Exploring Rooftop Rainwater Harvesting Potential for Food Production in Urban Areas

Abstract

Homegrown fruits and vegetables are gaining popularity in many metropolitan areas with several facets connected to the wider urban agriculture phenomenon. At the same time, the relationship between urban food production and irrigation water is pivotal in terms of resource management. In this paper, we investigated water savings through the collection and use of harvestable rainwater from buildings' rooftops to irrigate 2631 fruits and vegetables gardens in the urban area of Rome (Italy). The methodology makes use of existing geospatial data and data derived from satellite image classification to estimate food gardens' irrigation requirements and harvestable rainwater from nearby buildings' rooftops. The comparison of the annual harvestable rainwater with irrigation needs allowed for computing the proportion of water self-sufficient gardens as well as the amount of gardens whose water needs might be partially fulfilled with rainwater. Statistics were produced by land use type (horticulture, mixed crops, olive groves, orchards, and vineyards) and under the hypothesis that irrigation systems with low and high field application efficiency might be employed. We found that 19% and 33% of the gardens could be water self-sufficient for the low and high irrigation efficiency scenario, respectively. The remaining gardens, by using the available rainwater, could satisfy 22% (low efficiency) and 44% (high efficiency) of the water needs resulting in a reduction in the use of conventional water sources.

Expanding the Distributed Generation Concept: Toward Decentralized Energy and Water Supply

“…The old approach is replaced by a new view in which rainwater is a valuable resource to be collected near where it has fallen via a simple collection system part of the built environment, using the resulting water near the collection site . In general, the yearly amount of harvestable rainwater RH is given by Equation where A catch (in m 2 ) is the surface area of the built environment (courtyards, rooftop, road, greenhouse, skylight, etc.) used to catch rainwater, P tot is the total annual precipitation (in m), and C is the dimensionless runoff coefficient, namely, the efficiency of the harvesting system, whose value depends on both climatic and architectural factors varying between 0.6 (heavy rain and leaks, with gutters overflowing) and 0.95 (system is in perfect condition, no leaks and gentle rain) .…”

“…used to catch rainwater, P tot is the total annual precipitation (in m), and C is the dimensionless runoff coefficient, namely, the efficiency of the harvesting system, whose value depends on both climatic and architectural factors varying between 0.6 (heavy rain and leaks, with gutters overflowing) and 0.95 (system is in perfect condition, no leaks and gentle rain) . The overall amount of rainwater potentially intercepted and collected by rooftops in a certain urban area, for example, can be estimated by considering the overall rooftop size and the yearly average precipitation values from historic data …”

“…The old approach is replaced by a new view in which rainwater is a valuable resource to be collected near where it has fallen via a simple collection system part of the built environment, using the resulting water near the collection site. [3,8] In general, the yearly amount of harvestable rainwater RH is given by Equation (1) [13] RH tot catch…”

“…Even in Brazil, scholars lately published the first guidelines aimed at government to deploy policies to incentivize rainwater catchment systems; whereas in Texas, the State's water agency awards annually the three best rainwater harvesting projects in residential, commercial/industrial, and educational/governmental categories since 2007 . In Mediterranean countries, recent efforts toward rainwater harvesting include its use as a control option to reduce runoff peaks, as well as the use of harvested rainwater in urban agriculture for food production …”

“…[11] In Mediterranean countries, recent efforts toward rainwater harvesting include its use as a control option to reduce runoff peaks, [12] as well as the use of harvested rainwater in urban agriculture for food production. [13] Even though in some countries (for example, the plumbing code in the United States) the law does not allow indoor use of harvested rainwater, scholars in the US recently found that rainwater harvesting could cover >50% of the domestic water Rainwater harvesting decentralizes the water supply in full analogy to what building-integrated photovoltaics and solar thermal do for electricity and heat. In this new decentralized generation scenario, the built environment is used to collect both sunlight photons and water molecules with significant economic and environmental benefits.…”