Introduction
Today, with the development of urbanization, cities have influenced the local, regional, and even global climate. One of the key elements in climatology studies is microclimate, since the effects of small local climates cause global climate changes. These changes have significantly contributed to the increase in the average global temperature. Vegetation loss, changes in land use, migration from rural to urban areas (population growth), agriculture, deforestation, and most importantly, the increase in greenhouse gases and the heat dissipated by human activities have caused urban warming and intensified the heat island effect in cities. This study aims to investigate the spatiotemporal changes in regional temperature and the extent of the urban heat island (UHI) in Tehran Province, Iran. 

Methods
To investigate the temperature, the Mann-Kendall statistical test and Landsat 8 satellite and MODIS images were used. In the first step, the daily temperature of Tehran synoptic stations (Shamiran, Chitgar, Mehrabad, Abali, Firouzkoh, and Geophysics) from 1996 to 2020 were obtained from the National Meteorological Organization. Then, to investigate the trend of temperature change based on a monthly time series over time, the Mann-Kendall test was used. To measure the average regional temperature based on the MODIS images (MOD11C3 product), 53 monthly time series images of land surface temperature  (LST_Day_CMG) were downloaded from the NASA’s website for the years 2014-2024. Then, in order to prepare the map and profile of the UHI, Landsat 8 satellite images (band 10) were obtained for a period of one year (2024). After determining the maximum land surface temperature (LST) in Tehran, the temperature profiles of four districts (no. 1, 18, 9, 22) from among 22 different districts were drawn. Finally, using the Climate Engine software, the normalized difference vegetation index (NDVI) and LST changes were investigated.

Results 
Temperature time series analysis of selected stations (Shimiran, Chitgar, Mehrabad, Abali, Firouzkoh, and Geophysics) for 1996-2020 showed an increasing trend in all stations except for Chitgar station. Examining the average regional temperature of cities in Tehran Province for the years 2014-2024 based on the MODIS data showed the highest regional temperature in July and August. In these months of 2015, Varamin and Rey cities experienced the highest LST (52.50 °C). Three years later in these months of 2018, this figure reached 52.97 °C. In 2022 and 2023, in the same months, Varamin, Mallard, Rey, Pakdasht, and Pishva cities experienced a temperature of 48 °C. 
Expansion of construction, vegetation loss, and consumption of fossil fuels were the factors involved in increasing the LST. Investigating the relationship between the trend in NDVI and LST based on Landsat 8 images between 2013 and 2024 showed that they had a direct and inverse relationship with each other, such that in June, July, and August of 2017, 2019, and 2024, it was observed that with a slight increase in NDVI, the LST reached 51.21 °C. This was more evident in the western, northern, and southwestern regions. Moreover, on October 28, 2020, the NDVI was -0.0, while in December and November of 2018, 2023, and 2021, it reached -0.03, -0.03, and -0.04, respectively. Thus, the slight increase in vegetation cover has not been able to justify the increase in temperature in the summer and autumn seasons. Investigating the expansion of UHI based on Landsat 8 images in 2024 showed that the most heat sources were in the south, southeast, west, north, southwest, and northern areas of Tehran, but the LST in June 2024 reached 52 °C, which was more evident in districts 9 and 22. Although air temperature and LST showed different values in the districts of Tehran, they had similar patterns of changes in June and July. 

Conclusion
This study reveals that climate change, caused by global warming, summer subtropical high-pressure system, and air subsidence in Iran, as well as increased greenhouse gas emissions, land-use changes, and vegetation loss, have significantly altered the spatiotemporal patterns of temperature in urban areas of Tehran. The findings of this research can be utilized in developing long-term plans for adapting to climate change in the field of urban crisis management.

Ethical Considerations
Compliance with ethical guidelines
All ethical principles were considered. Since there was no experiment on human or animal samples, the need for an ethical code was waived.

Funding
This work is based upon research funded by Iran National Science Foundation (INSF) under project (Grant No.:4038495).

Authors' contributions
Conceptualization, software/statistical analysis, and initial draft preparation: Niloofar Mohammadi; Supervision, review and editing: Zahra Hejazizadeh, Parviz Zeaiean Firouzabadi, and Alireza Karbalaee.

Conflicts of interest
The authors declared no conflict of interest.

Acknowledgments
The authors would like to thank the Iran National Science Foundation (INSF) for the financial support.



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