerven. In Tucson, I suggest we call them Park Neighborhoods.
Home Zones (Park Neighborhoods) use extensive traffic calming (chicanes, traffic circles, diverters, and pocket parks) to slow traffic to pedestrian-safe speeds, and to create playgrounds, community gardens, and NH meeting places. We can shade them with thousands of rain- and gray-watered food trees.
The precise locations and approaches are critical for success. According to PAG, there are 82 square miles of pavement and 40 sq.mi. of roofs in metro-Tucson. If rain is harvested at the edge of the roof and road, approximately 80% can be captured and potentially used. If we allow it to flow from a mile before catching/storing it, only about 5%-10% of the same water can be harvested. There is enough unused, free water to support several million trees, if we use a distributed approach to create our future water supply.
This is sufficient renewable, local water to support the transformation of Tucson into a network of Park Neighborhoods, with local public art and places to play and meet, and where we can all live in an urban food forest that can produce millions of pounds of fresh, local food. (And hundreds of local jobs.)
Just one of the many options for our sustainable Tucson 2045.