University of Oulu

Hekmatzadeh, A.A., Kaboli, S. & Torabi Haghighi, A. New indices for assessing changes in seasons and in timing characteristics of air temperature. Theor Appl Climatol 140, 1247–1261 (2020).

New indices for assessing changes in seasons and in timing characteristics of air temperature

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Author: Akbar Hekmatzadeh, Ali1; Kaboli, Sadegh1; Torabi Haghighi, Ali2
Organizations: 1Department of Civil and Environmental Engineering, Shiraz University of Technology, PO Box 71555-313, Shiraz, Iran
2Water, Energy and Environmental Engineering Research Unit, University of Oulu, PO Box 4300, FI-90014, Oulu, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 1.2 MB)
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Language: English
Published: Springer Nature, 2020
Publish Date: 2020-06-09


Previous studies examining climate change and changes in the timing of seasons have used a fixed temperature threshold for season onset. In this study, the timing of seasons was determined using non-fixed threshold methods. Twelve new timing indices were defined to account for shifts in seasons and season onset day, thermal centroid day, and length. The Mann-Kendall test, Theil-Sen’s slope estimator, sequential Mann-Kendall test, and least square linear regression were used to assess trends. The timing indices were examined using data from two meteorological stations in Iran with 50 years of records. Spatio-temporal variations in each index over 30 years (1987–2016) were then determined for Khuzestan province in southwestern Iran. Trend analysis for several indices indicated that the timing of seasons had probably changed in the south and west of the study area, while mountainous regions showed non-significant trends. Based on the hottest and coldest 90-day periods (summer and winter, respectively), during the three decades studied, spring lengthened by 5–10 days/decade in the plain region of Khuzestan province and autumn shortened by about 5–8 days/decade. The centroid of winter occurred earlier, by 2–5 days/decade, in the plains area, while the thermal centroid of summer did not change significantly. Overall, the difference between the thermal centroid of winter and summer (Cwin-sum) in the plains area significantly decreased, by 6–8 days/decade, in the 30-year period.

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Series: Theoretical and applied climatology
ISSN: 0177-798X
ISSN-E: 1434-4483
ISSN-L: 0177-798X
Volume: 140
Issue: 3-4
Pages: 1247 - 1261
DOI: 10.1007/s00704-020-03156-w
Type of Publication: A1 Journal article – refereed
Field of Science: 1171 Geosciences
218 Environmental engineering
Funding: Open access funding provided by University of Oulu including Oulu University Hospital. This study was supported by Maa- ja vesitekniikan tuki Foundation (Grant No. 13-8186-16).
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