We will expand the amount of green, permeable surfaces across the city to reduce storm water runoff
Green spaces act as natural storm water capture and retention devices. The 9,000 acres of vegetative cover lost between 1984 and 2002 could have absorbed, according to an analysis by the U.S. Forest Service and the City's Department of Parks & Recreation (DPR), 243 million gallons for every inch of rain. Trees capture rainfall on their leaves and branches and take up water through their roots, and release significant volumes to the air through evaporation. In all, the DPR estimates that city street trees capture 870 million gallons of stormwater each year. At least four million gallons of water are absorbed by soil around street trees during each storm event.

Over the next 25 years, we will undertake 40 new Greenstreets projects every planting season, bringing the citywide total to more than 3,000 by 2030. A one-acre Greenstreet can hold about 55,000 gallons of storm water. The existing total acreage of Greenstreets sites in New York City is almost 164 acres, which translates into nine million gallon capacity citywide. With an additional 40 new Greenstreet projects, covering 75 acres, the capacity to hold stormwater will increase by four million gallons.

In addition to increasing stormwater storage through Greenstreets, we will increase the number of trees in the city by one million. New designs for the tree pits could significantly increase this capacity as well.

Progress (as of 4/22/08):
See Open Space initiatives