Abstract
The study focuses on rainfall, number of rainy days and droughts, on an annual time step basis, over the period (1940-2019). Each parameter is analysed by the average behavior of 1,817 variables representative of 23 semi-arid wilayas. The approach helps to characterise the rainfall climate of cereal-growing regions, where production and yields per hectare are unstable for decades.The average rainfall, estimated at 423 mm, shows a cyclical evolution, reflected by a change in averages: 430, 405, 440 mm. These averages reproduce two relatively rainy cycles (1940-1970) and (2000-2019), separated by a dry cycle (1970-2000). The frequency of cyclical rains, however, shows that rains above 400 mm remain less dominant over 79 years. The averages of observations decrease progressively with the increase of the quantities of rains, that is to say, percentages that do not exceed 14, 13 and 9%. These characteristics underline interannual droughts, which fluctuate between 0.8 and -2.5, showing a progressively decreasing number of rainy days. The results obtained do not seem to explain all the variations in cereal production and yield. However, the correlation coefficients below 35% reflect the efficient use of rainfall during the crop growth cycle, which is subject to other production factors.
Highlights
Agriculture in Algeria remains the mainstay of the country‟s economy, providing nearly 60% of jobs, in rural areas [1,2]
The interquartile range (IQ), 222 mm, denotes rainfall variability, the calculated standard deviation of which reflects the dispersion of values around the mean
According to the coefficient of variation, the variability in the study regions reaches 41%, which is higher than the figure defined (30%) by [27], Hoff and Rambal (2007), for the Mediterranean isoclimatic regions
Summary
Agriculture in Algeria remains the mainstay of the country‟s economy, providing nearly 60% of jobs, in rural areas [1,2] These regions, which belong for the most part to the territory classified as semi-arid, mark the eastern and western plains of the country, dominated by extensive rain-fed cereal cultivation. In Algeria, studies relating [11,12,13] to the evolution of rainfall, associated with water deficits or droughts in relation to cereal growing, are very rare Their interests are all the more important in this context marked by climate change and the rise in the price of cereal products. This research recommends an analysis of these parameters over a 79-year history, on the scale of the semi-arid regions of Algeria
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