An urban ecohydrological model to quantify the effect of vegetation on urban climate and hydrology (UT&C v1.0)

• Main Authors: MEILI, Naika, MANOLI, Gabriele, BURLANDO, Paolo, BOU-ZEID, Elie, CHOW, Winston T. L., COUTTS, Andrew M., DALY, Edoardo, NICE, Kerry A., ROTH, Matthias, TAPPER, Nigel J., VELASCO, Erik, VIVONI, Enrique R., FATICHI, Simone
• Format: text
• Language: English
• Published: Institutional Knowledge at Singapore Management University 2019
• Subjects: Environmental Sciences
• Online Access: https://ink.library.smu.edu.sg/soss_research/3043; https://ink.library.smu.edu.sg/context/soss_research/article/4300/viewcontent/gmd_2019_225_pvoa_cc_by.pdf
• Institution: Singapore Management University

Increasing urbanization is likely to intensify the urban heat island effect, decrease outdoor thermal comfort and enhance runoff generation in cities. Urban green spaces are often proposed as a mitigation strategy to counteract these adverse effects and many recent developments of urban climate models focus on the inclusion of green and blue infrastructure to inform urban planning. However, many models still lack the ability to account for different plant types and oversimplify the interactions between the built environment, vegetation, and hydrology. In this study, we present an urban ecohydrological model, Urban Tethys-Chloris (UT&C), that combines principles of ecosystem modelling with an urban canopy scheme accounting for the biophysical and ecophysiological characteristics of roof vegetation, ground vegetation and urban trees. UT&C is a fully coupled energy and water balance model that calculates 2 m air temperature, 2 m humidity, and surface temperatures based on the infinite urban canyon approach. It further calculates all urban hydrological fluxes, including transpiration as a function of plant photosynthesis. Hence, UT&C accounts for the effects of different plant types on the urban climate and hydrology, as well as the effects of the urban environment on plant well-being and performance. UT&C performs well when compared against energy flux measurements of eddy covariance towers located in three cities in different climates (Singapore, Melbourne, Phoenix). A sensitivity analysis, performed as a proof of concept for the city of Singapore, shows a mean decrease in 2 m air temperature of 1.1 ◦C for fully grass covered ground, 0.2 ◦C for high values of leaf area index (LAI), and 0.3 ◦C for high values of Vc,max (an expression of photosynthetic activity). These reductions in temperature were combined with a simultaneous increase in relative humidity by 6.5 %, 2.1 %, and 1.6 %, for fully grass covered ground, high values of LAI, and high values of Vc,max, respectively. Furthermore, the increase of pervious vegetated ground is able to significantly reduce surface runoff. These results show that urban greening can lead to a decrease in urban air temperature and surface runoff, but this effect is limited in cities characterized by a hot, humid climate.