Evapotranspiration, bilan de l'eau et variabilité des précipitations en Tunisie, en relation avec l'agriculture

Abstract

Quatre facteurs climatiques décisifs pour la végétation et l'agriculture tunisienne sont discutés : 1.La moyenne annuelle des précipitations ; 2. L 'evapotranspiration potentielle et le bilan de l'eau; 3. Le nombre de mois humides;. 4. La variabilité interannuelle des précipitations. Le nombre de mois humides indique les mois pendant lesquels les précipitations font augmenter une «evapotranspiration potentielle du paysage réel». Elle est basée sur la végétation réelle; l'évapotranspiration potentielle, par contre, telle qu'elle a été calculée jusqu'ici, part de la supposition d'une répartition absolument égale et dense de la végétation.

Contrasting water management techniques in Tunisia: towards sustainable agricultural use

“…Rainfall is highest over the crest of the plateau due to altitudinal forcing, and it decreases towards the low‐lying plains (Golany 1988). Actual evapotranspirative losses vary between 400 and 500 mm per annum resulting in a negative annual water budget of 200–300 mm (Frankenberg 1980). Although the altitude of the plateau generates some cooling, summer temperatures frequently exceed 40°C, moderating to a seasonal average of 20°C during winter (Henia 1988).…”

“…These mountains give way to the Plain of Kairouan in the east, which stands at an altitude of 200–400 m and is covered in well‐stratified alluvial Miocene and Pliocene (clay–sand) deposits. Rainfall across the region is higher than in the south, varying between 200 and 350 mm per year, but temperatures attain 35°C in summer and actual evapotranspirative losses reach 600–700 mm per year, resulting in a negative annual water balance of between 300 and 400 mm (Frankenberg 1980; Guillaud and Trabelsi 1991). The vegetation is grazed semi‐arid steppe, characterized by herbs and dwarf shrubs.…”

“…The scale of the hydraulic works renders adaptive response to extreme events difficult. The structures must be sufficient to withstand high‐magnitude events from the outset, but predicting the vagaries of this marginal environment, where inter‐annual variability of precipitation ranges between 30 and 40% (Frankenberg 1980), is notoriously difficult.…”