Dual Potential of Garden Rooftop Farms for Heat Island Mitigation and Spatial Productivity

Abstract

The Garden Rooftop Farm (GRF) development is not just about planting rooftops, but a significant expansion and upgrade of ground-level activity spaces. This paper examines the GRF development potential based on urban heat island (HUI) mitigation and urban spatial productivity (USP) level. First, the evaluation indicators and quantification methods for HUI mitigation and USP level are provided. Then, based on the microclimate field measurements of typical GRFs during the summer high temperature period, the time-dependent characteristics of UHI mitigation are analyzed and the mechanism is explained. Finally, the spatiotemporal heterogeneity matrix of the USP level is constructed and the mechanism analysis including USP time distribution, thermal stress redundancy and microclimate effects is carried out. The results showed that the maximum daily average UHI mitigation was 1.25°C in a typical summer month and up to 1.75°C in the early night. The higher evapotranspiration and lower heat retention of GRF were the main reasons for the above advantages. The spatiotemporal heterogeneity of USP levels in single-theme development scenarios is highly significant. Among the 208 assessment scenarios for four weather types, the proportion reaching Level II fell from 95.23% to 14.29%. In contrast, the compound function scenario generally had lower USP levels, with an average of 46.88% of cases falling below Level IV. The results confirm that the development and targeted design of GRFs on unused urban rooftops contributes to urban cooling, while the USP assessment represents a further exploration of the practical application value of UHI mitigation benefits.

Keywords: Garden rooftop farms, Green infrastructure, urban heat island, Spatial productivity, Spatiotemporal heterogeneity