Socio-hydrological drivers of agricultural water use in small reservoirs

International audienceMillions of small reservoirs built across semi-arid areas present a potential to support agricultural livelihoods of rural smallholders. The scale and geographical dispersion of these multiple lakes restrict the understanding of these coupled human-water systems and the identification of adequate strategies to support riparian farmers. This research developed a multi-scalar interdisciplinary approach to characterise the hydrological and wider drivers of agricultural water use around multiple small reservoirs in semi-arid central Tunisia. The combination of field surveys, quantitative questionnaires and qualitative, semi-structured interviews confirmed minimal withdrawals, but highlighted the diversification of practices, the rise in fruit farming and peripheral benefits generated here by the development of 56 lakes. 48% of lakes provide residual benefits for the occasional watering of on average 300 fruit trees and support to downstream wells exploited for irrigation. A further 13 lakes (23%) provide high levels of benefits (900 fruit trees each), albeit with low equity, supporting essentially established farmers. The analysis of surface water assessments every 8 days from Landsat 5-8 imagery over 1999-2014, provides unprecedented insights into the significant water scarcity and unreliability that impedes agricultural intensification on 86% of small lakes. Limited storage capacities and prolonged droughts highlight the need for small reservoirs in this climatic context to retain a supplementary irrigation objective and not strive to support widespread intensification of irrigated practices. Many farmers lack the capabilities to increase their withdrawals and suffer physical and economic water access difficulties, mismanagement, compounded through limited and short-term government assistance. Individual successes resulted from farmers' economic resilience and means to secure alternate water supplies during dry spells