Les variations climatiques et les ressources en eau superficielle en zone semi-aride

Abstract

The growth in water needs is through rapid population change, industrial development and extension of agriculture. Northern Algeria experienced variability in annual rainfall during the 20th century. This variability was particularly accentuated from the 1980s and had significant negative impacts on surface water resources, as well as on the rainfall cycle. Our study consists in characterizing the temporal and spatial variability of the chronological series of hydro-climatic parameters (rainfall, flows) at the level of four watersheds of the Highlands of Constantine. ; (Madher, Chemora, Boulefreiss and Foum el Gueiss basins) for 43 years (1969-2012). A preliminary analysis of all the physical and geographical parameters of the selected watersheds was carried out. Then, using statistical trend tests and correlation and spectral analyzes, either increasing or decreasing trends in temperature, precipitation and flow were observed. A better understanding of the relationship between climate change and its impacts on the availability of water resources requires an analysis of trends on series of temperatures, precipitations and flows. This is what we have done, over a long period, for the basins. The results of this evaluation show a significant decrease in annual precipitation ranging from 19 to 54.8% and an increase in average temperature of 0.7 °C at over the past 20 years. This has enabled us to specify the evolution of rainfall over the past decades and the trends that can be detected there. The break detection study made it possible to locate a change in the rainfall regime for most of the rainfall stations studied. The application of the statistical tests to the seasonal rains, allowed us to conclude that it was the winter and spring rains that recorded a break in the time series. On a monthly basis, we noticed that it was the months of the two rainy seasons that recorded the most significant and most significant decreases, especially the months of: December, January, March and April. The hydrological study, which is based on the statistical processing of hydrometric data, shed light on the fundamental aspects of annual and seasonal flow, and therefore of surface water resources and their variability. The values of the coefficients of variation of the internal intakes are relatively high, which indicates an irregular regime. This irregularity is more acute in the east. In terms of hydraulics, these wadis are characterized by a violent and rapid flow. Finally, we looked for the links between this rainfall and hydrological variability with climatic fluctuations materialized by different climatic indices, NAO, MO.The study approach is based on the statistical treatment of time series linked to spatiotemporal dimensions by the method of spectral analyzes adapted to the study of stationary processes (continuous wavelet analysis, wavelet coherence analysis).