Drainage Basin Characteristics

• Physiographic patterns show a narrow coastal plain, occasionally widened by river deltas, and a series of mountain ranges roughly parallel to the coastline and separated by undulating plains.

• Climate presents mild winters and warm summers, with a warming trend observed in the 1990s. Precipitation values oscillate around 500-700 mm a year, although means and averages make little sense in front of strong inter-annual and intra-annual variations.

• Population trends parallel the recent history of Mediterranean cities. That is, rural migration and concentration of population in large cities until approximately the mid 1970s, and the reverse processes in the 1980s and 1990s. Thus, from centralized compact urban forms and functions, the Barcelona region is undergoing a more dispersed pattern with an increasing presence of features of what we call the diffuse city (or "American model"): low density housing, a communications network built for private transportation, and proliferation of metropolitan subcentres.

Fluvial networks of the Barcelona metropolitan region

Extreme Events

• Floods and droughts are a common characteristic of Mediterranean water cycles. In the Barcelona region, there have been major floods in 1962 (with possibly 1 000 people dead), 1971, 1988 and 1994. Local flashflooding is becoming increasingly important, especially in the rapidly growing coastal plains north and south of the city. Diffuse inondation after storms with intensities of 200 mm/day or more is also becoming common.

• Drought conditions have become also more frequent in the 1990s. In 1990, for instance, the region barely escaped the imposition of supply restrictions. The winter of 1999-2000 has been in many localities the driest winter of the century although, in accordance with the Mediterranean climate, the following spring has been one of the wettest of the last decade