Preprints
https://doi.org/10.5194/hess-2023-246
https://doi.org/10.5194/hess-2023-246
24 Oct 2023
 | 24 Oct 2023
Status: a revised version of this preprint is currently under review for the journal HESS.

The influence of human activities on streamflow reductions during the megadrought in Central Chile

Nicolás Alamos, Camila Alvarez-Garreton, Ariel Muñoz, and Alvaro González-Reyes

Abstract. Central Chile has experienced a protracted megadrought since 2010 (up to date), with annual precipitation deficits ranging from 25 % to 70 %. Drought propagation has been intensified during this time, with streamflow reductions up to 30 % larger than those expected from historical records. This intensification has been attributed to the cumulative effect of precipitation deficits associated to catchment memory in near-natural basins of central Chile. However, the additional effect of water extractions on drought intensification in disturbed basins remains an open challenge. In this study, we assess the effects of climate and water use on streamflow reductions during the last three decades in four major agricultural basins in central Chile, with particular focus on the ongoing megadrought. We address this by contrasting streamflow observations with near-natural streamflow simulations representing the discharge that would have occurred without water extractions. Near-natural streamflow estimations are obtained from rainfall-runoff models trained over a reference period with low human intervention (1960–1988). We characterise hydrological droughts driven by precipitation and human activities during the evaluation period (1988–2020) in terms of the frequency, duration and intensity of near-natural and observed seasonal streamflow deficits, respectively.

Our results show that before the megadrought onset (1988–2009), streamflow in the four basins was 2 to 20 % lower than the streamflow during the undisturbed period. Between 81 to 100 % of these larger deficits were explained by water extractions. During the megadrought (2010–2020), streamflow was reduced in a range of 47 to 76 % among the different basins, compared to the reference period. During this time, the climatic contribution to streamflow reductions increased and had a lower relative contribution, accounting for 27 to 51 % of streamflow reduction. During the complete evaluation period, human activities have amplified the propagation of droughts, with more than double the frequency, duration, and intensity of hydrological droughts in some basins, compared to those expected by precipitation deficits only. We conclude that while the primary cause of streamflow reductions during the megadrought has been the lack of precipitation, water uses have not diminished during this time, causing an exacerbation of the hydrological drought conditions and aggravating their impacts on human water consumption, economic activities, and natural ecosystems.

Nicolás Alamos, Camila Alvarez-Garreton, Ariel Muñoz, and Alvaro González-Reyes

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on hess-2023-246', Anonymous Referee #1, 28 Nov 2023
    • AC1: 'Reply on RC1', Nicolás Alamos, 17 Jan 2024
  • RC2: 'Comment on hess-2023-246', Anonymous Referee #2, 13 Dec 2023
    • AC1: 'Reply on RC1', Nicolás Alamos, 17 Jan 2024
  • RC3: 'Comment on hess-2023-246', Anonymous Referee #3, 14 Dec 2023
    • AC1: 'Reply on RC1', Nicolás Alamos, 17 Jan 2024
  • AC2: 'Comment on hess-2023-246', Nicolás Alamos, 18 Jan 2024
Nicolás Alamos, Camila Alvarez-Garreton, Ariel Muñoz, and Alvaro González-Reyes
Nicolás Alamos, Camila Alvarez-Garreton, Ariel Muñoz, and Alvaro González-Reyes

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Short summary
In this study, we assess the effects of climate and water use on streamflow reductions and drought intensification during the last three decades in central Chile.  We address this by contrasting streamflow observations with near-natural streamflow simulations. We conclude that while the lack of precipitation dominates streamflow reductions in the megadrought, water uses have not diminished during this time, causing a worsening of the hydrological drought conditions and maladaptation conditions.