Measuring the urban heat island of Rome through a dense weather station network and remote sensing imperviousness data

The objective of this work is to characterize the summer urban heat island (UHI) of Rome (Italy) through a dense weather station network, consisting of 17 units. Measurements were collected in summers 2019-2020. We used a recent approach for calculating the UHI intensity, which relates air temperature to imperviousness (IMP) satellite measurements. To asses the reliability of this method we made a comparison with a LCZ-based approach, finding compatible daily trends of UHI intensity with a fixed bias during night. The correlation coefficients between IMP and daily maximum, minimum and mean temperatures were 0.17, 0.81 and 0.82, respectively, reflecting the nighttime UHI peak observed in other cities. The UHI intensity diurnal cycle pattern showed, starting from its minimum of -0.1 °C at 10:00 (CET), a progressive increase which intensifies after sunset reaching a maximum of 3.4 °C at midnight, followed by a slight decrease which exacerbates after sunrise. We found no relevant correlation between UHI and heat waves.