Land cover changes, autumn rainfall and soil vulnarabilities in the Bouregreg watershed in Morocco
The Bouregreg watershed is located in the Rabat-Salé-Zemour Region in Morocco. It is a pastoral area in the interior mountainous parts and agro-pastoral in the plains. Like most watersheds of Atlantic Morocco, the landscape dynamics observed in the Bouregreg watershed are marked by an intensification of agricultural areas in the plains and their extension to the slopes. Indeed, land cover supervised classification using Landsat images around 1987 and 2006 indicate land cover changes in the Bouregreg watershed. Between 1987 and 2006, over the entire watershed, 15% of the wooded areas have been converted into agricultural areas. When taking the morphology of the watershed into account, the study shows the fragility of these agricultural areas. Indeed, 30% of the cultivated areas are located on slopes from 5 to 10%, and 24% on slopes from 10 to 20%. These croplands exhibit almost no vegetation during land preparation and planting. The archiving and seasonal monitoring of variations in the Normalized Difference Vegetation Index (NDVI), derived from the SPOT vegetation sensor for the period from 2001 to 2009, reveal at the beginning and end of growing seasons, a lengthening of the period during which the soil is almost bare during the years of exceptional drought. In addition, analysis of the rainfall time series at the Rabat meteorological station shows a modification of autumn rainfall regime since 1999, with an increasing trend specifically during October. This situation is likely to make the bare soil on steep slopes vulnerable to erosion by rain especially during particularly dry years like 2003 and 2007.