Potential of urban rooftop agriculture as a climate change adaptation tool through efficient water mangement

Abstract

Urban cities are facing the challenges of microclimatic changes with substantially warmer environments than adjacent rural areas and making cities uncomfortable embracing challenges like ecological imbalances, fresh food unavailability, water insecurity, insufficient agricultural land, increased climate change risks, reduced green spaces and many other. Resilient cities through green approaches are the global demand to eliminate the climate change impacts. The gradual growth of urban rooftop agriculture (URTA) is an increasing trend among private residents towards the green cities and URTA differs substantiallyfromtraditionalagricultureintermsofbuilt-upurbanenvironment.So,URTA needed a science-based study to achieve economically, socially and ecologically viable urban agriculture with indicative guidelines to popularizeit.

For this purpose, this study was carried out two experimental plots with agriculture on roof of the buildings in Dhaka. The area covered with agriculture was 70% of the roof top area where selected crops were tomato, brinjal, chili, bottle gourd and leafy vegetables. The modern drip method was considered as an irrigation technique. The water productivity of those crops was compared to the traditional irrigation approach. So, groundwater and grey andrainwaterwereconsideredasirrigationsource.ET0ofthosecropswereestimatedusing the CROPWAT 8.0 model. The microclimatic parameters like air temperature, near roof surface temperature, indoor temperature and relative humidity and carbon dioxide concentrationfromdifferentlocationsoftheexperimentalagriculturalplotandfromnearby bare roofs were recorded. Five private rooftop gardens with green area coverage of 40%, 50%, 60%, 80%, and 85% and nearby 5 bare roofs were also selected and measured the temperature in the roofs and rooms below the roofs for estimating cooling effect of rooftop agriculture. Questionnaire surveys were done for 200 private rooftop gardens for understanding the social dynamics of the existing private rooftopgardens.

The results showed that the temperature in the rooftops and top floor rooms under rooftops werefoundtobereducedfrom1.2°Cto5.5°Cand1.38to3.07°Crespectively.Thecooling load was found to be decreased from 3.62% to 23.73%, and energy saving increased significantly from 5.87% to 55.63% for agricultural roofs compared to bare roofs. Excess irrigation water use by the traditional method was around 30% to 75% of compared to the dripirrigationmethod.Itwasfoundthatdripirrigationusingrainandgrey-watercouldsave up to 80% potable water through increased yield by about 31.87% to 33.33% compared to handirrigationbyhosepipeorotherdevices.Basedontheexperimentalresultsofthestudy, a climate and water smart rooftop agricultural conceptual model (CWSRAM) has been proposed for further wide application of the urban rooftop agriculture to arrest urban heat islandandmicroclimaticparametersasatoolofclimatechangeadaptationtechnology.This conceptualmodelincludedtheneedforcapacitydevelopmentofdifferentactorsinnational rooftop agricultural systems and the provision of appropriate incentives to involve the private sector in strengthening rooftop agriculture as commercialthinking.

Itcouldbeconcludedthattheurbanrooftopagricultureishighlyenvironmentandeconomic friendly to compensate warming up of urban cities through cooling effect as well as supplying fresh vegetables to the dining tables. The city corporations, govt. agencies need tosupporttherooftopagricultureinitiativesthroughpolicysupportsandadditionofchange in building code. Findings of the study can be useful for urban planners, city dwellers, and researchers for their respective uses. The CWSRAM can serve as a guiding tool to achieve the resilient urban cities towards thesustainability.