Effects of Climate Change on Moroccan Coastal Upwelling: Relationships between the NAO, Upwelling Index, and Sea Surface Temperature (1978-2024)

TL;DR

This study analyzes how climate change affects Moroccan coastal upwelling from 1978 to 2024, revealing complex interactions among climate indices, local ocean conditions, and temperature trends with implications for regional ecosystems and industries.

Contribution

It provides a comprehensive analysis of the spatio-temporal dynamics and causality between NAO, upwelling, and SST, highlighting recent acceleration in warming and upwelling decline.

Findings

Strong winter NAO--CUI coupling ($r=+0.65$)

Summer upwelling decline ($-0.0635$ units/decade)

SST warming trend (+0.149°C/decade)

Abstract

This study investigates climate change impacts on Moroccan Atlantic coastal upwelling (21$^{\circ}$--35$^{\circ}$N), analyzing interrelationships among the North Atlantic Oscillation (NAO), Coastal Upwelling Index (CUI), and Sea Surface Temperature (SST) from 1978--2024 using ERA5 reanalysis data. Methods include index calculations, seasonal correlations, Granger causality tests, linear trends, and breakpoint detection to evaluate spatio-temporal dynamics and causality. Results reveal seasonal variability: strong NAO--CUI coupling in winter (DJF; $r = +0.65$), local upwelling dominance in summer (JJA; $r = -0.46$ CUI--SST), and a north--south gradient with intense southern upwelling (mean Ekman transport $37.1 \pm 34.5$ m$^3$/s/100m). Trends show significant SST warming ($+0.0736$ units/decade; $+0.149^{\circ}$C/decade spatially), summer upwelling decline ($-0.0635$ units/decade in JJA), and weak NAO shifts. Granger causality indicates rapid local forcing (CUI $\to$ SST, lag 1--3 months), delayed teleconnections (NAO $\to$ SST, lag 2--4 months), and ocean feedback (SST $\to$ NAO, lag 7--11 months). Breakpoints (1992--1997) signal warming acceleration, highlighting a paradox of global SST rise amid localized upwelling-induced cooling per Bakun's hypothesis. Findings underscore implications for fisheries, aquaculture, and tourism, advocating adaptive management via seasonal forecasting. Keywords: Coastal upwelling, NAO, SST, climate change, Granger causality, Moroccan Atlantic, Ekman transport, spatio-temporal variability.