During the last decade , the issue of climate change has been recognized as one of the major problems of development at local and regional level and even internationally , alongside sustainable development , preservation and the protection of the environment. To try to solve this problem, it is essential to analyze the prior term precipitation. We tried to answer some basic questions and concern, among others: \nHow to evaluate the rainfall in our region in space?\nWill he reduce rainfall during the last decade?\n In this context, we studied the rainfall using statistical processing and analysis of drought indices. The calculation of indices for different stations shows a division of the year into dry and wet season. The North-South development shows that the percentage of dry period varies from 50 % in the North of the wilaya (Ain fares) and 55 % in the South (Ghriss). Years of drought is more remarkable in the regions Ghriss because they succeed for 4 years (1998-2001) , and Fergoug (1996-1999). All these observations allow us to say that we are facing an irregular climate with two dominant seasons. The range of rainfall variation is very large. The extreme can be reached at any time of the year when there is moisture or drought, as the other one can achieve a very high degree of severity. Our region stretches between arid and semi arid the other from the classification of bioclimatic therefore the hydrological response to rainfall events is complex because the influence of different climatic factors such as insulation, temperature, winds.... The irregularity of the seasons has shown us that the climate is not stable and will continue to evolve over time and space.