Water use efficiency in an arid watershed: a case study

Integrated Water Resource Management (IWRM) becomes increasingly important in arid watersheds, where water resources arescarce and demands are rising under increased population pressure. In this case study, we present the results from the Elqui Valleyin Chile, where water resources are shared between agriculture, mining operations, hydropower generation and drinking water fornearby cities. An IWRM model was applied to visualize water resources distribution in the catchment and determine irrigation andwater use efficiencies. After calibration with observed surface and groundwater measurements, the model showed large differencesin efficiencies between different irrigation sectors. Most notably, irrigation sectors with the highest irrigation security, i.e.,higher water rights per hectare, were characterized with lower water use efficiencies. Frequent water deficits were present in sectorsdownstream of the main reservoir, which was related to limited water rights per hectare, lower irrigation efficiencies andhigher water demands due to larger agricultural areas. In subsequent scenario analyses, the model was used to evaluate the impactof improved irrigation and water use efficiencies in these downstream sectors, to confirm an important reduction in water deficits,except for drought years when surface water resources are insufficient. In a third scenario, groundwater resources were allowed tocompensate for water deficits, effectively reducing these in most irrigation sectors, especially during droughts. Expansion of thecurrent agricultural area by 37% was evaluated, as a future scenario, and was found to be unsustainable, as aquifer levels are loweredto such levels that make annual recharge insufficient.