Using Chance Constrained Programming Approach for Optimal Crops Selection and Economic Profitability of Irrigation Under Hydrological Risk: The Case Study of Small Dams in Tunisia

This study aimed to analyze the economic profitability of irrigation under hydrological risk. Towards this end, two hill lakes located in different climatic conditions (sub-humid and semi-arid climates) were selected and a chance constraint linear programming model was used. The model incorporated the uncertainty of water supply at exceedance probability of 80, 90, 95 and 99%. The results showed that in a sub-humid climate, there are 100 and 95% chances to meet monthly water requirements for winter and summer crops, respectively. The impact of a small dam on local farming economic profitability was highly significant. Both environmental and socio-economic objectives can be achieved. In a semi-arid climate, results showed that, at the 90% water supply reliability, only winter crops and olive trees were included in the optimal cropping pattern under deficit irrigation and on a limited area. Summer crops were not recommended. The economic profitability of irrigation around the small dam would be strongly reduced. Therefore, the objective to improve the population well-being in arid and semi-arid regions assigned to these structures is not likely to be achieved. As the public budget allocated to environment protection becomes more and more restraint, this study suggests implementing hill lakes first in areas where their economic and environmental efficiency is proven.