If the scarcity of water resources and their limitation is a characteristic of the climate of Morocco, this phenomenon seems to know a distinct accentuation during the last decades. But, on the other hand, the scarcity of this resource and the drought are the main constraints of agricultural production; the situation then is more alarming. Although scientists in the region have developed many technologies to cope with these environmental problems, the difference between the yields achievable by farmers and the potential yields generally remains huge in rainfed and irrigated areas.This paper develops the problem of rainfed agriculture in the Khemisset region, El Ganzra site, in the constraining context of climate change and natural resources degradation. Indeed, several measures are necessary to cope with these climate changes; therefore, we propose a method of agro-climatic analysis of the first significant rains. Our investigations, which are part of the decision support approach, are based on choosing the suitable period for sowing cereals using the "InStat" tool. The method used is based on a quantitative approach, allowing us to study the Spatio-temporal variability of precipitation and the analysis of drought intensity on the site. Consequently, the modelling makes it possible to propose scenarios to farmers regarding sowing dates and crop selection at the appropriate time.