Washingtonians should take note of Chicago's initiative to plant rooftop gardens to help reduce summer temperatures in the Windy City [news story, Dec. 4]. Rooftop gardens in the District would offer a double benefit: They would contribute to cooler summers and they would also absorb water during rainstorms, water that would otherwise enter the stormwater drains.

In the portion of the District between Rock Creek and the Anacostia, stormwater mixes with sewer water before reaching the Blue Plains treatment plant. Even relatively light rains can overtax the system, leading to the discharge of the untreated mixture into the Anacostia River, Rock Creek and the Potomac via a system of 60 overflow pipes.

The discharge level has been averaging more than 1 billion gallons per year to the Anacostia River alone and is the main reason the Anacostia ranks among the 10 most polluted rivers in the country.

Buildings that absorb rainwater would reduce the load on the sewer system and deserve our support. The mayor, the D.C. Council and the D.C. Water and Sewer Authority might consider offering financial incentives for owners to add rooftop gardens to their buildings and for builders to design rooftop gardens into new projects.

The new Convention Center has extraordinary potential as a site for a rooftop garden. Given its size, its roof could accommodate a multiple-acre community vegetable garden and have room left for an athletic field. These green spaces are sorely needed by the Shaw residents who will live in the Convention Center's shadow.