## 3 Results
### Spatial and Seasonal Variability of LST Trend
#### 3.2.1 Nighttime Trend  
All urban extents studied showed positive annual trends in nighttime LST (Table 4), with Delhi witnessing the highest change rate in 23 years (2.02 \({}^{\circ}\)C), followed by Surat (1.94 \({}^{\circ}\)C), Ahmedabad (1.90 \({}^{\circ}\)C), Lucknow (1.72 \({}^{\circ}\)C), Lahore (1.68 \({}^{\circ}\)C), and Karachi (1.60 \({}^{\circ}\)C). A bar chart showing the (a) annual and (b) seasonal (May-June-July, MJJ) total change in nighttime and daytime MODIS-derived LST over major cities for the period 2000-2023 is provided in Figure 8.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline
**Sl.** & **Cliy** & **Ann.** & **Jan** & **Feb** & **Mar** & **Apr** & **May** & **Jun** & **Jul** & **Aug** & **Sep** & **Oct** & **Nov** & **Dec** \\ \hline  
oimbatore & 1.17 & 1.45 & 0.74 & 1.90 & 2.15 & 1.00 & 1.07 & 2.29 & \(-\)0.41 & 0.70 & 1.06 & 1.10 & 2.15 \\ \hline
20. & Colombo & 0.83 & 0.99 & 0.67 & 0.07 & 1.58 & 0.43 & 0.87 & 1.00 & 1.25 & 1.29 & 0.51 & 0.53 & 1.05 \\ \hline \end{tabular} (Ann.: Annual).  
\end{table}
Table 4: Total change in nighttime temperature (LST, \({}^{\circ}\)C) based on the linear trend from 2000–2023.  
Figure 8: Bar chart showing the (**a**) annual and (**b**) seasonal (May–June–July, MJJ) total change in nighttime and daytime MODIS-derived LST over major Indian cities and surrounding other cities for the period 2000–2023.  
Nighttime LST showed an increasing trend in most parts of the country and surroundings with a total change of \(>\)3 \({}^{\circ}\)C in densely populated urban agglomerates during MJJ months (Figures 7 and 8). Based on the linear fit, it can be clearly observed from Figure 7 that the northern Indo-Gangetic flat plains (Delhi, Haryana, Uttar Pradesh, Jaipur) and western Kutch region (Gujarat) have undergone much higher warming (1-4 \({}^{\circ}\)C) in the past 23 years for the AMJ months than the rest of the study.  
Significant seasonal variations in the total change of nighttime LST over these cities were observed with the pre-monsoon (March-April-May) and monsoon (June-July) seasons (Figure 8b) showcasing an average higher sporadic pocket of warming except for Dhaka (\(-\)0.15 C\({}^{\circ}\)), while the winter season showed a relatively lesser warming trend.  
The total change in nighttime LST for April, May, and June are individually represented in Figure 9, which clearly depicts the effect of SUHI over urban cities. The linear trend of nighttime LST inside all the city limits was visibly much higher than the surrounding 10 km buffer zone for all months, while rural areas showed a negative or nil trend. There were spatial and seasonal variations in the linear trend of nighttime LST over Indian cities and surrounding cities. Apart from the cities marked in Figure 9, adjacent two and three-tier cities such as Amritsar, Jalandhar, Aligarh, Agra, Ludhiana, Meerut, and Bareilly in the northwestern plains of India could be identified as showing the SUHI effect visible in temporal trend analysis. Along the northwestern plains of India, June showed one of the highest total changes in warming nighttime LST, with Delhi exhibiting \(>\)4 \({}^{\circ}\)C change.  
Figure 9: _Cont._