Berlin Evapotranspiration and Cooling Services

Abstract

Evapotranspiration (ET) is an essential variable for assessing water balance and the urban heat island (UHI) effect. ET is deeply dependent on the land cover as it derives mainly from soil evaporation and plant transpiration. The model soil-canopy observation of photosynthesis and energy fluxes (SCOPE) accounts for a broad range of surface-atmosphere interactions to predict ET. However, like most modelling approaches, SCOPE assumes a homogeneous vegetated landscape to estimate ET. As urban environments are highly fragmented, exhibiting a mix of vegetated and impervious surfaces, we propose a two-stage modelling approach to capture most of the spatiotemporal variability of ET without making the model overly complex. After predicting ET using the SCOPE model, the bias caused by the assumption of homogeneous vegetation is corrected using a vegetation fraction map. The ET prediction accuracy was assessed using eddy covariance towers, showing an R2 of 0.84 for the residential-vegetated site and 0.57 for the built-up site in Berlin during 2019. Urban green infrastructures (UGI) are fundamental to microclimate regulation and thermal comfort through evapotranspiration (ET) and shading services. High-spatiotemporal-resolution ET maps are required to plan and manage UGI to mitigate the UHI and droughts. We developed a method using open-access data, including hourly meteorological data and remote sensing vegetation parameters. A greening cooling service index (GCoS), divided into evapotranspirative (ECoS) and radiative (RCoS) cooling effects were mapped for the entire Berlin, Germany.