Assessment of spatiotemporal changes of the length and starting date seasons in the west of Iran

There is evidence that human activities are affecting global dynamics. The consequences of changes in the duration of the annual seasons and daily temperatures will imply drastic impacts on human and natural ecosystems. However, estimations related to the duration of the seasons considering the daily temperatures are scarce and could help to foresee negative effects with irreparable consequences. This study investigates the spatiotemporal variation of length and start date of each annual season based on temperature criteria by analyzing daily data of synoptic stations in western Iran from the period 1977-2015. Our results demonstrated that the starting date of summer shows a tendency advanced and the starting date of winter has been delayed. Moreover, spring is coming earlier. On the other hand, winter ends earlier and fall is delayed, with longer summers and shorter winters as a result. The starting date of summer differs from 0 to 2 d advanced in the southwest of the study area and 4-6 d advanced in the central and southeast parts. The starting date of winter on average has been delayed by 2 days and the length of the season has been shortened by 5 days. The changes for spring and fall are relatively smaller. Particularly, spring started earlier by 4.2 days but was extended by 1.8 days, and the fall season has started delayed by 0.8 days but extended by 0.4 days. This study provides simple information to stakeholders and policymakers so that they should focus on the issue and start developing efficient plans to reduce the negative impacts on the temperatures, shorter winters and the earlier spring, which could affect the floriation and animal behaviors among others.

Automated summary

This study investigates the spatiotemporal variation of length and start date of each annual season based on temperature criteria by analyzing daily data of synoptic stations in western Iran from 1977 to 2015. The results show that the starting date of summer has advanced, the starting date of winter has been delayed, and spring is coming earlier. Winter ends earlier and fall is delayed, resulting in longer summers and shorter winters. This study provides important information for stakeholders and policymakers to develop efficient plans to reduce the negative impacts of changing temperatures and seasonal timing.