Evaluation of Long-Term Temperature and Precipitation Changes in 22 Cities of Iran over Six Decades (1958–2017)

Background and Objectives: Climate change, as one of the major environmental challenges of the 21st century, has significantly altered global temperature and precipitation patterns, particularly in arid and semi-arid regions. Due to Iran’s unique geographical location and diverse climatic conditions, it has experienced noticeable and concerning changes in its climate parameters over the recent decades. The main objective of this study is to conduct a comprehensive assessment of long-term trends in annual and seasonal temperature and precipitation in 22 selected cities across Iran over a 60-year period (1958–2017), and to analyse the underlying climatic patterns using robust statistical approaches.
Materials and Methods: In this study, annual mean temperature and precipitation data were collected from meteorological stations in 22 selected cities across the country. The cities were selected to ensure maximum representation of Iran’s climatic diversity, ranging from the arid central regions to the humid northern and semi-arid western and southern areas. This geographical diversity allows for a more comprehensive analysis of climate variability across the nation. To detect climate trends, non-parametric statistical methods were employed, including the Mann–Kendall test to evaluate trend significance and the Sen’s slope estimator to quantify the rate of change. Furthermore, the study period was divided into two 30-year intervals (1958–1987 and 1988–2017) to enable a more precise comparison of long-term climate changes over time.
Results: The results indicated that most cities experienced a statistically significant increase in annual temperature. In some areas, such as Mashhad, Tehran, and Sanandaj, the increase exceeded 1.5 °C. Conversely, cities like Bandar Abbas, Zanjan, and Shahrekord showed a relative cooling trend. The most notable temperature increases were observed during spring and summer. Regarding precipitation, over half of the studied cities experienced substantial declines in annual rainfall, including Tabriz (more than 22% decrease) and Kermanshah (over 50 mm reduction). However, cities such as Isfahan and Shiraz exhibited slight increases in precipitation. Seasonal analysis revealed that winter precipitation showed a declining trend in most regions, which may have serious environmental and social implications.
Conclusion: The prevailing climatic trend in Iran over the past six decades is characterized by significant warming accompanied by declining precipitation in many regions. These changes can have numerous negative impacts, such as increased drought frequency, reduced water availability, agricultural stress, and a rise in natural hazards. The findings highlight the urgent need for targeted planning and implementation of adaptive strategies, including integrated water resources management, adoption of climate-resilient agricultural practices, and strengthening the resilience of vulnerable areas. It is also recommended that future studies focus on long-term predictive modeling and regional analyses to gain deeper insights into the evolving climate dynamics of the country.