In mid-March, still winter, the Iberian Peninsula witnessed a remarkable haze event of unprecedented size, intensity, and duration. Saharan dust overflowed across the peninsula and even reached Great Britain. Air quality deteriorated noticeably as the visit of the dust began on the 14th and lingered until the 22nd. The skies turned orange and became turbulent with a sharp drop in visibility, driven by a large extratropical cyclone named Storm Celia. The snowy surfaces below were coated with a dusty, earthy layer. From the 23rd to the 28th, the continuities persisted with fresh mud rain especially noticeable from the south. In Málaga, authorities advised staying indoors due to the elevated risk of slips on muddy streets and pavements.
The dust originated from the world’s largest desert region, the hot subtropical Sahara. Its climate features strong subtropical subsidence and a pronounced continental influence, with the cold Canary current having a limited, though not insignificant, effect. The Sahara spans about 10,000,000 square kilometers and runs roughly 5,000 kilometers from the Atlantic to the Red Sea. It stretches about 2,000 kilometers in latitude and width, from the southern Atlas to the Mediterranean, extending to an imaginary line that marks the Sahel’s start near San Luis up to Khartoum. Precipitation in this zone is exceedingly scarce and highly irregular, and potential evapotranspiration ranges from about 2,000 to 6,000 millimeters. The region is hyper-arid, with years sometimes passing without rain, and occasionally receiving a few millimeters in alternating years at several observatories, a pattern that intensifies further in the Eastern Sahara. Large daily temperature swings, sometimes around 50 degrees Celsius, accompany minimal water vapor, clear skies, intense daytime insolation on highly reflective surfaces, and significant nocturnal heat loss. Heat can persist for hours in the shade, with temperatures climbing well above 50°C, while dawn may bring subfreezing readings.
Beyond these dust sources, historical records show how European powers interacted with the Sahara. Although England and Italy also held colonial footprints between 1883 and 1976, France dominated much of the Sahara towards the end of the 19th century, famously taking Timbuktu in 1894. The Sahara’s greatest scholars include Birot and Capot-Rey, with perhaps the most notable French expert being the Sahara specialist who authored the influential Le Sahara française in 1953, alongside researchers like Dresch, Dubief, and Ozenda. The Institut de Recherches Sahariennes and the University of Algeria contributed to this enduring body of work. The Sahara is defined by endless plateaus, the “hamadas,” wind-carved sand seas known as ergs, and deserts with skeletal soils and leached dune fields formed from sands, silts, clays, and fine fragments. The sands are transported by winds that mobilize the fine particles and can reduce even dry fog. These processes feed red or blood rain and, less often, ocher snow. The appearance of red rain is sometimes viewed as a historical omen tied to ancient disasters.
On the Iberian Peninsula, the Canary Islands and southern portions of Spain are the zones most frequently affected by dust incursions. Proximity to the Sahara and geographic position increase the likelihood of haze, particularly in the Canary Islands, where hazy conditions can occur year-round but tend to intensify in summer and autumn. All Saharan air intrusions, whether in winter or summer, are categorized as southern air only in a sense, since the dust-laden flows reach the islands from the east, southeast, and only rarely from the northeast. The term southern time captures the resonance between these flows and the dominant trade-wind regime. The difference lies not only in direction but in origin: continental Saharan air versus sea-based trade winds. Isobaric patterns—ranging from depressions to anticyclones—tend to steer easterly winds toward the archipelago. When Saharan dust arrives during summer with very hot temperatures (around 40°C) and low relative humidity (below 10%), crops and vegetation can burn, and visibility can plummet; historical extremes include 48°C in Arrecife, Lanzarote, in July 1942. The duration of Kalima over the Canary Islands ranges from roughly 3 to 15 days, with a documented maximum stretch of 25 days. The central regions of the islands, with greater orographic relief relative to the cold current, experience a denser air cushion as the Saharan air mass descends. The dense haze over the Canaries can visibly affect air quality and even mouthfeel, often making the sky very cloudy and sometimes reducing visibility to less than 1 kilometer, which can ground air travel. Locust outbreaks also accompanied Saharan dust events in some historical periods, adding another layer of concern.
Several atmospheric conditions trigger haze in the Iberian Southeast. High pressure systems, a large Atlantic extratropical cyclone, and the trough associated with Storm Celia coincide with a late-season dust intrusion that delivered mud rain and, on occasion, mustard-colored snow. The most characteristic haze drivers in the Iberian Southeast are the so-called Algerian lows. These cyclogenetic developments arise from Saharan advection at the surface, dust suspended in the air, and cold air troughs aloft, which intensify vertical gradients and establish a low-altitude jet stream. This instability favors dust-laden disturbances. Some frontal-type storms entering the Mediterranean via Gibraltar descend latitude enough to affect dune fields, lifting desert dust into cyclonic motion. In other cases, a pressure difference or gradient modulates Saharan flows from the second or third quadrants, steering dust across regions.
Recent observations over the past five years indicate a possible rise in haze and mud rain episodes in temperate zones. If this trend holds across larger data sets, it might support hypotheses about subtropical shift and Hadley cell expansion, underscoring the broader importance of these atmospheric changes without overstating their immediacy.