Vol.:(0123456789) 1 3 Theoretical and Applied Climatology https://doi.org/10.1007/s00704-022-04259-2 ORIGINAL PAPER Evaluating the onset, end, and length of seasons in selected stations in Iran Reza Doostan 1  · Bohloul Alijani 2 Received: 9 March 2022 / Accepted: 21 October 2022 © The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature 2022 Abstract Specifying seasons is one of the most signifcant and arduous parts of climatology studies. In the present study, seasons are defned to apparent temperature index. For determining changes in the length, start, and end dates of the season in Iran in line with global climate change, in this research we used daily data of apparent temperature for 32 synoptic stations with locations and topography over a 60-year period (1959–2018). Temperature indices used for determining the start of seasons are thresholds of apparent temperatures of 0 and 20 degrees, with a 10-day continuation and without reverting to the initial conditions during this period for winter and summer, respectively. In the same vein, transitional seasons were specifed and changes were analyzed using linear regression. The fndings revealed that, in various regions, the start of spring and summer occur earlier while the start of fall and winter are delayed. The biggest statistically signifcant changes are observed at the start of the spring and fall seasons, as the increase is 2.25 days for summer and 1.5 days for winter per decade. Therefore, the duration of cold seasons have decreased and the duration of warm seasons have increased in climatic regions. These changes are statistically signifcant in foothill and high-altitude regions; the hot and dry climatic range is expanding with the increase and decrease of the summer and winter length, respectively. However, considering the inhomogeneity of altitude and geographical phenomena in the Iranian plateau and its fat northern and southern regions, these changes are not uniform or equivalent. We can say that, overall, climate change, as a direct factor infuencing season change and climatic belts, plays a more infuential role in comparison with local factors. 1 Introduction According to the reports of the Intergovernmental Panel on Climate Change, in the second half of the previous century, the global warming has been accompanied by an increase in the levels of CO 2 production caused by humans’ con- sumption of fossil fuels, and this trend is expected to con- tinue in the future. The most recent report of the Intergov- ernmental Panel on Climate Change denotes an increase of 0.99 (1.4–1.8) degree in earth’s temperature compared to the period of 1850–1900 which, in an optimistic scenario by midcentury, will result in an increase of 1.5 to 2 degrees compared with the base period (Allan et al. 2021). The consequences of climate change include increased environmental hazards and climatic abnormalities which entail more occurrence of droughts on the globe (Dai 2011), east Africa (Haile et al. 2020), and northeast Spain (Gaitan et al. 2020); torrential rains and foods on the globe (Markus 2019; Tabari 2020); and heat waves on the globe (Marx et al. 2021), Germany (Zacharias et al. 2015), Africa (Engdaw et al. 2021), and north China (Kang et al. 2018). Some of the consequences of climate change that afect the earth’s ecosystem are extinction in some parts of the world (Thomas et al. 2004), decrease in the population of plants and animals, and immigration in diferent parts of the world (Aitken et al. 2008; Carey 2009; Gomez-Ruiz and Lacher, 2019). The behavior of plants and animals is in line with the movement of the sun, changes in environmental tem- perature, and the start and end dates of thermal seasons. Therefore, global warming and man-made climate changes cause changes in the characteristics of seasons. Researchers have studied these changes using varied methods such as fxed thermal thresholds (Jaagus et al. 2003; Majewski et al. 2014; Kitowski et al. 2019; Ruosteenoja et al. 2020), classifcation of air masses (Lamb, 1950; Cheng et al. * Reza Doostan doostan@um.ac.ir 1 Department of Geography, Ferdowsi University of Mashhad, Mashhad, Iran 2 Department of Geography, Kharzmi University, Tehran, Iran