# Spatiotemporal Variation of Land Surface Temperature Retrieved from FY-3D MERSI-II Data in Pakistan
## 5 Discussion  
The TFSW algorithm's accuracy and adaptability were evaluated by comparing the LSTs of MERSI-II with MYD11A1 and MYD21A1 LST over various study regions. The LST difference ranged between 1.74 and 5.2 \({}^{\circ}\)C over the different regions of Pakistan. The MERSI-II LST performs well with the MODIS MYD11A1 LST product; the error range was between 1.94 and 4.27 \({}^{\circ}\)C, which is slightly higher but close to the several published studies [7; 12; 43; 44]. The regions that experience the highest LST difference could possibly be due to the surface types, and the presence of humidity produces larger uncertainties [44]. Regarding the LST distribution, the highest LSTs were observed in the southern areas, and the lowest in the northern areas. The amount of solar radiation energy received by  
Figure 12: (a,b) Interannual Mean LST, including its frequency histogram for the years of 2005 to 2018 throughout the Pakistan.  
the ground decreases as latitude increases. As a result, the annual mean LST distribution pattern is characterized by high values in the southern regions and low values in the northern parts. There are, however, some locations that do not follow this trend. Because the areas where the Indus River flows, particularly in the country's central lower latitudes, are largely productive, resulting in moderate heat preservation on the ground, it has a lower annual mean LST than its nearby places. The great mountainous region occurred in northern areas, which is Pakistan's greatest altitude region, with an average elevation of above 5000 m. Because the location is at a high elevation, the air near the surface is thin, resulting in poor heat retention on the ground and a lower annual mean LST than in other parts of the country. According to the MK trend analysis, the highest warming impacts (0.019 \({}^{\circ}\)C/Year) were noted in the northern areas, with a high level of significance. This scenario was also observed in seasonal trends as well as long-term analysis trends. The reasons for this increasing are possibly the impacts of global warming and climate change [45]. By taking into account meteorological data from two sites, [PERSON] et al. [46] looked into changes in temperature in the Upper Indus Basin. In line with this investigation, they observed that the mean temperature increased by 0.63 \({}^{\circ}\)C in Skardu, whereas it recently declined by 0.137 \({}^{\circ}\)C in Gilgit. The source of the decreasing trends in southern region I is unknown. There are strong increasing trends through seasonal and monthly analyses in regions I and II. The lack of rain and growing drought have had a substantial impact on the temperature fluctuations of Southern Pakistan. The hottest temperatures have had a significant detrimental influence on Pakistan's primary crops, such as wheat and cotton. Early in the spring season, a minor heat wave (13 days over the usual 2-3 \({}^{\circ}\)C temperatures) resulted in a 28 percent decline in wheat grain yield.  
When evaluating the results, it is important to take into account the limitations of the current study. The remote sensing data are not enough to obtain precise LST trends. However, the various factors that affect LSTs are still not considered in this study, such as elevation, land cover types, and water vapor; even the NDVI has a considerable influence on LSTs [47]. To ensure the reliability of the results, future studies should employ LST data, including elevation, land cover types, water vapor, etc.