Spanish Catchment Basins: Topography, Rivers, and Rainfall Patterns
Catchment Basins and Features
A whole basin slope catchments discharging into the sea itself. Spain has three sides:
a. Cantabrian
Location: Situated north of the peninsula. Rivers include the Basque, Cantabria, and Galicia, occupying approximately 5% of the peninsula.
Features:
- Length: Short rivers, most originating in the Cantabrian Mountains and flowing into the Cantabrian Sea. Galician rivers are longer, flowing into the Atlantic. The short distance between the headwaters and the mouth results in a steep, hilly course.
- Flow: Influenced by factors such as mountains, rain, and snow. They have a relatively high flow rate (20 l/s/km2), but the absolute flow is modest due to their short length and small basins. Maximum flow occurs in fall and winter, with a minimum in summer. Rivers are generally more regular in Spain.
b. Atlantic Watershed
Location: Occupies 65% of the peninsula. Most rivers in this watershed run through the central plateau and the Guadalquivir depression.
Features:
- Length: Rivers originating near the Mediterranean Sea (S. Iberian) and flowing into the Atlantic have a long journey. Watersheds are often extensive.
- Flow: The absolute flow is usually significant due to the large river expanse, but it is always less than 20 l/s/km2. The Mediterranean climate leads to irregular flow patterns. Maximum flow occurs in February and March, with a minimum in summer.
- Erosive Capacity: Not prominent, as they have delivered relief to save.
c. Mediterranean Watershed
Location: Occupies 30% of the peninsula. It is located in the east and southeast.
Characteristics:
- Rivers are short, except for the Ebro, due to the proximity of mountain ranges and the sea. Basins are small and fragmented, except for the Ebro.
- Erosive capacity is very high due to steep slopes and, in some areas, the absence of adequate forest cover.
- Flow: Irregular, with some rivers disappearing in the summer due to low rainfall in the arid southeast. Most rivers have a Levantine Mediterranean fluvial regime, with high flow in autumn due to frequent cold fronts. In the southeast, there are seasonal courses rather than true rivers.
Watershed Mountain Ranges and Rivers
The Massif Galician and Cantabrian Mountains: Divide the waters of Biscay and the Atlantic. Galician Massif rivers include the Tambre, Minho, and Eo. The most important is the Minho, originating in the Sierra de Meira and flowing into the Guard, bordering Portugal. Its principal tributary is the Sil.
Rivers of the Cantabrian Mountains include the Nalón, Sella, Nervión, Bidasoa, and Ebro. The Ebro originates in Fontibre and flows into a delta in Amposta. Its major tributaries from the Pyrenees are the Aragón, Cinca, Gallego, and Segre.
Sistema Ibérico: Divides the waters of the Mediterranean and Atlantic. Important rivers include the Mijares, Júcar, Duero, Tajo, and Guadiana.
- Duero: Originates in the Urbión Mountains. Major right-bank tributaries from the Cantabrian Mountains include the Pisuerga, Elsa, and Arlanza. Left-bank tributaries include the Adaja, Eresma, and Tormes.
- Tajo: Originates in the Universal Mounts on the Sierra de Albarracín and ends in Lisbon. Tributaries from the Central System include the Jarama, Guadarrama, Alberche, Tiétar, and Alagón. Tributaries from the Montes de Toledo have low flow (Almonte and Salor).
- Guadiana: Has a karstic origin, starting at the spring of Pinilla near Ruidera. It disappears downstream due to groundwater circulation and re-emerges at a karst resurgence (the Ojos del Guadiana). Right-bank tributaries include the Cigüela, which feeds the Coldstream lagoon system and Záncara tables. Left-bank tributaries include the Zújar and Jabalón. It flows into Ayamonte.
Betic Systems: Divide the Mediterranean Sea and the Bay of Biscay. Important rivers include the Safe, Guadalete, and Guadalquivir.
- Guadalquivir: Originates in the Sierra de Cazorla and flows into Sanlúcar de Barrameda. Right-bank tributaries have low flow, including the Gualimar, Jandula, Guadiato, and Bembézar (originating in Sierra Morena). The left-bank tributary Genil has abundant flow, originating in Sierra Nevada.
Relationship Between Topography and Rainfall Distribution
Geographical Factors:
Latitude: Spain is in the northern hemisphere’s temperate zone, resulting in four thermal seasons (summer, autumn, winter, spring). This influences the water balance, as different seasons have varying rainfall patterns.
Situation: Spain’s location at a crossroads of air masses with different characteristics, between two bodies of water with different thermal properties, affects moisture patterns. This leads to variations in rainfall and river basin water volume.
Influence of the Sea: The sea’s influence is limited in Spain due to mountainous terrain parallel to the coast, the peninsula’s width, and the relatively unindented coastline. This limits the sea’s influence on the interior.
Relief and Disposition:
- Mountain systems along the coast (Cantabrian Mountains, Catalan Coastal Range, Betic Cordillera) inhibit the sea’s influence.
- The Ebro and Guadalquivir depressions are enclosed by mountain ranges, deepening the isolation of the Ebro basin. The Guadalquivir depression receives some sea influence in the southeast.
- The Duero depression is also isolated by the relief, resulting in limited rainfall and frequent fogs due to stagnant air.