Zeroualı et al. (2025) Linking the North Atlantic Oscillation to rainfall variability and dynamics in Algeria through GIS and wavelet theory

Identification

• Journal: Scientific Reports
• Year: 2025
• Date: 2025-11-28
• Authors: Bilel Zeroualı, Mohamed Chettih, Faten Nahas, Paolo Porto, Nadjem Bailek, Abid Ouadja, Jihad Younis, El‐Sayed M. El‐kenawy, Shabana Urooj, Youssef M. Youssef
• DOI: 10.1038/s41598-025-29840-3

Research Groups

• Laboratory of Architecture, Cities and Environment, Faculty of Civil Engineering and Architecture, Department of Hydraulic, Hassiba Benbouali University of Chlef, Algeria.
• Vegetal Chemistry-Water-Energy Research Laboratory, Faculty of Civil Engineering and Architecture, Department of Hydraulic, Hassiba Benbouali University of Chlef, Algeria.
• Research Laboratory of Water Resources, Soil and Environment, Department of Civil Engineering, Faculty of Civil Engineering and Architecture, Amar Telidji University, Algeria.
• Department of Geography, College of Humanities and Social Sciences, King Saud University, Saudi Arabia.
• Department of Civil and Environmental Engineering, Federal University of Paraíba, Brazil.
• Stokes School of Marine and Environmental Sciences, University of South Alabama, USA.
• Dipartimento di Agraria, University Mediterranea of Reggio Calabria, Italy.
• Faculty of Geographical Sciences, Kazimierz Wielki University, Poland.
• Laboratory of Mathematics Modeling and Applications, Department of Mathematics and Computer Science, Faculty of Sciences and Technology, Ahmed Draia University of Adrar, Algeria.
• Department of Mathematics, Aden University, Yemen.
• School of ICT, Faculty of Engineering, Design and Information & Communications Technology (EDICT), Bahrain Polytechnic, Bahrain.
• Applied Science Research Center, Applied Science Private University, Jordan.
• Department of Electrical Engineering, College of Engineering, Princess Nourah bint Abdulrahman University, Saudi Arabia.
• Geological and Geophysical Engineering Department, Faculty of Petroleum and Mining Engineering, Suez University, Egypt.

Short Summary

This study regionally analyzes the relationship between the North Atlantic Oscillation (NAO) and rainfall in northeastern Algeria using wavelet theory and GIS, revealing a strong and consistent NAO influence in the north that diminishes southward, offering potential for improved rainfall forecasting.

Objective

• To assess the time scales at which the North Atlantic Oscillation (NAO) influences rainfall in northeastern Algeria.
• To identify coherent spatiotemporal patterns between the NAO and regional rainfall variability using advanced multiscale wavelet techniques and hierarchical clustering.

Study Configuration

• Spatial Scale: Northeastern Algeria, covering approximately 110,000 square kilometers, specifically 69 monthly rainfall stations across nine hydrological sub-basins.
• Temporal Scale: Monthly data for the period 1970–2007 (37 years).

Methodology and Data

• Models used: Cross-Wavelet Transform (XWT), Wavelet Coherence Transform (WCT) with Morlet mother wavelet, Hierarchical Ascending Classification (HAC) using Ward’s linkage method and Euclidean distance, Geographic Information System (GIS). Statistical significance was tested against an AR(1) (first-order autoregressive) red-noise background.
• Data sources: Monthly rainfall time series from 69 stations obtained from the Algerian National Agency for Water Resources (ANRH). North Atlantic Oscillation (NAO) index.

Main Results

• Hierarchical Ascending Classification (HAC) identified three homogeneous clusters of NAO-rainfall relationships:
  • Cluster 1 (Northern region): Strong and persistent coherence, particularly in the 4–16 month (seasonal to annual) and 16–32 month (interannual) bands. These modes contribute over 40% each to total variance.
  • Cluster 2 (Central transitional region): Moderate and less stable coherence, with discernible annual (8–16 months) and interannual (1–3 years) modes contributing over 80% combined, and decadal modes (64–128 months) contributing approximately 25%.
  • Cluster 3 (Southern arid region): Weak and intermittent associations, with short- and medium-term modes showing reduced influence, and long-term decadal modes (>64 months) playing a dominant role, contributing approximately 40% to total variance.
• Wavelet Coherence Transform (WCT) proved more reliable than Cross-Wavelet Transform (XWT) by suppressing spurious correlations and providing clearer insights into localized covariability.
• Phase function analysis showed strong phase alignment in northern regions during early months, indicating significant NAO influence, while central and southern regions displayed more variable phase functions.
• The NAO's influence on rainfall exhibits a clear spatial gradient, decreasing from north to south across Algeria.

Contributions

• First regional-scale study in Algeria to employ multiscale wavelet techniques (XWT and WCT) combined with Hierarchical Ascending Classification (HAC) and GIS to assess the dynamic and time-frequency relationships between NAO and regional precipitation.
• Demonstrated the superior reliability of WCT over XWT for teleconnection analyses by providing a clearer depiction of localized covariability and suppressing spurious correlations.
• Provided a new regionalization of rainfall patterns based on NAO-rainfall relationships, delineating three distinct climatic zones with varying NAO influence.
• Emphasized the potential of NAO as a predictive indicator for seasonal and interannual rainfall variability, particularly for improving artificial intelligence-based rainfall forecasting and drought early warning systems in Algeria.

Funding

Not applicable.

Citation

@article{Zeroualı2025Linking,
  author = {Zeroualı, Bilel and Chettih, Mohamed and Nahas, Faten and Santos, Celso Augusto Guimarães and Porto, Paolo and Bailek, Nadjem and Ouadja, Abid and Younis, Jihad and El‐kenawy, El‐Sayed M. and Urooj, Shabana and Youssef, Youssef M.},
  title = {Linking the North Atlantic Oscillation to rainfall variability and dynamics in Algeria through GIS and wavelet theory},
  journal = {Scientific Reports},
  year = {2025},
  doi = {10.1038/s41598-025-29840-3},
  url = {https://doi.org/10.1038/s41598-025-29840-3}
}