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

Roberto Serrano-Notivoli,David Espín-Sánchez,Alberto Martínez-Salvador,Rafael García-Lorenzo,Carmelo Conesa-García

doi:10.5194/hess-26-1243-2022

Roberto Serrano-Notivoli, David Espín-Sánchez + Show 3 more

Open Access

https://doi.org/10.5194/hess-26-1243-2022

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Abstract

Abstract. Ephemeral streams are highly dependent on rainfall and terrain characteristics and, therefore, very sensitive to minor changes in these environments. The 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 semi-arid 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 non-linear 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 d and < 1.5 mm event was not enough to create new flows. At least a 4 d 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, the great irregularity of annual precipitation and rainfall characteristics makes prediction highly uncertain. Almost a third of the rainfall events resulted in similar flow to or lower flow than the previous day, emphasizing the importance of lithological and terrain characteristics that lead to differences in flow generation between the watersheds.

Highlights

Precipitation plays a paramount role in the drainage of watersheds, especially in those depending on rainfall for the persistence of the flows, considered intermittent streams
Average daily flows (Q) in Algeciras and Mula were relatively low in both watersheds (0.29 and 0.15 m3 s−1, respectively) and these values were distant from the median of each month (Fig. 3), denoting their great irregularity
Terrain characteristics play a key role in rainfall–runoff relationships and in the amount of Q per month

Summary

Introduction

Precipitation plays a paramount role in the drainage of watersheds, especially in those depending on rainfall for the persistence of the flows, considered intermittent streams. These types of watercourses, occasionally dry, are already a largescale phenomenon (Acuña et al, 2005; Larned et al, 2010; Datry et al, 2014) and could be potentially increased under climate change conditions (Nabih et al, 2021; Brunner et al, 2020; Skoulikidis et al, 2017; Brooks, 2009). The western Mediterranean area is especially prone to accommodating watersheds with these types of streams because of the high irregularity of precipitation, both in space and time (Tockner et al, 2009; Datry et al, 2017) In ephemeral streams, this irregularity turns into a great uncertainty in flow generation, affecting the stream, and other parts of the system. The fickleness of flows alters the actual ecological functioning of the watershed at variable scales and, affects the agricultural systems covering lowlands that usually require infrastructures to re-

Results

Discussion

Conclusion