This study relates to the interaction between the rainfall, the inflow of water and the storage management of reservoirs in semi-arid zones. It consists on studying and analyzing the behaviour of the hydro meteorological variables on the level of the catchment area of Siliana, in Tunisia. The concerned basin is characterized by a wet and cold climate in winter, dryness and heat in summer. It was the subject of several development works (benches, little lakes and two big dams). The measures carried out are made on the basis of a package of observed data on the different sites of reservoirs, collected from the DGBGTH of the Ministry of Agriculture and Hydraulic Resources Hydrological Books. Precipitations during the last decades were lower than the normal on the whole country. The rainfall shortage in Siliana area is about 30 percent or even more. It is probable that this downward trend is explained partly by the climate change. Indeed, we noticed an increase in the temperature and evaporation on the level of reserves of the Siliana and Lakhmess reservoirs. The rainfall deficit is reflected on the flows of the rivers and consequently on the reservoirs inflows. This situation requires vigilance on the state of the water resources and rigor on the level of their management in order to satisfy the requirements of water for the irrigated perimeters downstream of these reservoirs. The consequences of drought are numerous: rainfall deficit, low rate of reservoirs filling and demand fulfilment of irrigated perimeters. Thus, the inventory control must be made with caution to be able to face the risk of a prolonged drought.

L'objet de ce travail consiste à étudier l'interaction entre les précipitations et les apports d'eau aux barrages dans la région de Siliana située en zone semi-aride. Il s'agit d'analyser l'évolution des variables hydrologiques (pluie et apports) ainsi que la température moyenne journalière. Les données traitées sont collectées auprès de la DG/BTH et le CRDA Siliana. Nous avons observé une décroissance significative des pluies jusqu'en 2001 où la série change de comportement, avec tendance vers la hausse. La température et l'évaporation semblent croître. Le déficit pluviométrique influe beaucoup sur les apports et par conséquent le bilan hydrologique. Dans des conditions de pénurie d'eau ; il est nécessaire de procéder à une gestion rigoureuse pour satisfaire les demandes en eau et atténuer les impacts de la sécheresse.