Gilles Molinié

HyMeX-SOP1: The Field Campaign Dedicated to Heavy Precipitation and Flash Flooding in the Northwestern Mediterranean

The Mediterranean region is frequently affected by heavy precipitation events associated with flash floods, landslides, and mudslides that cause hundreds of millions of euros in damages per year and often, casualties. A major field campaign was devoted to heavy precipitation and flash floods from 5 September to 6 November 2012 within the framework of the 10-year international HyMeX (Hydrological cycle in the Mediterranean Experiment) dedicated to the hydrological cycle and related high-impact events. The 2- month field campaign took place over the Northwestern Mediterranean Sea and its surrounding coastal regions in France, Italy, and Spain. The observation strategy of the field experiment was devised to improve our knowledge on the following key components leading to heavy precipitation and flash flooding in the region: i) the marine atmospheric flows that transport moist and conditionally unstable air towards the coasts; ii) the Mediterranean Sea acting as a moisture and energy source; iii) the dynamics and microphysics of the convective systems producing heavy precipitation; iv) the hydrological processes during flash floods. This article provides the rationale for developing this first HyMeX field experiment and an overview of its design and execution. Highlights of some Intense Observation Periods illustrate the potential of the unique datasets collected for process understanding, model improvement and data assimilation.

Spatial analysis of trend in extreme daily rainfall in southern France

This paper makes a regional evaluation of trend in yearly maxima of daily rainfall in southern France, both at point and spatial scales on a regular grid of 8xa0×xa08xa0km2. In order to filter out the high variability of rainfall maxima, the current analysis is based on a non-stationary GEV modeling in which the location parameter is allowed to vary with time. Three non-stationary models are considered for each series of maxima by constraining the location parameter to vary either linearly, linearly after a given date or linearly up to a final date. Statistical criteria are used to compare these models and select the best starting or final point of putative trends. The analysis shows that, at regional scale, the best distribution of maxima involves a linear trend starting in year 1985 and that this trend is significant in half the region, including most of the mountain ranges and part of the Rhône valley. Increases in yearly maxima are considerable since they reach up more than 60xa0mm/day in 20xa0years, which is more than 40xa0% of the average maximum in this area.

Climatology of observed rainfall in Southeast France at the Regional Climate Model scales

In order to provide convenient data to assess rainfall simulated by Regional Climate Models, a spatial database (hereafter called K-REF) has been designed. This database is used to examine climatological features of rainfall in Southeast France, a study region characterized by two mountain ranges of comparable altitude (the Cévennes and the Alps foothill) on both sides of the Rhône valley. Hourly records from 1993 to 2013 have been interpolated to a

Raindrops size and shape from videosonde and image processing

0.1^{circ } times 0.1^{circ }

A high space–time resolution dataset linking meteorological forcing and hydro-sedimentary response in a mesoscale Mediterranean catchment (Auzon) of the Ardèche region, France

0.1∘×0.1∘ latitude–longitude regular grid and accumulated over 3-h periods in K-REF. The assessment of K-REF relatively to the SAFRAN daily rainfall reanalysis indicates consistent patterns and magnitudes between the two datasets even though K-REF fields are smoother. A multi-scale analysis of the occurrence and non-zero intensity of rainfall is performed and shows that the maps of the 50th and 95th percentiles of 3- and 24-h rain intensity highlight different patterns. The maxima of the 50th and 95th percentiles are located over plain and mountainous areas respectively. Moreover, the location of these maxima is not the same for the 3- and 24-h intensities. To understand these differences between median and intense rainfall on the one hand and between the 3- and 24-h rainfall on the other hand, we analyze the statistical distributions and the space-time structure of occurrence and intensity of the 3-h rainfall in two classes of days, defined as median and intense. This analysis illustrates the influence of two factors on the triggering and the intensity of rain in the region: the solar cycle and the orography. The orographic forcing appears to be quite different for the two ranges of the domain and is much more pronounced over the Cévennes.

How does initial soil moisture influence the hydrological response? Acase study from southern France

This paper describes a videosonde designed for providing shape and size of raindrops. It makes use of a single CCD camera and image processing to detect raindrops, to segment and measure shape and size of each detected particle. Depth is obtained by one fixed camera with 2 lights, which is a key feature of the video sonde. Raindrops are detected by their 2 shadows. As no model are accurate to represent raindrops, image processing uses a-contrario method for detection, and constraint filtering for matching. Results are evaluated on glass ball and real rain simulator.

GT Précipitation (SIRTA)

This paper describes a new videosonde designed for providing shape and size of raindrops. It makes use of a CCD camera and image processing to acquire image sequence, to detect raindrops, to segment and measure shape and size of each detected particle. Depth is obtained by one fixed camera with 2 lights, which is a key feature of the video sonde. Raindrops are detected by their 2 shadows. As no model are accurate to represent raindrops, image processing uses a-contrario method for detection, and constraint filtering for matching. Results are evaluated on glass ball and real rain simulator.