In Spain, drought risk touches every corner, though its grip shifts with location and season. Across the Iberian Peninsula, rainfall varies hugely: humid Spain can average around 3,000 mm annually, while the driest areas register under 200 mm. Those disparities mean that even in a single year, droughts hit some places much harder than others. The number of rainy days also swings dramatically from one observatory to another—well over 180 days in parts of the Bay of Biscay, and fewer than 30 days in the Southeast, between Tiñoso and Cape Gata. The Southeast is also a familiar focus of prayers for rain, moving through phrases that petition for wet weather to end the drought. When drought is described in absolute or relative terms, a datum from one location may not apply to another. The word itself carries multiple meanings and traces its roots to Latin, from the verb sicco, meaning to dry. Siccitas can mean drought, moisture deficit, or dryness; it even appears in the language of Cicero. The Academy defines it as prolonged dry air. With this, the idea of a dry spell becomes a matter of both the presence of dry air and its duration, not just the lack of rain. It is useful to understand drought in weather terms as the absence or reduction of precipitation in both amount and duration, enough to cause significant losses and hardships where it occurs, even affecting food production. This issue is heavily influenced by infrastructure: during a severe Iberian drought, shortages can ripple along the Cantabrian coast with supply constraints that may not spread to North and South Africa. The Southeast, sheltered by the Taibilla Canal network, shows how local systems shape impact. A reminder of historical context comes from the Rabasa-Phenols-Amadorio Transmission described by the Water Consortium in Marina Baja, recalling 1969 restrictions and the 1978 naval transfer to Benidorm. Forest fires also show uneven patterns—drought paired with high temperatures raises risk, but well-kept, clean forests with uniform conditions drastically reduce the chance of large-scale fires. These quick snapshots illustrate that drought manifests differently across Spain and that its causes vary by region.
Beyond the dry and temperate oceanic climates, a long-standing mistake—rooted in French usage—is to call the rest of the Iberian Peninsula Mediterranean, lumping it together with temperate dry-summer zones as if Mediterranean means the same across the board. Dry summers in this region are better described as a subtropical feature rather than a purely Mediterranean one. That distinction is shared with other parts of the world, such as California, central Chile, the Cape region of South Africa, and southwestern Australia. In the Iberian Peninsula, dry-summer temperate climates include inland zones and areas influenced by Atlantic weather, in addition to true Mediterranean zones. True Mediterranean climates hug a coastline and a narrow coastal strip along the sea, not extending far inland. Reaching from the coast to a point like Alto Vinalopó is enough to illustrate continentalization, which becomes clear as winter tightens. Precipitation mainly comes from Atlantic systems in most of the peninsula, while the eastern and southeastern coasts depend more on Mediterranean patterns. The first sector is driven largely by Atlantic storms and disturbances riding the general circulation of a hot jet stream; the second part’s rainfall winds originate from the east, bringing humid air and rain when conditions allow. Pluviometric mechanisms thus differ—Atlantic-dominated systems are less active in the Iberian Southeast—and drought patterns and low-frequency variability follow distinct paths.
There is documented evidence of a long-standing drought duality in the Iberian Southeast. Orihuela and Viciana noted in the 16th century that wheat could be harvested despite drought in Orihuela because irrigation from runoff in the Segura basin sustained fields in Vega Baja. Conversely, when Mediterranean aridity overlaps with Atlantic hydrological drought, conditions can become dire. The era of scarcity is clearly marked in Segura records, such as the early 1800s when fields lay fallow for years due to lack of rain, and notable dryness in 1815 when the Segura ran dry in summer and autumn. The 2013–2014 hydrological year saw dryness in the Precoastal Depression and nearby areas, yet reservoir volumes in Fuensanta and Cenajo in the upper Segura sub-basin exceeded three-quarters of capacity. Later, at the start of the 2016–2017 year, some reservoirs like Guadalest and Amadorio rose with ample reserves, while others faced shortages. The contrast between the parched Iberian Southeast and the Humid Spanish lands with constraints on use and timing shows how complex water supply can be, including tanker shipments or even maritime transport to urban centers like Bilbao and Bermeo during periods of stress.
Understanding these contrasting pluviometric patterns requires looking at two low-frequency teleconnection patterns that influence regional rainfall. The Segura basin is affected by structural patterns such as the North Atlantic Oscillation (NAO) and the Western Mediterranean Oscillation (WeMO). Each pattern relies on an atmospheric pressure dipole. The NAO describes pressure differences between the Azores high and Icelandic low, with its index measured between Azores and Iceland. A negative NAOi indicates more Atlantic storm activity reaching the Iberian Peninsula, while a positive NAOi suppresses storm passage and tends toward drier, clearer conditions. Prolonged positive NAO phases often align with drought on the peninsula. However, Martin Vidéur pointed out that NAO alone cannot explain all regional rainfall, especially in the southeastern front where westerly winds from the east play a key role on precipitation in Las Vegas Media and Vega Baja. This observation led to the WeMO concept, defined by the pressure difference between Cádiz-San Fernando and Padua. WeMOi captures the dipole between the Azores Anticyclone and the Gulf of Genoa low. A positive WeMOi signals westerly winds and drier conditions over Bajo Segura, while a negative WeMOi, with low pressures near Cádiz and a European anticyclone, brings an eastward flow with humidity and rain when conditions permit. The combined influence of extended positive phases of both NAO and WeMO can produce prolonged drought across the peninsula, as seen in the years 1993–1996 when drought persisted with high influence from both oscillations.
Finally, drought does not simply vanish with a hot summer. Mediterranean sea temperatures, by storing heat, raise the risk of subsequent flooding as autumn approaches. Surface wind patterns from the east and the mountain troughs can interact with a DANA type system, maintaining a lingering risk of heavy rainfall events after a dry spell. The interplay of warm seas and persistent atmospheric patterns keeps drought and flood risks tightly linked in the region.