From Dry to Temperate: How Climate Change Alters Growing Seasons?

Abstract

The thermal growing season, which represents a plant's theoretical growth season, is a key indicator of phenology's response to climate change. Using thermal growing season indices (start, end and length) and their sensitivity to air temperature, this study examines how climate change impacts them. For various climate types of Iran, Mann–Kendall and Sen's slope tests were applied to examine trends in thermal growing season indices at two temperature thresholds: 5°C (for cold-season plants) and 10°C (for tropical plants) between 1995 and 2020. Using a novel heuristic algorithm, multiple linear regressions were used to determine the most influential seasonal air temperature indices including mean, range and extreme on thermal growth indices as well. Plants in cold and temperate climates experienced significant early onset and lengthening of their growing seasons, with tropical plants on northern coasts experiencing the earliest onset (14.7 days/decade) and the lengthening growing season (16 days/decade). For plants in cold climates, the end of the growing season was also delayed (5 days/decade). The onset growth season was most sensitive to spring minimum and average temperatures in cold and temperate climates, while it was most sensitive to winter average temperatures in dry climates. In cold climates, changing spring and winter temperature ranges also affected the onset of the growing season, while in dry climates, changing autumn temperature ranges affected the end of the growing season. However, extreme temperatures only affect the end of the growing season in temperate climates. Furthermore, the early onset of the growing season is the primary factor contributing to the lengthening of the growing season in all climates. The findings of this study can assist in developing and implementing agriculture and water resource management strategies that mitigate climate change's adverse effects.