Heavy rainfall hits southeastern Spain — similar situation last year caused devastating floods

Southeastern Spain is currently experiencing intense precipitation associated with Storm Alice, prompting the Spanish meteorological service AEMET to issue a high-level warning. As the storm remains quasi-stationary over the region, slow-moving convective rainfall with embedded thunderstorms is expected, with accumulated totals reaching 250–300 mm. Such amounts significantly increase the risk of flooding, flash floods, and landslides, particularly in coastal and mountainous areas. Due to the adverse weather, flights have been cancelled, and some areas have been evacuated. Residents have been urged to exercise caution. In this article, we analyse the meteorological causes behind this heavy rainfall and compare the situation to the devastating flood event 2024.

The meteorological phenomenon responsible for the heavy rainfall in Spain is known as a cut-off low (Fig. 2; see map). It represents a closed upper-level low-pressure system, typically identified on 500 hPa geopotential height (absolute topography) charts, corresponding to an altitude of approximately 5 km. Therefore, it can also be referred to as an upper-level cyclone.

This phenomenon forms when the southern portion (in the Southern Hemisphere, the northern portion) of a deep meridionally oriented trough of low pressure becomes detached from the main flow. Such separation frequently occurs as a ridge of high pressure amplifies and effectively blocks the prevailing westerly flow, leading to the isolation of the trough and the formation of a closed upper-level low. Once detached, the cut-off low can move independently of the surrounding large-scale circulation. In the temperature field, a cut-off low is characterised by a cold air mass aloft. The presence of this colder air enhances atmospheric instability, as the contrast between the cold upper-level air and the relatively warm surface increases vertical motions, thereby promoting the development of deep convection, heavy rainfall, and thunderstorms.

Across Europe, cut-off lows most frequently develop over the northwestern Mediterranean and northern Italy. These systems may persist for several days, producing prolonged or locally intense precipitation and flooding, particularly when they move slowly or become temporarily trapped by surrounding blocking anticyclones. Owing to their isolated nature, such systems are difficult to predict and require careful monitoring with numerical weather prediction models.

In the Northern Hemisphere, cut-off lows rotate counterclockwise, like other cyclonic systems. On satellite imagery, the presence of such a pressure system can be inferred from the rotating cloud patterns. The spiralling cloud mass over Spain, the western Mediterranean, and parts of North Africa is shown in Fig. 3. In this Cloud Phase RGB product, deep convective clouds often appear light blue to turquoise, indicating strong vertical development.

Warm waters of the Mediterranean Sea play a key role in cloud and precipitation development. During late summer and autumn, the sea often remains relatively warm, providing a significant source of moisture and energy for the atmosphere. When cold upper-level air, for example, associated with a cut-off low, moves over the region, a strong vertical temperature gradient develops, promoting the formation of convective storms. The warm sea enhances evaporation, and the latent heat released during condensation in convective clouds further strengthens upward motion. Fig. 4 shows that, during these days, the western Mediterranean is approximately 1–2 °C above the long-term average.

A meteorologically similar, but considerably more severe, situation occurred in October–November 2024, when southeastern Spain—particularly the provinces of Valencia, Albacete, and Málaga—was affected by catastrophic flooding caused by a cut-off low. The 2024 event was exacerbated by a combination of environmental factors. A key factor was the record-high sea surface temperatures (SSTs) following the summer of 2024, largely attributed to anthropogenic climate change, which substantially enhanced evaporation and provided an abundant source of moisture for convective cloud development. Another significant factor contributing to the extreme precipitation was the orography of the inland mountains in the Valencia region: moisture-laden air advected from the Mediterranean was forced to ascend along the slopes, where cooling and condensation led to the formation of rain-bearing clouds. In other words, a windward (orographic) lifting effect amplified the precipitation.

Fig. 5 shows (see map) a cut-off low over Spain at the end of October 2024. South of the Iberian Peninsula, a cut-off low is visible, which had separated from a parent trough and the polar jet stream located north of the British Isles. The detachment occurred as a ridge of high pressure built northward from the Atlantic toward the British Isles, creating a blocking pattern. This synoptic setup is similar to the current situation shown in Fig. 2. However, it is important to note that the upper-level low in 2024 was more intense than the present event. The stronger cut-off low contained colder Arctic-origin air aloft, leading to more vigorous convection and heavier precipitation.

In conclusion, this year’s intense rainfall in southeastern Spain highlights the potential for recurrent high-impact weather events, even after the 2024 floods. Storm Alice has produced heavy, slow-moving precipitation with totals exceeding 200 mm, significantly increasing the risk of flooding, flash floods, and landslides, particularly in coastal and mountainous areas. The primary meteorological driver is a cut-off low, which maintains cold air aloft over the region and enhances atmospheric instability. Additionally, the warm waters of the Mediterranean Sea supply moisture and latent heat, further amplifying precipitation. Orographic lifting by local mountains enhances rainfall even more. This year’s events resemble the devastating floods of 2024, underscoring that the region remains highly susceptible to the impacts of these meteorological phenomena.