A near real-time CO₂ mapping web application for the Mediterranean city, Heraklion, Crete.

Mediterranean urban regions are increasingly exposed to extreme warm conditions, associated with the effects of climate change. Thus, continuous monitoring of environmental variables, such as temperature and CO₂, is essential for assessing sustainability within urban infrastructures. This study presents a web-application that employs the Surface Urban Energy and Water Balance Scheme (SUEWS) model, an interface simulating urban environmental dynamics, for the city of Heraklion, Greece. Based on near-real time and high-resolution maps of air temperature, energy and CO₂ fluxes, the web-application offers user-friendly tools, which enable timeseries analysis of CO₂ sources/sinks and urban heat islands in user-specified regions. Among its functionalities, the application offers time-series analysis and statistical tools to monitor impact of changes in urban structure and evaluate mitigation strategy scenarios like nature base solutions. Model was evaluated in quarterly diurnal patterns for 2022, using flux tower observations at two locations in Heraklion: the first (HECKOR) at the central business district, where traffic dominates CO₂ emissions; and the second (HECMAS) in a residential area, where building emissions are significant. Both towers are labeled by ICOS (Integrated Carbon Observation System). Results indicated lower uncertainties in CO₂ flux estimated by SUEWS in the residential area, where building emissions exceed those from traffic (HECMAS), compared to a central business district, where traffic dominates CO₂ emissions (HECKOR). Inaccuracies in both case studies were identified due to the absence of near-real-time traffic and human activity data (RMSE ≤ 6.3 µmol m⁻² s⁻¹). The effect of photosynthesis on total carbon fluxes was minimal in the city center due to the low vegetation fraction, while in HECMAS the results display the carbon sequestration effect of vegetation. Through its capability for dynamic monitoring multiple spatial scales—ranging from individual building blocks to entire neighborhoods and cities—the application holds significant potential for supporting climate-sensitive urban planning and policymaking.