Along the French Mediterranean Coast, floods are causing more and more damages although statistical analysis of river peak flows did not show a significant trend. A first cause is the increase of economical value but other climatic factors should be studied. In the case of the 2000 flood in the centre of the city of Marseilles, the rivers have disappeared inside the city and run off associated to flow in the streets are the visible features of the flood. A first cause of the rapid flooding is the lack of infiltration in the soils, which reaches more than 80% of the basin. A second cause may be the more intense rainfalls that influence directly the water depths in the streets due to the short time of concentration of the flows: half an hour to one hour. With such rapid flows (slopes are often steeper than 10%), the distribution of rainfalls has also an influence. Near the harbour (Vieux Port), the sea level can also reinforce the damages. Looking at the second case of the lower Agly flood plain, protected by levees from the extreme floods, other factors can be emphasized. Of course, sea level rise will change the drainage conditions both to the sea and to the coastal lakes of which the level adjusts to the sea level. This high sea level is often accentuated by the wind that comes from East during extreme flood events and thus prevents the flow of the river going from West to East to evacuate into the sea. The sediment and vegetation carried by the flow tends also to raise the water level. For a 100 year flood such as the one of November 1999, this high water level between the dikes, can lead to overtopping, which can destroy houses in the near field. For both cases, numerical models solving 2-D shallow water equations are used to evaluate the relative influence of all these parameters. In the centre of the city of Marseilles, the flow is concentrated in the streets; also, because the flash flood in 2000 passed through most of the area in a few minutes, water cannot enter the buildings. In the Agly case, most of the flow remains in the main channel but the pattern of the drainage network is very important when water invades the flood plain. A right estimate of the roughness is thus essential to estimate the peak water elevation. Moreover, the uncertainty due to climate change trends can lead to an increased risk above all when the safety of the inhabitants relies on the protection by levees.