Impact of drought on cooling capacity and carbon sequestration in urban green area

Abstract

Through experimental observations of carbon and energy exchange in Urban Green Areas (UGA) using the Eddy Covariance technique we show that the vegetation air cooling capacity and carbon uptake are influenced by water availability: multivariate analysis shows that solar radiation (Rg) was the primary control factor in latent heat (LE) and CO2 fluxes followed by the air temperature (Tair) and Vapor pressure deficit (VPD). The relative importance of VPD was higher in correspondence of the year characterized by drought condition. The mature UGA investigated was a net carbon sink only during the summer season from June to September while on annual basis was a carbon source for all the years investigated. The summer average daytime UGA air temperature cooling potential ranged from 3.02 °C (± 1.4) during the wet season, to 2.1 °C (± 1.3) during the dry season. The city-scale application of the i-Tree model highlighted the reduced cooling potential effect of the UGA during dry periods, relative to those with better soil water supply from precipitation and indicates that, in case an emergency irrigation would be possible, about 50 L m−2 during the drought period would compensate the water shortage.