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Lookup NU author(s): Dr Haider Ali, Professor Hayley Fowler
This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).
© The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2025.We explore the relationships amongst duration, total amount, mean and maximum hourly intensity of rainfall and spatial scale for more than a thousand rain gauges covering a diverse range of tropical and subtropical (30°N-30°S) climates, from arid (< = 200 mm year⁻1) to very wet (> 3000–4000 mm year⁻1). We find that the interannual variation of seasonal (3-month) amounts is primarily driven by wet hour frequency rather than the mean intensity of rainfall. A total of 3.5 million local wet spells (WS: consecutive wet hours with at least 1 mm of rain) are then systematically analyzed. WS lasting 5 h or less account for 80% of wet hours and of total rainfall. The amount of rainfall during a local WS is most strongly controlled by its duration and then its mean hourly intensity, but these WS characteristics are nearly independent. The 3.5 million local WS are then grouped into a reduced set of 7 “canonical” wet spells (cWS) from the 24 hourly rainfall from their start (dry hours < 1 mm are reset to 0), firstly square-rooted and then simply normalized by the 24 hourly means across all WS. Despite some relatively small differences amongst national networks, the seven cWS offer a general framework for tropical rainfall variability seen through the prism of the local WS. About 72% of the WS included in two categories (cWS#1, 51,8% of the WS, and #3, 20% of the WS) are short and result in negligible amounts of rainfall. Two other categories (cWS#2, 8.8% of the WS, and #4, 4.9% of the WS) are short but with very high mean intensity and have the smallest spatial scales. Additionally, two categories (cWS #6, 3.9% of the WS, and cWS #7, 0.9% of the WS) are long-lasting, moderately intense and cover the largest areas. The final category (cWS#5, 9.4% of the WS) is moderately long in duration and less intense compared to cWS#2, #4, #6 and #7. Hourly extremes tend to occur primarily during cWS#2 and cWS#4, contributing the least to the total number of wet hours, and then during cWS#6. Daily extremes tend to occur more in cWS#7 and #6, which are the longest cWS, but with a significant contribution from the short intense cWS#4. A larger contribution of cWS#2 and cWS#4 to 3-month amounts tends to decrease the spatial scale of their interannual variations.
Author(s): Moron V, Cornillault E, Ali H, Fowler HJ, Robertson AW
Publication type: Article
Publication status: Published
Journal: Climate Dynamics
Year: 2025
Volume: 63
Issue: 6
Online publication date: 05/06/2025
Acceptance date: 04/05/2025
Date deposited: 16/06/2025
ISSN (print): 0930-7575
ISSN (electronic): 1432-0894
Publisher: Springer Science and Business Media Deutschland GmbH
URL: https://doi.org/10.1007/s00382-025-07714-8
DOI: 10.1007/s00382-025-07714-8
Data Access Statement: The hourly dataset from French overseas territories in the tropical zone comes from MeteoFrance (https://donneespubliques.meteofrance.fr/). These data are free since January 1, 2024. The repository of the GSDR dataset is located at https://zenodo.org/recor ds/8369987.
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