Urban thermal variability from satellite and ground observations: a case study over Valencia (Spain)

As world mean temperature arises, the Urban Heat Island (UHI) phenomenon is intensifying in most cities worldwide and is frequently exacerbated by heatwave events. It directly affects citizens’ health, thermal comfort and daily activities. A detailed understanding of the spatial and temporal variability of the UHI is therefore increasingly necessary for urban planning and the development of heat mitigation strategies. UHI intensity is commonly evaluated using localized air temperature observations, which often provide limited spatial coverage of the urban area in the absence of a sufficiently extensive sensor network. In this context, thermal infrared (TIR) remote sensing data with high spatial and temporal resolution are considered as a valuable tool for assessing the urban thermal environment. Several studies have used satellite data to investigate Surface Urban Heat Island (SUHI) and to analyse urban thermal behaviour. However, the accuracy of satellite-derived measurements depends on observation geometry and the properties of surface endmembers within the satellite field of view, and these measurements can differ substantially from near-surface air temperature observations. Since the relationship between surface and near-surface temperatures remains insufficiently determined, it is essential to investigate the link between both variables to enhance the use of satellite data in urban climate studies.

In this work, the thermal variability of land surface temperature (LST) derived from Landsat 8 and 9 (30 m resampled spatial resolution) over the city of Valencia (Spain) is compared with near-surface air temperature observations from the VITUclim thermal sensor network. The VITUclim network comprises more than 80 thermohydrometer sensors distributed across the urban area of Valencia and represents one of the densest urban thermal monitoring networks in Europe. Sensors are installed at 3 m above ground level following a systematic deployment strategy to ensure observational consistency. This study represents the first application of VITUclim data for urban climate studies. Results reveal notable discrepancies between LST and air temperature, reaching up to 10 K during daytime conditions. Further analyses will be conducted to improve the understanding of the relationship between these two variables in the study area.