A new drought index fitted to clay shrinkage induced subsidence over France: benefits of interactive leaf area index

Abstract

Abstract. Clay shrinkage, which consists of a reduction in the volume of clay soils during dry periods, can affect buildings and cause subsidence damage. In France, losses due to subsidence are estimated at more than 16 billion € for the period 1989–2021 (CCR, 2021), and are expected to increase under the effect of climate warming. This work aims to improve the current understanding of the conditions triggering subsidence by proposing an innovative drought index. We use a daily Soil Wetness Index (SWI) to develop a new annual drought index that can be related to subsidence damage. The SWI is derived from simulations of soil moisture profiles from the Interactions between Soil, Biosphere, Atmosphere (ISBA) land surface model developed by Météo-France. The ability of the drought index to correlate with insurance claims data is assessed by calculating the Kendall rank correlation over twenty municipalities in France. The insurance data, aggregated by year and municipality, are provided by the Caisse Centrale de Réassurance (CCR). A total of 1200 configurations of the drought index are considered. They are generated by combining different calculation methods, ISBA simulation settings, soil model layers, and drought percentile thresholds. The analysis includes a comparison with the independent claim data of six additional municipalities, and to a record of official “CatNat” decrees, useful for the analysis. The best results are obtained for drought magnitudes based on SWI values of the 0.8 m to 1.0 m deep soil layer, an ISBA simulation with interactive leaf area index (LAI), and consideration of low drought SWI percentile thresholds. Comparison with claim data shows that drought magnitude is able to identify subsidence events while being spatially consistent. This drought magnitude index provides more insight into subsidence triggers while benefiting from advanced land surface modeling schemes (interactive LAI, multi-layer soil). This work paves the way for more reliable damage estimates.

A new approach for drought index adjustment to clay-shrinkage-induced subsidence over France: advantages of the interactive leaf area index

“…Data availability. The data presented in the figures are available online at https://doi.org/10.6084/m9.figshare.23559507 (Barthelemy, 2023). Geographic distribution of exposed single-family houses can be downloaded freely at https://www.statistiques.developpement-durable.gouv.fr/nouveauzonage-dexposition-au-retrait-gonflement-des-argiles-plus-de-104millions-de-maisons (MTES, 2021b).…”

Unveiling the Hidden Threat: Drought‐Induced Inelastic Subsidence in Expansive Soils

“…Elastic deformation often retains large amplitudes and has immediate impacts on structures and infrastructure. There are significant studies about the elastic deformation of expansive soils under varying moisture conditions in geotechnical engineering, often referred as seasonal subsidence and heave (e.g., Barthélémy et al., 2023; Charpentier et al., 2022; Kai et al., 2020; Mostafiz et al., 2021; Wang, 2022a). These studies have been pivotal in understanding soil behavior under drought conditions and their corresponding damage to buildings and infrastructures.…”