Résumé
Bouregreg watershed belongs to the favourable ecological zone of Morocco's central northwest plateau. This watershed is a rainfed area that is marginal for cereal cutivation. Also, this zone belongs to the favourable pastoral areas of that kingdom. The country, like the whole of the Maghreb, since the mid-1970s and beginning of the 1980s, has had more random rainfall conditions. These rainfall changes are marked by substantial declines and greater recurrence of droughts. This study highlights the nature of the spatio temporal phytomass dynamics in this rainfall crisis, in the watershed from 1982 to 2009. From statistics of time series of NDVI pixel values of NOAA images for this period, the study finds a sharp decline in vegetation during the summers. But regression analysis between the rainfall and vegetation finds instead an impact of the rainfall on the wet seasons. It leads to the conclusion that factors other than precipitation are responsible for the sharp decline in vegetation.