Performance evaluation of green roofs in urban runoff reduction

Urbanism directly affects the hydrological cycle. One of the ways to manage runoffs in urban areas that is considered nowadays is green roof creation. Green roof is mainly created in humid and semi-humid areas, and efficiency of green roofs in arid and semi-arid areas has attracted less attention. In the current study, to evaluate the effect of green roof in arid and semi-arid to reduce runoff, an experimental green roof without vegetation was designed in Behbahan city of Khuzestan province in Iran. The city has an arid and semi-arid climate. Experimental Green roof was studied during 7 months. During the study, the data regarding the height of rainfall, soil moisture in different soil layers of the experimental green roof as well as the amount of output runoff were measured. The results showed that the amount of moisture in the surface layer of soil is severely affected by rainfall. The average surface soil moisture has been about 20.5 % and in the deep and middle layers has been 24.8 and 24.1, respectively. In addition, regarding runoff reduction and delays in creating runoff, the results showed that in the observed rain events, in average, 92.2 percent of volume of rainfall has been kept in soil, and has not been converted into runoff. Due to arid and semi-arid climate of the target area and high-intensity of rainfall, green roof can reduce a considerable percentage of runoff.