Rainfall trends in semi-arid cereal regions of Algeria

الملخص EN

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.