Cropping in Urban Ecosystems

Abstract

The thesis investigates the role played by green roofs in urban areas by reviewing the existing literature and by developing a numerical platform. For this purpose, the FAO-56 dual crop coefficient method (FAO-56 method) has been adopted to evaluate evapotranspiration taking place in some green infrastructure (GI) practices, i.e. green roofs. The Tew Extension was incorporated into the FAO-56 method to achieve more accurate estimates. Modifications were also made to the FAO-56 method with the Tew Extension for the application to agricultural green roofs. The findings relating to the test green roofs’ functions of annual rainfall retention, peak flow rate reduction and runoff delay reveal that green roofs can greatly help mitigate urban runoff volume and rate problems. Regarding the impact on runoff quality, the test green roofs, in most cases, deteriorated the incoming water. The FAO-56 method was applied to urban agriculture and agricultural green roofs, based on which evapotranspiration and irrigation needs of the ten annual crops grown in fields and on rooftops in Australia’s five major cities were estimated. In both field and rooftop cases, different crops planted in the same city resulted in significantly different irrigation needs. In all five cities, all the crops grown on rooftops evapotranspired more water than the crops grown in fields. Nearly in all cases, crops grown on rooftops demanded more irrigation than these crops grown in fields. Most of the water lost through evapotranspiration was transpiration in both field and rooftop cases; however, the percentages of transpiration to evapotranspiration on rooftops were smaller when compared with these in the field case for all the crops in all five cites. In general, a city that is more irrigation water dependent is likely to use a larger portion of total water beneficially. Crops grown on rooftops are likely to take up smaller portions of total delivered water than the same crops grown in fields.