Multi-method assessment of reservoir effects on hydrological droughts in an arid region

Abstract. Increasing pressures on water resources in arid regions have led to their increased management and construction of dams; however, the impacts of these anthropogenic activities on hydrological droughts have yet to be incorporated and assessed. Here, the impact of the Santa Juana dam on hydrological drought characteristics downstream has been analysed in the Huasco basin in northern Chile. Two different methods of drought analysis, threshold level method and standardised indices, were applied to observed and modelled data. An upstream-downstream approach was taken for the observation data, analysing the "disturbed" (post-dam) period and the "undisturbed" (pre-dam) period to allow for an assessment of the onset of the significant anthropogenic activity on the hydrological regime. Modelled data from the Water Evaluation And Planning (WEAP) model generated a naturalised scenario and human-influenced scenario for similar analysis. Our findings show the characteristics of recent drought events in the basin (1965–2013). The reservoir is shown to help alleviate hydrological droughts by reducing frequency, duration and intensity of drought events, though it did not alleviate major multi-year drought events. A delay in timing of drought events has been observed also with the presence of the dam. The reliability of these different methods and approaches to quantify the impact of the dam are evaluated, with concluding recommendations that the threshold level method using an undisturbed threshold may be the most suitable. These findings show an applicable way forward with quantifying the human influence on hydrological droughts, a method that can be applied elsewhere, and on other human activities.