Effect of intense short rainfall events on coastal water quality parameters from remote sensing data

• Strong rainfall events in small river basins often compromise the quality of coastal waters.
• Parameters of turbidity, total suspended solids and secchi disk depth are retrieved from MODIS.
• Changes in coastal water quality during the bathing season are observed with remote sensing data.
• The spatial and temporal changes of these parameters depend on rainfall intensity and shoreline distance.

Strong rainfall events, especially during summer, in small river basins cause spills in the sea that often compromise the quality of coastal waters. The goal of this paper is then to study the changes of coastal waters quality as a result of intense rainfall events during the bathing season through the use of remote sensing data. These analyses are performed at the outlets of small watersheds which are not usually affected by high sediment transport as in the case of large basins which are persistently affected by intense solid transport which does not allow retrieving a reliable correlation between rainfall events and water quality parameters. Four small watersheds in different Italian regions on the Mediterranean Sea are selected for this study. The remotely sensed parameters of turbidity, total suspend solids and secchi disk depth, are retrieved from MODIS data. Secchi disk depths are also compared to available ground data during the summer seasons between 2003 and 2006 showing good correlations. Then the spatial and temporal changes of these parameters are analyzed after intense short storm events. Increases of turbidity and total suspend solids are found to be around 35 NTU and 20 mg L−1 respectively depending on the intensity of the rainfall event and on the distance from the shoreline. Moreover the recovery of water quality after the rain event is reached after two or three days.