RAINFALL AND CYCLICITY IN SOUTH-WESTERN SAUDI ARABIA BETWEEN 1987-2017

South-west Saudi Arabia represents a physio-climatic duality. Indeed, this space is composed of two opposing spaces. The first western, bordering the red sea, higher and relatively humid, while the second eastern. At the edge of the Rub El-Khali, lower and drier.The objective of this study is to take stock of this duality by calculating rainfall degrees using the rainfall averages at the three scales, annual, seasonal and monthly for the period 1987-2017 of seven stations representing the two spaces.After statistical, graphical and cartographic processing, it appears that this area, the southwest of Saudi Arabia, is effectively divided into two sub-areas; the eastern part more marked by rainfall and where the non-rainy cycles are longer and more numerous unlike the western part less affected by drought fruit of rainy cycles which are, however, short and less numerous. This will lead to differential erosion. It is more wind in the east and water in the west. The consequences confirm this duality.