Polders in Spain

Spain is known as a dry and warm country. Three main climate types can be distinguished. Much of the country has a Mediterranean climate, characterized by warm and dry summers. It is predominant along the Mediterranean Sea and the southern Atlantic coast, and inland throughout Andalusia, Extremadura, and most of the Central Region.

In the southeastern part of the country, but also widespread in other parts, a semi-arid climate predominates. This zone covers most of the Region of Murcia, Southern Valencia, and Eastern Andalusia, where a desert climate also occurs in some areas. Further North, a semi-arid climate predominates in the upper and middle parts of the Ebro Valley, which crosses Southern Navarra, Central Aragon, and Western Catalonia. This climate type also occurs in Madrid, Extremadura, Castile-La Mancha, and some areas in Western Andalusia. The dry season lasts longer than the summer.

Finally, Spain has a maritime climate. This climate type is primarily found in the Atlantic Region, in the northern part of the country. It is also found in Northern Navarra, in most of the highlands, and in the valleys of the Pyrenees, where a humid subtropical climate also occurs in some areas. Winter and summer temperatures are influenced by the ocean, and the climate is predominantly dry.

In such climates, agriculture is practically impossible without irrigation. Nevertheless, Spain also has a number of polders. They are primarily located in former marshes – marismas – along the east and south coasts in the valleys and deltas of the Barbate, Douro, Ebro, Guadalquivir, Guadalete, Guadiana, Júcar, Miño, Segura, Tagus, and Turia rivers.

The following polders have been identified. The largest polder area lies between the Ebro Delta and Valencia. There are nine polders with a total area of approximately 33,000 hectares. The Ebro Delta itself covers 20,000 hectares. The delta is subdivided into six polders, each with an area of between two and four thousand hectares. Some of the marshes on the left bank of the Guadalquivir River have been reclaimed. For example, a 28,500 hectare polder lies south of Seville. An area of 4,230 hectares has been reclaimed in the Bay of Cádiz. Furthermore, a 1,500 hectare polder, bearing the beautiful name of Castillo de Dona Blanca, exists along the right bank of the Guadalquivir River. A polder primarily used for industry lies in the Odiel-Tinto marshes.

Finally, the Pego-Oliva polder needs to be mentioned, a polder in the Motril Plain south of Granada, polders in the Guadiana marshes, the Barbate, the Bay of Algeciras, and polders in the Albufera marshes. This brings the total polder area in Spain to at least 215,000 hectares, slightly more than twice the size of Polder Flevoland in the Netherlands. The actual area must be considerably larger, as this is difficult to determine for some polders.

Nearly all polders are used for agricultural purposes. Although they are situated in former marshes, irrigation is still necessary to facilitate agricultural use. Therefore, nearly all polders are equipped with dikes, irrigation, and drainage systems.