# Evaluation of the Urban Weather Generator on the City of Toulouse (France)
## 3 Experimental Results
### Impact of the Rural Station  
As described in Section 2.2, UWB needs information issued from a rural station (to obtain the climatic context outside the city). These meteorological data include radiative fluxes and soil temperature. As shown in [30], this reference weather station impacts the quality of the estimation and it is then important to select the most adapted one. We then analyze, on the selected two pairs of days, the accuracy of UWB estimations in Carmes station for the three selected rural stations (Meteopole, Mondouzil, and Centre equestre, see Section 2.2.2). In Figures 4-6 are depicted, for Meteopole, Mondouzil, and Centre equestre:  
* The temperature at the rural station (dashed green);
* The simulated temperature for Carmes with UWB (yellow);
* The measured temperature in Carmes station (blue). Quantitative values of associated RMSE and MBE are visible in Table 6. As shown in Figures 4-6, there is an overall good agreement between the simulated air temperature and the values measured at Carmes station. However, the RMSE and MBE, ranging, respectively, from 1.73 \({}^{\circ}\)C to 3.48 \({}^{\circ}\)C and \(-2.24\)\({}^{\circ}\)C to 0.02 \({}^{\circ}\)C, show that the estimation accuracy varies according to the rural station. We observe in all cases, an overprediction of the air temperature starting in the middle of the night until early morning followed by a slight underprediction until sunset. In addition, abnormal peaks occur around 4 a.m. (which corresponds to the sunrise UTC hour) and this is regardless of the rural station used for the simulation. In one paper [30], the authors, explain these peaks: they occur during the night-day and day-night transitions as the underlying UBL submodel inside UWB relies on two different sets of equations (before and after the transition). According to [30], these discontinuities are reduced by the thermal inertia of the UBL air and can be attenuated by slightly modifying the shifting times between night and day. Figure 4: **Comparison of UWB air temperature simulations with measured on sunny and hot days in August 2020 at (Carmes) station, using (Meteopole) as a rural reference station. (a) 5 and 6 August 2020. (b) 19 and 20 August 2020. **  
Figure 5: **Comparison of UWB air temperature simulations measured on sunny and hot days in August 2020 at (Carmes) station, using (Mondouzil) as a rural reference station. (a) 5 and 6 August 2020. (b) 19 and 20 August 2020. **Even if the Meteopole station is located closer to the city in a less rural environment, the simulated air temperature based on this station fits slightly better the measurements of Carmes station based on rural station Meteopole than the one simulated based on Monodouzil station, with an MBE of \(-2.22\) \({}^{\circ}\)C and \(-2.24\) \({}^{\circ}\)C and RMSE of 3.39 \({}^{\circ}\)C and 3.48 \({}^{\circ}\)C, respectively, (Table 6). Simulations based on rural data from Centre equestre station stick the best to measured values (Figure 6) with an MBE of 0.02 \({}^{\circ}\)C and an RMSE of 1.73 \({}^{\circ}\)C (Table 6). The absence of anomaly peaks in the simulated air temperatures for Carmes, Meteopole, and Centre equestre rural stations on the 20 th of August can be explained by the fact that the night before was the hottest of the studied period (minimum 22 \({}^{\circ}\)C). Therefore, there is a low difference between the rural and in-city air temperature values for this specific day (e.g., the meteorological conditions may not been entirely favorable to UHI). Of course, this point would require further investigation. In the following results, the anomalies have been filtered out and linearly interpolated, as also suggested in [58]. With these corrections, it is even more obvious in Figure 7 that the simulated air temperatures at the Carmes station, based on Centre equestre rural station, have the lowest error along the studied period. In addition, these results highlight the importance of the choice of the rural station for UWG to accurately simulate air temperatures.