## 4 Discussion
Karachi, Bengaluru, Hyderabad, Pune, and Jaipur showed highly contrasting diurnal behaviors with a negative daytime SUHI effect and a positive nighttime SUHI effect in both seasons. Delhi, Mumbai, Ahmedabad, and Kanpur showed daytime negative SUHI during pre-monsoon to onset of monsoon months, and positive SUHI during winter. Cities such as Colombo, Yangon, Lucknow, Kolkata, Dhaka, Lahore, Faisalabad, Surat, and Dhanbad showed positive SUHI during daytime and nighttime in both seasons. The daytime SUHI observations for Delhi, Kolkata, Lahore, Lucknow, Faisalabad, Jaipur, and Kanpur showed the highest peak during March, gradually decreasing during April-May-June-July, and peaking again during post-monsoon months. Mumbai, Bengaluru, Chennai, Hyderabad, Ahmedabad, Surat, Pune, and Coimbatore were observed to have the highest daytime SUHI effect during post-monsoon months and a relatively lesser peak during winter months. The daytime SUHI showed a much more complex pattern over the months compared with nighttime SUHI for all cities. Figure 12a,b shows the variability of nighttime and daytime SUHI over the studied cities. In India, Jaipur exhibited the highest nighttime SUHI during pre-monsoon to onset of monsoon (2.17 \({}^{\circ}\)C) months and during winter (2.63 \({}^{\circ}\)C). Similarly in Pakistan, Lahore showed higher nighttime SUHI during AMJ months than in Faisalabad and Karachi. It is noted that the nighttime SUHI effect was more pronounced than the daytime SUHI effect for all cities in and surrounding India except Colombo, as depicted in Figure 13. The  
Figure 12: Boxplot showing the variability of (**a**) nighttime and (**b**) daytime SUHI effect over selected major Indian cities for the period 2000–2023. highest nighttime SUHI exhibited by Delhi was during March and April (2.51 \({}^{\circ}\)C), and the lowest nighttime SUHI was during August. Lucknow and Kanpur are two closely located cities which exhibit anomalous seasonal daytime SUHI characteristics. Lucknow behaved as an urban heat island during AMJ months with an intensity of 0.36 \({}^{\circ}\)C (Figure 13). It is interesting to note that Karachi and Jaipur, having similar desert to semi-arid climate classification, show daytime negative SUHI effect in almost all months, which points out that the surrounding non-urban areas of these cities are warmer than the city core for all months. Both cities show a similar daytime urban cool island (UCI) effect in winter months (\(-0.52\) to \(-0.53\) \({}^{\circ}\)C), while during pre-monsoon to onset of monsoon, Jaipur shows much higher daytime negative UHI effect (\(-1.48\) \({}^{\circ}\)C) compared with Karachi (\(-0.49\) \({}^{\circ}\)C). This result agrees with the earlier literature that observed a significant role of thermal admittance of rural areas in creating a heat island effect. As the thermal admittance values of moist soil are similar to those of typical dense urban building materials, the temperature ranges within the urban area are comparable to those outside it, resulting in a low SUHI intensity. Nevertheless, during nighttime, rural areas have slightly lower temperatures compared with urban areas, indicating a positive SUHI [88]. The coastal setting of Karachi compared with inland Jaipur might also influence the more moderate heat island effect in Karachi than Jaipur. Dhaka, Kolkata, Faisalabad, Lahore, Dhanbad, Lucknow, and Surat showed positive daytime SUHI for almost all months compared with other cities which showed seasonal positive and negative daytime SUHI. Delhi, Kanpur, and Ahmedabad showed similar seasonal variation in daytime UHI with formation of cool islands or negative SUHI during pre-monsoon, monsoon and November-December months. The average daytime temperature and SUHI intensity patterns across all months of the year of inland cities, and coastal to near coastal cities, are depicted in Figure 11,b and Figure 11,d, respectively.