The effect of low impact development facilities on evapotranspiration in an outdoor space of urban buildings

Abstract

Low impact development (LID) facilities have been regarded to have important regulatory effects on urban evapotranspiration (ET). However, due to the influences of heterogeneity of underlying surfaces or facilities, solar radiation, building shading and rainfall conditions, the ET variations in outdoor space of urban buildings (OSUB) with various LID facilities are complex and have not been reported. In this paper, a three-temperature model (so called 3T model) combining with a portable thermal infrared imaging sensor was used to in-situ measure the ET rates of different LID facilities and traditional underlying surfaces of an OSUB in 2019 in Shenzhen, China. Specifically, the seasonal, daily and diurnal variations of ET in the OSUB and their influencing factors were investigated. The results indicate that (1) the LID facilities have higher ET rates than the traditional surfaces in wet seasons; the ET rates of bioretention (BR-H), vegetated swale (VS-Z) and permeable concrete pavement (PCP) are 38%, 18% and 250% higher than those of traditional garden (TG-H), lawn (TL-Z) and impermeable brick pavement (IBP), respectively, in this study; (2) the diurnal variation of ET is greatly affected by solar radiation intensity, building shadow and moisture inside the LID facilities; and the ET increase by LID is higher in the OSUB with higher solar radiation and no shadow; (3) vegetated LID facilities (e.g., BR-H and VS-Z) can maintain at a relatively high ET rate for a longer period after rain than the non-vegetated LID facilities (e.g., PCP), indicating a stronger ability to increase urban ET; (4) when the proportion of LID in OSUBs increases from 0% to 50% and 100%, the ET rate of OSUBs increases by 28% and 51% respectively, and the annual ET of built-up areas in Shenzhen increases by 6.58 mm and 11.41 mm respectively. The effects of soil media, vegetative cover, LID facility structure, local climate and building shadow on the ET of OSUBs should be considered for extrapolating the site-scale study to urban or catchment scale.