The Iberian Southeast experiences an extremely irregular precipitation pattern, alternating extreme droughts with sudden, sometimes devastating floods. At times the weather seems to unleash rain not in buckets, but in torrents that overwhelm the land and sky alike. The impact of torrential rainfall depends heavily on how the rain concentrates over time. The flood event of 19 October 1973 near Zurgena, Almeria, stands as a stark example: 600 mm fell in just three hours, with 420 mm pouring between 1 and 2 am in a dramatic cascade. The rainfall coincided with a basin of 139 square kilometers, a total lightning surge of 1,974 m3/sec on the Rambla de Nogalte, and a severe inundation in the Murcian town of Puerto. Even larger floods have been recorded, including a surge of 2,489 m3/s on a major boulevard on 28 September 2012, exceeding all long-term return estimates by several centuries. The Riada de Santa Teresa (14–15 October 1879) remains the most infamous flood in the Segura basin and received wide attention in Spanish hydrology, described by Maurice Pardé as one of the deadliest floods in European records. A report by two civil engineers notes that at a farmhouse near the Vélez River, a major tributary of the Guadalentín, more than 600 mm could be measured in a single hour, a figure that dwarfs Alicante’s annual average of 355 mm. At one point along the Guadalentín, hourly rainfall surpassed 10 mm/min for an extended period, a rate ten times higher than typical thresholds, making the challenge nearly insurmountable. Later, in November 1987, Orihuela experienced a colossal downpour (316 mm) that altered the landscape, while a similar deluge affected Santa María in September 2019.
The calendar of devastating rains in the southeast Iberia shows a strong concentration from late summer through autumn, peaking in October. This period carries the greatest risk, even as floods may advance beyond the typical seasonal window. The early days of September often stretch into December, while autumn’s hydrological pulse is driven by the Mediterranean’s high heat capacity, inertia, and hygrometric influence on air masses that meet cooler air aloft. These factors create an environment primed for extreme rainfall events. Surface water temperature maps are a crucial reference for signaling potential risk, as the Mediterranean serves as a vast reservoir of heat and moisture that feeds these storms. While winter rains are not scarce, truly massive floods are uncommon in that season. A secondary peak can appear in spring, though it remains less intense than autumn, and summer instability tends to be sporadic rather than sustained, occasionally yielding heavy showers when cold air aloft intrudes. The downpour requires a specific atmospheric setup to organize at the surface and aloft; without it, rain remains ordinary. Moist air near saturation is a key precursor, yet this alone does not guarantee a deluge. The large-scale presence of cold air in the upper troposphere, forming a cold pocket, can evolve into a low or isolated depression (DANA) at high levels, though such a phase is not strictly necessary for massive floods. The intrusion of Mediterranean air, driven by winds from the first and second quadrants, often accompanies instability and potential ejection into deeper systems, while vertical dynamism is amplified by sharp thermal gradients and sometimes a cyclone’s return flow. Relief features, retrograde troughs, and other high-altitude lows can all contribute to triggering rainfall that becomes extreme. In short, a flood emerges when surface and upper-air conditions align, and it may require a combination of factors to produce a lasting, catastrophic event.
Alicante’s most frequent torrential downpours and true floods occur mainly in the Marquesat or Marina Alta, a region outside the Iberian Southeast’s core climate zone. Local topography favors the adoption of westerly winds arriving from the east and the Mediterranean, especially when eastern storms driven by the gregal prevail. The heart of Bajo Segura, Vega Baja, hosts a broad alluvial plain with little slope, fragile drainage, and slow drainage that encourages stagnation and flooding. Surface water can pool, overflow, and create dangerous accumulations in these low-lying zones.
On rare occasions, Atlantic storms triggered by Mediterranean air bring floods to the southeast, with eastern fronts bearing the brunt, especially when a negative phase of the North Atlantic Oscillation (NAO) aligns with destabilized air. Notable episodes include Ribera del Júcar, which saw 300–400 mm in under 24 hours on 5 November 2020, and Alto Palancia with similar totals on 22 March 2021, affecting Valencia and its metropolitan area. These events illustrate how extratropical cyclones, combined with unstable Mediterranean air rich in moisture and driven by northeastern winds, can unleash extreme downpours that defy typical seasonal expectations.
It is important to note that the drivers of heavy rain vary with surface and altitude. Surface analyses reveal multiple isobaric patterns, with a tendency toward low-pressure systems and Spain’s eastern front occupying a position on the edge of a larger anticyclonic rim. A blocking anticyclone sits to the south, shaping the eastward and southeastward flow. At higher levels, the mechanisms that lift air toward the tropopause are diverse and not limited to cold-drip processes alone. Forced convection from unstable flows, retrograde and meridional troughs, detached high-altitude lows (DANAs), cyclogenetic developments, mid-scale convective systems, and thermal instabilities that intensify hygrometry all contribute to possible floods. Localized extreme events, such as the 3 November 1987 flood at La Safor with 817 mm at Oliva, show how surface conditions and upper-air dynamics work together. Understanding a flood thus requires evaluating both surface and upper-air factors in concert.