Preprints
https://doi.org/10.5194/hess-2021-352
https://doi.org/10.5194/hess-2021-352

  13 Jul 2021

13 Jul 2021

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

Rainfall-runoff relationships at event scale in western Mediterranean ephemeral streams

Roberto Serrano-Notivoli1, Alberto Martínez-Salvador2, Rafael García-Lorenzo2, David Espín-Sánchez2, and Carmelo Conesa-García2 Roberto Serrano-Notivoli et al.
  • 1Department of Geography, Autonomous University of Madrid, Madrid, 28049, Spain
  • 2Department of Geography, University of Murcia, Murcia, 30001, Spain

Abstract. Ephemeral streams are highly dependent on rainfall and terrain characteristics and, therefore, very sensitive to minor changes in these environments. Western Mediterranean area exhibits a highly irregular precipitation regime with a great variety of rainfall events driving the flow generation on intermittent watercourses, and future climate change scenarios depict a lower magnitude and higher intensity of precipitation in this area, potentially leading to severe changes in flows. We explored the rainfall-runoff relationships in two semiarid watersheds in southern Spain (Algeciras and Upper Mula) to model the different types of rainfall events required to generate new flow in both intermittent streams. We used a nonlinear approach through Generalized Additive Models at event scale in terms of magnitude, duration, and intensity, contextualizing resulting thresholds in a long-term perspective through the calculation of return periods. Results showed that the average ~ 1.2-day and <1.5 mm event was not enough to create new flows. At least a 4-day event ranging from 4 to 20 mm, depending on the watershed was needed to ensure new flow at a high probability (95 %). While these thresholds represented low return periods (from 4 to 10 years), the great irregularity of annual precipitation and rainfall characteristics, makes prediction highly uncertain. Almost a third part of the rainfall events resulted in similar or lower flow than previous day, emphasizing the importance of lithological and terrain characteristics that lead to differences in flow generation between the watersheds.

Roberto Serrano-Notivoli et al.

Status: open (until 07 Sep 2021)

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Roberto Serrano-Notivoli et al.

Roberto Serrano-Notivoli et al.

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Short summary
Ephemeral streams in western Mediterranean area are driven by the duration, magnitude, and intensity of the rainfall events (RE). A detailed statistical analysis showed that the average RE (1.2 days and 1.5 mm) is not enough to generate new flow, which is only guaranteed by events occurring in return periods from 4 to 10 years. RE explain near to 75 % of new flow, meaning that terrain and lithological characteristics play a fundamental role.