# Urban Overheating Impact: A Case Study on Building Energy Performance
## 3 Results and Discussion
### UHI in Rome: Climatic Data Comparison
Overall, Rome is distinguished by lower values than Fiumicino, except in a few moments in winter. Figure 4: Monthly wind velocity values recorded in Rome, Fiumicino and Ciampino. The decrease in urban temperatures is also due to the relative humidity that reduces the evapotranspiration effect. It is known that through evapotranspiration, areas consisting of water bodies, urban agriculture and vegetation can significantly contribute to microclimatic mitigation and therefore to environmental cooling [34]. Fiumicino, due to its position near the Tyrrhenian coast, has relatively higher humidity levels during the summer. In 2019, Rome recorded relative humidity values between 64.5% and 85.0%, while in 2020 the percentage range becomes equal to 63.8% and 82.5%, with an annual average of approximately 72.7%. In contrast, Fiumicino recorded annual average values of 73.7% in 2019 and 74% in 2020. Ciampino has the lowest relative humidity, with minimum and average values, respectively, equal to 54.9% and 66.6% in 2019 and 54.9% and 66.3% in 2020. In addition, similar trends and particularly comparable annual average values occur in the two years of monitoring, with percentage differences between 0% and 0.5%. It is worthwhile to notice that Fiumicino and Ciampino are not actually \"rural areas\" because they are surrounded by small buildings, albeit with a smaller average height and a different building density. Starting from the temperature data recorded by the climatic control units during the monitoring period, it was possible to determine the monthly Urban Heat Island Intensity (UHII). This index allows us to evaluate the UHI intensity. It was computed during the day and night, as specified in the Methodology section: for the diurnal UHI intensity, the average maximum temperatures measured in Rome and Fiumicino were used for the subtraction between the own values; for the nocturnal UHI intensity, the same operation was performed using the average minimum measured temperatures (Figure 6). The same procedure was performed comparing Rome and Ciampino (Figure 7). Comparing 2019 and 2020, the results in terms of UHII show significant differences between the night and day. While in 2019 the greatest differences were reached during the night, in 2020 greater diurnal values were identified. Analyzing the UHIIs obtained by the comparison between Rome and Fiumicino (Figure 6), in 2019 the maximum nocturnal value was equal to 3.77 \({}^{\circ}\)C, while the average annual day and night values were equal to 1.45 and 2.21 \({}^{\circ}\)C, respectively. In 2020, a different trend can be observed, with maximum differences in diurnal UHII (equal to 4.48 \({}^{\circ}\)C in June 2020), an average annual daytime value of 3.04 \({}^{\circ}\)C and a nocturnal value of 1.04 \({}^{\circ}\)C.  
Figure 5: Monthly relative humidity values recorded in Rome, Fiumicino and Ciampino. Furthermore, the percentage differences between the average values of UHII calculated in the two-year registration period are equal to 110%, referring to the day, and \(-52.8\%\), referring to the night. Similar trends, even if with different values, were also observed when comparing Rome and Ciampino (Figure 7). In this case, the maximum UHII was recorded at night, with a value of 2.87 \({}^{\circ}\)C (June 2019), while the average annual diurnal and nocturnal values are equal to 1.34 and 1.87 \({}^{\circ}\)C, respectively. On the other hand, in 2020, the maximum values of diurnal UHII (equal to 3.83 \({}^{\circ}\)C) can be observed during May 2020. The average annual diurnal UHII is equal to 2.79 \({}^{\circ}\)C and the average nocturnal value is 0.50 \({}^{\circ}\)C. Furthermore, the percentage differences between the average values of UHII calculated in the two-year registration period are equal to 108.4% in the daytime case and \(-73.4\%\) in the night case. Figure 6: UHII comparison of Rome and Fiumicino during the day and night. Figure 7: UHII comparison of Rome and Ciampino during the day and night.