# Spatiotemporal Variation of Land Surface Temperature Retrieved from FY-3D MERSI-II Data in Pakistan
## 4 Results
### Spatial Distribution of Seasonal LST and Trend Analysis  
The spatial distribution of the seasonal mean LST rises with decreasing latitude, similar to the yearly mean LST, with low values in the northern and high values in the southern regions of the country. However, there are differences between each seasonal dataset. Because the Earth's axis is tilted relative to the orbital plane, the solar elevation angle fluctuates throughout the year, making winter cold and summer hot. To further reveal the LST changes, seasonal means were processed from the daily averages of the LST data to calculate the trend analysis through the MK test, along with the slope (Table 3). Based on the classification of the four seasons throughout the study region, seasonal variation has an important effect on LST across Pakistan. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Region**} & \multicolumn{3}{c}{**MK Z-Score**} & \multicolumn{2}{c}{**Slope**} \\ \cline{2-5}  & **Min** & **Max** & **Mean** & **(\({}^{\circ}\)C/Year)** & \multirow{2}{*}{_p_**-Value**} \\ \hline I & \(-\)4.97 & 3.57 & \(-\)1.86 ** & \(-\)0.013 & 0.05 \\ \hline II & \(-\)3.97 & 3.14 & 0.23 & 0.003 & 0.63 \\ \hline III & \(-\)3.28 & 3.58 & 0.23 & 0.003 & 0.61 \\ \hline IV & \(-\)3.39 & 3.51 & 0.07 & 0.001 & 0.71 \\ \hline V & \(-\)2.25 & 3.96 & 2.10 * & 0.019 & 0.10 \\ \hline \hline \end{tabular} Note: Where \({}^{***}\) and \({}^{***}\) indicate the significance of the test at 5\(\%\) and 10\(\%\) levels of significance.  
\end{table} 
Table 2: MK trend test (\(Z\)) statistics, Sen’s slope, and \(p\) value for the LST trends analysis. Figure 7: Spatial distribution of (**a**) Mann–Kendall, (**b**) Sen’s Slope, (**c**) Level of Significance (_p_-value), (**d**) Statistically significant data at 99\(\%\) level of confidence. The results of the spatial-temporal changes of LST over different seasons are given in Figure 8. The overall mean of the seasonal LST varies from \(-26\) to \(60\)\({}^{\circ}\)C throughout Pakistan. During the overall seasons, the highest LSTs were observed in region II, particularly in the summer season, which reached up to 50.86 \({}^{\circ}\)C, which is the highest among the other regions and seasons. This result can be attributable to the fact that the annual rainfall is below average. Furthermore, barren ground, which is more susceptible to LST changes than vegetation-covered land, could be another factor for the rise in LST. Similarly, the lowest LST were observed in region V in all seasons, especially in the winter season, where the mean LSTs of this region were decreased up to \(-9.7\)\({}^{\circ}\)C; there are some places that contain higher LSTs, especially in the southern parts of that region. During the autumn and spring seasons, similar trends were observed, followed by winter and summer, especially in regions II and V. The mean LSTs of the spring and autumn season reached up to 42 and 46 \({}^{\circ}\)C, respectively, in region II. The results of the trend analysis and Sen's slope at seasonal scales were presented in Table 3. The highest increasing trend (0.20 \({}^{\circ}\)C) at a 1% level of significance (\(p<0.01\)) was observed in region V during the summer season; there were also increasing events in other seasons, except for the spring season. Another warming event was observed in region II during the summer season. Contrary, the highest cooling trend was observed in region I during the autumn season (\(-0.08\)\({}^{\circ}\)C) which is highest among all seasons and regions. The factors attributed to this cooling trend could be the Khirthar mountainous regions, which cover an area of about 9000 square kilometers, with the highest peak of 2260 m. Due the high altitude, the LST of this region does not significantly increase in 2018 and 2021. When we investigate the low altitude/flat surfaces, the only region IV is a region where the change rate of LST significantly increases significantly in the summer seasons throughout the season, and the highest heating trend has a magnitude of 0.08 \({}^{\circ}\)C.