2.1.1. The Case Study of Barcelona

Barcelona (Figure 1) has an extension of approximately 100 km2, 1,619,000 inhabitants and it is highly urbanized. An important part of its urban development lies in a flat area up to few tens of meters above mean sea level. The city faces the Mediterranean Sea and approximately half of its coast line is occupied by the harbor and the remaining by sandy beaches. In the opposite side of the sea, there are hills with significant slopes towards the urban area. The great majority of the drainage system is a combined one and Barcelona experiences urban pluvial floods due to intense rainfalls, steep slopes towards the flat urban area, high degree of imperviousness and, in recent years, expansion of new urban areas draining into an older drainage system. The mean annual rainfall is 612 mm/y, the degree of imperviousness is estimated to be approximately 70% of the whole municipal area even though it can reach much higher percentages in the urban areas (see for instance the two zoom-in areas in Figure 1). The city also experiences Combined Sewer Overflows (CSO) that generally occur during rainfall events larger than a few millimeters. CSOs pollute the river Besos (that coincides with the north-eastern boundary of the municipal area shown in Figure 1) and the sea water both in front of the beaches and in the harbor. Figure 1 also shows the planned GI that will be described in Section 2.2.1.

**Figure 1.** Plan view of Barcelona with all the planned GI: ponds, green roofs and bioretention cells. The colored lines show the classification of five different kind of streets where bioretention cells are planned (a different spatial allocation of bioretention cells was proposed as a function of the different street slope and width).
