Abstract

<strong class="journal-contentHeaderColor">Abstract.</strong> On 12 and 13 September 2019, a long-lasting heavy precipitation episode (HPE) affected the València, Murcia and Almería regions in eastern Spain. Observed rainfall amounts were close to 500 mm in 48 h, being the highest cumulative precipitation registered in some rain gauges for the last century. Subsequent widespread flash flooding caused seven fatalities and estimated economical losses above EUR 425 million. High-resolution precipitation estimates from weather radar observations and flood response from stream gauges are used in combination with a fully distributed hydrological model to examine the main hydrometeorological processes within the HyMeX programme. This HPE was characterized by successive, well-organized convective structures that impacted a spatial extent of 7500 km<span class="inline-formula"><sup>2</sup></span>, with rainfall amounts equal to or larger than 200 mm. The main factors driving the flood response were quasi-stationarity of heavy precipitation, very dry initial soil moisture conditions and large storage capacities. Most of the examined catchments exhibited a dampened and delayed hydrological response to cumulative precipitation: until runoff thresholds were exceeded, infiltration-excess runoff generation did not start. This threshold-based hydrological behaviour may impact the shape of flood peak distributions, hindering strict flood frequency statistical analysis due to the generally limited lengths of data records in arid and semi-arid catchments. As an alternative, a power-law relationship is analytically derived to specifically link flood magnitude to rainfall amount, with the parameters depending on basin and precipitation features. This power law could aid in developing empirical envelope curves so as to assess hydrologic risk in arid and semi-arid catchments with a threshold-based hydrological behaviour.

Highlights

  • Flash floods are among the most devastating natural hazards in terms of economic losses and death toll worldwide (e.g., CRED 2016; Petrucci et al 2019)

  • The heavy precipitation episode (HPE) was divided into three stages from an evaluation of the different convective structures: phase 1 consisted of a quasistationary and elongated area of anchored convection, resulting in long-lasting precipitation over the northernmost watershed; phase 2 was the result of a linear convective system impacting the central and southern basins, and; in phase 3, the formation and subsequent evolution of a V-shaped mesoscale convective system (MCS) overwhelmed the central catchments, while intense convective band activity 470 was affecting the southernmost basin

  • The strong role of the initial conditions was another noticeable characteristic of the 12-13 September 2019 hydrometeorological episode: Runoff coefficients ranged 480 between 0.04–0.16 over the flashiest basins, resulting in highly nonlinear hydrological responses

Read more

Summary

Introduction

Flash floods are among the most devastating natural hazards in terms of economic losses and death toll worldwide (e.g., CRED 2016; Petrucci et al 2019). Some authors have pointed out that rainfall-runoff processes governing flash floods in arid and semi-arid basins such as, convectively-driven precipitation, infiltration-excess runoff and surface water movement in hillslopes and channels, are highly variable in space and time, the aggregated behaviour of peak flows exhibits certain scale invariances with the parameters. 1996 and 2000; Ogden et al 2000; Gaume et al 2003 and 2004; Delrieu et al 2005; Borga et al 2007, Zanon et al 2010), the first objective is to examine the main rainfall and runoff processes that concurred in the unfolding of this extreme episode At this aim, highresolution quantitative precipitation estimates (QPEs) derived from weather radar observations and flood measurements from 90 automatic stream-gauges are used together with a fully-distributed hydrological model. Both objectives are framed within the main scientific goals of the heavy rainfall, flash floods and floods section of HyMeX

Selected catchments: an overview 100
Quantitative precipitation estimates
Precipitation analyses
Flood response and catchment dynamics
Hydrological modelling
Model performance and water balance
Scale dependency between flood magnitude and rainfall amount
Numerical exploration The 12-13
Conclusions and further remarks
Findings
505 Acknowledgements
Full Text
Published version (Free)

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call