Preprints
https://doi.org/10.5194/hess-2021-230
https://doi.org/10.5194/hess-2021-230

  27 Apr 2021

27 Apr 2021

Review status: this preprint is currently under review for the journal HESS.

Evapotranspiration enhancement drives the European water-budget deficit during multi-year droughts

Christian Massari1, Francesco Avanzi2, Giulia Bruno2,4, Simone Gabellani2, Daniele Penna3, and Stefania Camici1 Christian Massari et al.
  • 1National Research Council (CNR), Research Institute for Geo-Hydrological Protection, Perugia, 06126, Italy
  • 2Cima Research Foundation, 17100, Savona, Italy
  • 3University of Florence, Firenze, Italy
  • 4University of Genoa, DIBRIS, 16145, Genova, Italy

Abstract. In a warming climate, periods with below-than-average precipitation will increase in frequency and intensity. During such periods, known as meteorological droughts, sparse but consistent pieces of evidence show that the decline in annual runoff may be proportionally larger than the corresponding decline in precipitation (e.g., −40 % vs. −20 %). Reasons behind this exacerbation of runoff deficit during dry periods remain largely unknown, which challenges generalization at larger scales (i.e., beyond the single catchment), as well as the predictability of when this exacerbation will occur and how intense it will be. Here, we tested the hypothesis that runoff-deficit exacerbation during droughts is a common feature of droughts across climates and is driven by evapotranspiration enhancement. We support this hypothesis by relying on multidecadal records of streamflow and precipitation for more than 200 catchments across various European climates, which distinctively show the emergence of similar periods of exacerbated runoff deficit identified in previous studies, i.e., runoff deficit on the order of −20 % to −40 % less than what expected from precipitation deficit. The magnitude of this exacerbation is two to three times larger for basins located in dry regions than for basins in wet regions and is qualitatively correlated with an increase in annual evapotranspiration during droughts, on the order of 11 % and 33 % over basins characterized by energy- and water-limited evapotranspiration regimes, respectively. Thus, enhanced atmospheric and vegetation demand for moisture during dry periods induces a nonlinear and potentially hysteretic precipitation-runoff relationship for low-flow regimes, which results in an unexpectedly large decrease in runoff during periods of already low water availability. Forecasting onset, magnitude, and duration of these drops in runoff availability has paramount societal implications, especially in a warming climate, given their supporting role for water, food, and energy security. The outcome that water basins are prone to this exacerbation of runoff deficit for various climates and evapotranspiration regimes, compounded by the lack of specific parametrizations of this process in the majority of hydrological and land-surface models, make further understanding of its patterns of predictability an urgent priority for water-resource planning and management in a warming and drier climate.

Christian Massari et al.

Status: open (extended)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on hess-2021-230', Anonymous Referee #1, 07 Jun 2021 reply
    • AC1: 'Reply on RC1', Christian Massari, 17 Jun 2021 reply

Christian Massari et al.

Christian Massari et al.

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Short summary
Water withdrawal from rivers accounts for approximately 25 % of the global continental runoff and is vital for sustaining population water demands. Here, we show that runoff-deficit during droughts is much less than expected based on the observed decline in precipitation and is driven by evapotranspiration enhancement which shows an increase up to 30 % in median over dry climates. These findings have paramount societal implications, for water, food, and energy security.