## 3 Results
### Heatwave Detection and Measurement  
#### 3.2.1 Ground-Observed Air Temperature Heatwave  
Our analysis of annual mean air temperature heatwave indices, considering both \(T_{\text{max}}\) and \(T_{\text{min}}\) heatwaves, reveals distinct patterns across different areas. In urban settings, the average yearly occurrence of daytime \(T_{\text{air}}\) heatwaves ranges between 3.4 and 4.2 days,  
Figure 3: Importance of selected variables to predict LST for daytime **(a,b)** and nighttime **(c,d)**.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Statistical** & **MOD11A1\_day** & **MYD11A1\_day** & **MOD11A1\_night** & **MYD11A1\_night** \\
**Measures** & **(C/V)** & **(C/V)** & **(C/V)** & **(C/V)** \\ \hline \(R^{2}\) & 0.50/0.45 & 0.51/0.29 & 0.55/0.64 & 0.64/0.48 \\ RMSE & 2.64/3.79 & 2.79/5.02 & 2.03/2.09 & 1.79/2.57 \\ Min Interval & 2.52/3.79 & 2.66/5.02 & 1.92/2.08 & 1.69/2.57 \\ Max Interval & 2.75/3.79 & 2.92/5.03 & 2.13/2.09 & 1.89/2.51 \\ MAE & 2.02/2.95 & 2.15/3.88 & 1.48/1.61 & 1.33/1.94 \\ MBE & \(-0.05/-0.41\) & \(-0.08/-0.58\) & 0.00/0.05 & 0.19/ –0.21 \\ \hline \hline \end{tabular} Note: C is Calibration, V is Validation.  
\end{table}
Table 3: Evaluation of calibrated and validated land surface temperature predictions.  
compared to 5.2 to 6.8 days in peri-urban regions, and 3.6 to 4.0 days in rural locales. Notably, the highest frequency of HWF is observed in urban areas at 15.0 to 16.7 days per year, escalating to 26.4 to 27.1 days in peri-urban regions and 16.9 to 21.0 days in rural environments. The HWD extends to 4.5 to 5.0 days per year in urban centers, 5.5 to 6.0 days in peri-urban zones, and 5.9 to 6.5 days in rural areas. \(T_{\rm air}\) heatwave analysis reveals that the highest HWM in urban regions falls between 35.8 and 36.7 \({}^{\circ}\)C, 35.5 and 36.8 \({}^{\circ}\)C in the peri-urban area, and 34.3 and 37.6 \({}^{\circ}\)C in the rural area. The peak air temperatures of the HWA are recorded at 37.5-37.9 \({}^{\circ}\)C in urban areas, 37.6-38.1 \({}^{\circ}\)C in peri-urban zones, and 36.4-39.7 \({}^{\circ}\)C in rural settings. Consequently, the peri-urban area of Pathum Thani is distinguished by having the most significant occurrence of daytime heatwaves. Moreover, urban locales, especially Bangkok, persistently display the highest rates and lengths of heatwave events, and this trend has been progressively intensifying over the years. This observation highlights the critical need for focused climate adaptation strategies in these areas to mitigate the impacts of increasing heatwave activity.  
Regarding nighttime \(T_{\rm air}\) heatwaves, the number of HWN in urban areas ranges from 3.0 to 3.5 days per year, paralleling the daytime patterns observed in other regions. Urban areas witness the maximum HWF, with 12.3 to 15.5 days per year, surpassing the 18.8 to 22.5 days in peri-urban regions and the 3.6 to 14.3 days in rural areas. For the longest HWD, it extends from 3.3 to 13.5 days per year in urban settings, 4.6 to 5.4 days in peri-urban areas, and 3.8 to 5.0 days in rural landscapes. The average cumulative HWM in urban locales is recorded between 35.8 and 36.7 \({}^{\circ}\)C, significantly higher than the 26.3-27.1 \({}^{\circ}\)C in peri-urban areas and 23.7-26.3 \({}^{\circ}\)C in rural settings. The peak air temperatures for the HWA reach 28.5-29.3 \({}^{\circ}\)C in urban areas, 27.8-28.8 \({}^{\circ}\)C in peri-urban zones, and 25.6-27.4 \({}^{\circ}\)C in rural environments. Thus, nighttime \(T_{\rm air}\) heatwave patterns exhibit similarities to their daytime counterparts, with urban regions being particularly prone to more frequent and severe events.