Contenu du sommaire : Sécheresse

The 1976 drought in îhe Rhône-Alpes country (France). The exceptional drought of the year 1976, is noteworthy by its duration between 5 to 7 months and by its intensity : Lyon-Bron received 30 % of the normal precipitation between March and June. However the drought's intensi y varied with a strong diminution from North to South.

The 1976 Spring drought and heat had hydrological consequences in the Northern Alps which are interesting to be studied because of their variety. The deficiency of the pluviométrie totals from december 1975 to june 1976 (the lowest ever recorded) caused the lowest wafer levels ever observed in may average monthly discharge and june for pluvial supplied streams = 0,20). 1976 monthly discharge As the snow cover was thinner than usual because of less important snow falls, the deficiency of the discharge for the snow supplied streams was rather high (0,50 to 0,60 of the usual monthly discharge). The peak value of the monthly average flows occurred in may and not in june due to the early heavy heat. This one and this exceptional daily insolation from may 1st to june 24th (50 % days had more than 11 hours of sun) caused surplus discharges in may (1,20 to 1,68 of the normal value) for high altitude streams (having more than 20 % of glacier area in the river-bassin) .

According to the datas of the year 1976, there is not direct correlation between drought and forest fires. The main propagation's factor is man's intervention by imprudence or negligence. In fact, these dealings are always bound to derelict places, characterized by social and spatial desorganisation.

In oceanic climates, drought may be defined as a deficiency of evaporation. Applied to Brittany, this method of investigation šhotvs that a serious drought such as that of 1976 occurs about four times a century, and that drought years are relatively frequent. The phenomenon is all the more strongly felt for this region's increasing specialization in pasturage.

The three irrigated regions, the Haouz of Marrakech, the oasis of Ispahan, end the huertas of South Eastearn Spain, belong to arid or subarid mediterranean areas. Thus, rivers and water-tables are of vital importance. Water tapped from rivers or tables permitted early development of intensive farming. Each of these three regions is an ensemble unique in many respects. However agrarian organization obeys similar patterns and rules in all three : 1°) from upstream to downstream, the intensity of farming decreases in proportion to water ressources. This gradient of irrigation tends to fade out in the places where modern hydraulic engineering increased usable water sources ; 2°) this halo organization of the rural landscape is more or less obscured by certain anomalies, inconsistencies, resulting from the contingencies of a complex land history. In fact, these anomalies, in so far as they seem to reappear in all huertas are the tangible translation into the rural landscapes of conflicts concerning water appropriation (on the one hand) and of the stages of development of irrigated areas {on the other) ; this development is characterized by the succession of generations of great estates whose owners charged the peasant communities for use of water and land. The repetition of these patterns of organization suggests a « huerta theory » issuing from the scarcity of water and the stakes involved in its exploitation.

Cyprus suffred in 1972-73 the worst drought ever registered since the beginning of meteorological observations in the island. This drought did not affect the island's economy and its population's standards of living as did the previous ones which are known through history : Cyprus enjoys nonadays better equipments and has easy external trade relations. With a special reference to the irrigated area of Morfou it is stressed that the local aquifers may be destroyed by over extraction because the boom of oranges' and grapefruits' cultivation was quicker than the implementation of a comprehensive plan prepared to enlarge the water shed and increase the aquifers' inputs : such a discrepancy may destroy the ecological balance.