Temporal evolution of urban growth and its impact on runoff rates generation

Abstract

The province of Alicante (SE Spain) is the fourth most populated region in Spain, with 1.9 million inhabitants. Additionally, tourism is one of the most important industries of the region since the sixties of the last century. Tourism industry attracts more than 3.4 million tourists and 14.5 million overnight stays per year, mainly in summer. Urban development has expanded as a consequence of that demographic pressure, mainly in the coastal areas. At present time, there are examples of watersheds with ephemeral streams where more than half of the complete area is occupied by urban soil. This urban development has increased the existing high hydrological hazard, since the hydrological answer of watersheds to a precipitation event has moved to higher flow rate peaks and shorter concentration times. Urban planning policy makers have to face that problem urgently since the main climate features of this geographic area are the very intense and localized rainfalls, which fall specially in the months of September, October and November. Then, the ravines beds, which remain dry during the majority of the year, are forced to lead high amounts of water in a clear case of flash floods. In the present study, we analyse the temporal evolution of the hydrological response of a small watershed as a consequence of the urban growth. Hydrological dynamics were accomplished with the ArcGIS tool and the SWAT hydrological model. Changes in soil uses have been analysed through GIS- based tools, with soil use coverage information for the different study periods. Main results show that study area (Amerador watershed) has duplicated its urban area since 1990 (31.62 ha) to 2012 (61.07 ha) increasing the risk of flooding in a coast urban zone with low runoff thresholds (0 l/m2–7.5 l/m2) and discharges that reach 190 m3/s.