# Spatiotemporal Variation of Land Surface Temperature Retrieved from FY-3D MERSI-II Data in Pakistan
## 4 Results
### Spatial Distribution of the Annual Mean LST  
The spatial distribution of the annual mean LSTs of Pakistan is almost the same in 2018 and 2021; small variations were observed, as the time span (i.e., 4 years) is not very long. The annual mean LST of Pakistan ranged between \(-15\) and \(55\)\({}^{\circ}\)C (Figure 6). A bar chart was developed to demonstrate the linear change of the annual mean LST between 2018 and 2021 over the sub-regions of the study area, and differential variations in pixel scale between two raster datasets were performed to validate substantial upward or downward variations. It was observed from the annual mean LST that 2018 was the coldest year (33.63 \({}^{\circ}\)C), while 2021 was the warmest (34.42 \({}^{\circ}\)C). The temperature difference between the coldest and warmest years was about 0.79 \({}^{\circ}\)C.  
When the geographical characteristics of the location are considered, it was discovered that the low elevation increased thermal insulation, resulting in a greater LST. In terms of geographical cover, Pakistan's greatest desert, Thar, is located around the Indian border in the southeast. The desert covers an area of 175,000 square kilometers, including significant regions of Pakistan and India. It is Pakistan's largest desert, and Asia's only subtropical desert that absorbs sun radiation. During the analysis of the spatial distribution of annual mean LST throughout the sub-regions, the region II exhibits the highest annual mean LST, varying between 41 and 42 \({}^{\circ}\)C. The same scenario was observed in region I. Due to various geographical surface features, region III is slightly different, with a mean LST of 36 \({}^{\circ}\)C. Region IV is the transitional zone between the temperate and severe climate zones; the annual mean LST of this region is around 31 \({}^{\circ}\)C, but it varies greatly across the landscape. The lowest LST values were discovered in region V, which were decreased by up to \(-22\)\({}^{\circ}\)C; however, in the southern parts of this region, the temperature was increased up to 39 \({}^{\circ}\)C.  
Figure 5: Spatial distribution of (**a**) MYD11A1, (**b**) MYD21A1, and (**c**) MERSI-II LST data. The dotted line represents the profile extraction location. (**d**) Latitudinal profile of three different LST data.  
We calculated the linear mean LST difference by subtracting the data values from two raster datasets. The warming and cooling of the LST trend were shown by positive and negative values. Figure 6e depicts the results after subtracting the initial and final raster data values at the pixel scale, while Figure 6f depicts the mean annual difference. Northern Pakistan is cooled more than Southern Pakistan, resulting in the highest cooling effect in the north and a moderate cooling effect in the south. However, many locations of region IV have an LST difference of less than 0 \({}^{\circ}\)C, which is primarily cooling. The largest warming trend (0.68 \({}^{\circ}\)C) was identified in region I, whereas the minimum warming trend (0.32 \({}^{\circ}\)C) was recorded in region IV. The explanation for the cooling trend in region V is unknown, possibly due to the missing data of thin clouds. The warming tendencies in regions I and II, on the other hand, are due to changes in their geographical land cover types.