Local influence of south-east France topography and land cover on the distribution and characteristics of intense rainfall cells

Abstract

The Greater Lyon area is strongly built up, grouping 58 communes and a population of 1.3 million in approximately 500 km 2 . The flood risk is high as the territory is crossed by two large watercourses and by streams with torrential flow. Floods may also occur in case of runoff after heavy rain or because of a rise in the groundwater level. The whole territory can therefore be affected, and it is necessary to possess in-depth knowledge of the depths, causes and consequences of rainfall to achieve better management of precipitation in urban areas and to reduce flood risk. This study is thus focused on the effects of topography and land cover on the occurrence, intensity and area of intense rainfall cells. They are identified by local radar meteorology (C-band) combined with a processing algorithm running in a geographic information system (GIS) which identified 109,979 weighted mean centres of them in a sample composed of the five most intense rainfall events from 2001 to 2005. First, analysis of spatial distribution at an overall scale is performed, completed by study at a more detailed scale. The results show that the distribution of high-intensity rainfall cells is spread in cluster form. Subsequently, comparison of intense rainfall cells with the topography shows that cell density is closely linked with land slope but that, above all, urbanised zones feature nearly twice as many rainfall cells as farm land or forest, with more intense intensity.

Meteorological aspects of heavy precipitation in relation to floods – An overview

“…The land surface itself has an important influence on heavy precipitation. According to Funatsu and Waugh (2008) and Renard (2017) local land surface characteristics exert primary control on the existence and strength of convection (i.c. occurrence, intensity and area of rainfall or precipitation cells).…”

“…According to Smith et al (1994a) and Javier Julie Rose et al (2010) heavy precipitation exhibits large spatial and temporal variability. The precipitation (spatiotemporal) variability can be further increased by the storm's propagation mechanism (Smith et al, 1996), the storm's microstructure (Smith et al, 2001) and the irregularity of the topography (Yu et al, 2015) or land slope (Renard, 2017), especially in mountainous areas (Buytaert et al, 2006;Pinto et al, 2013;Yang et al, 2017b) and in urban areas even in a small area (Piotrowski, 2017). In this respect one can consider the altitude, slope and aspect of the topography that influence rain shading and wind speed and so precipitation variability.…”

“…50 mm in an hour) will occur. It becomes clear that a heavy precipitation event can only be expected at certain specific meteorological conditions at which both large-scale, mesoscale and local scale conditions do matter and these conditions can differ greatly with location and time (Renard, 2017;Ricard et al, 2012). Inherent to it is that a heavy precipitation event is coupled to a specific location and time.…”

Satellite or ground-based measurements for production of site specific hourly irradiance data: Which is most accurate and where?

“…The connection between terrain and irradiance appears to be complex and not easily explained with hourly data (Tables 2 and 3). of objects with features of the same magnitude (Anselin, 2010;Renard, 2017). This index enables statistically significant groups with high (HH) and low (LL) error values to be distinguished.…”

Comparison of solar radiation and PV generation variability: system dispersion in the UK

“…The clusters have been proven to be significant with two geostatistical tools: Anselin Local Moran's I [28] and Getis-Ord Gi* [29,30]. These algorithms have previously been used to analyse weather data [31] and site distribution [32]. ).…”