This study explores the regionalisation of annual rainfall in northern Algeria, a crucial region for rainfed cereal growing, in a context of climate change. The objective is to highlight the effect of rainfall variability, which regularly impacts agricultural production. The methodology is based on rainfall data (1940–2017) from 76 weather stations. The kriging method, a geostatistical technique, is used to interpolate the data and map isohyets. The results are compared with earlier periods (1913–1938) to assess climate trends. The results show a decreasing rainfall gradient from east to west, with rainfall varying from 1,050 mm to 100 mm annually. Wetlands (16% of the country) are shrinking, while drylands (84%) are expanding. Rainfed cereal growing, although mainly located in areas with rainfall deficits, is benefiting from improved farming practices that partially compensate for climatic constraints. Regionalisation highlights rainfall heterogeneity and its evolution, underscoring the need to strengthen the network of weather stations for optimal management of climate hazards and water resources for better planning, cereals.