English

Abstract

This study evaluates the ten-day period pluviometry variation in the cereal regions in the north of Algeria, through a period of 73 years (from 1936 to 2009). This variation emphasizes the rainy ten-day period and the dry ones, at the thresholds of rains selected for more than 0, 1, 5, 10, 20 and 30 mm. By extent, the number of the rainy days, their received volumes and their probability to occur are determined. This step relies on the Markov chain of the order 1. The results show a repartition of average pluviometrical quantities, and the number of rainydayper periods of ten days; such a repartition which is irregular and weak in relevance to the increase of the pluviometrical thresholds, on the regional and the national scales. The rain probabilities of occurrence evolve indeed, between 41 and 80%, according to the considered percentages of 20, 30, 50 and 80%. Strong water deficiencies characterize the ten-day periods through the year, which interpret dry sequences in relevance to the resistance of the pluvial cereals to drought of 5, 10, 15 and 20 days. Some droughts of ten days reach 60 to 70%, which suit the soil, the seed and germination preparations, and arrive to 90% during the formation and the maturation of the cereal grains. Water deficiency is noticed, compared with the cereals needs during the yield accomplishment; whatever are the dates of the practiced sowing, from the East to the West of the country.   Key words: Algeria, pluviometry, water deficiency, drought, cereals, sowing.