Multilevel and multiscale drought reanalysis over France with the Safran-Isba-Modcou hydrometeorological suite

Abstract

Abstract.Physically-based droughts can be defined as a water deficit in at least one component of the land surface hydrological cycle. The reliance of different activity domains (water supply, irrigation, hydropower, etc.) on specific components of this cycle requires drought monitoring to be based on indices related to meteorological, agricultural, and hydrological droughts. This paper describes a high-resolution retrospective analysis of such droughts in France over the last fifty years, based on the Safran-Isba-Modcou (SIM) hydrometeorological suite. The high-resolution 1958-2008 Safran atmospheric reanalysis was used to force the Isba land surface scheme and the hydrogeological model Modcou. Meteorological droughts are characterized with the Standardized Precipitation Index (SPI) at time scales varying from 1 to 24 months. Similar standardizing methods were applied to soil moisture and streamflow for identifying multiscale agricultural droughts -through the Standardized Soil Wetness Index (SSWI) -and multiscale hydrological droughts, through the Standardized Flow Index (SFI). Based on a common threshold level for all indices, drought event statistics over the 50-yr period -number of events, duration, severity and magnitude -have been derived locally in order to highlight regional differences at multiple time scales and at multiple levels of the hydrological cycle (precipitation, soil moisture, streamflow). Results show a substantial variety of temporal drought patterns over the country that are highly dependent on both the variable and time scale considered. Independent spatio-temporal drought events have then been identified and described by combining local characteristics with the evolution of area under drought. Summary statistics Correspondence to: J.-P. Vidal (jean-philippe.vidal@cemagref.fr) have finally been used to compare past severe drought events, from multi-year precipitation deficits (1989)(1990)) to short hot and dry periods (2003). Results show that the ranking of drought events depends highly on both the time scale and the variable considered. This multilevel and multiscale drought climatology will serve as a basis for assessing the impacts of climate change on droughts in France.

Multiscale evaluation of the Standardized Precipitation Index as a groundwater drought indicator

“…The resulting quantiles, bounded on [0, 1], are denoted hereafter as the SPI and SGI for precipitation and groundwater, respectively. The quantile-based index has been used in several recent drought studies (Sheffield et al, 2004;Andreadis et al, 2005;Vidal et al, 2010;Samaniego et al, 2013), and can be easily transformed to the unbounded range of the standard normal distribution (Vidal et al, 2010). The SPI and SGI values below (above) 0.5 denote dry (wet) conditions.…”

“…A non-parametric approach was used here to avoid the problem of assigning a unique distribution function to all data sets (as mentioned above), and to ensure the consistency in the estimation of drought indices for the precipitation and groundwater time series (i.e., both variables use a similar approach so that the resulting drought indices fall within the same range [0, 1]). We note that many recent drought studies have adopted a non-parameteric approach for the estimation of drought indices (see, e.g., Andreadis et al, 2005;Vidal et al, 2010;Bloomfield and Marchant, 2013;Samaniego et al, 2013;Hao et al, 2014). Bloomfield and Marchant (2013), for example, had difficulties in identifying a unique best distribution function that fits all groundwater records at various locations, and even at a given location a fitted distribution function varied from one calendar month to another.…”

“…Another approach to quantifying drought is based on the use of large-scale gridded data products, e.g., from hydrologic models or satellites (e.g., Sheffield et al, 2004;Andreadis et al, 2005;Vidal et al, 2010;Samaniego et al, 2013;van Huijgevoort et al, 2013;Prudhomme et al, 2014;Mo and Lettenmaier, 2013;Nijssen et al, 2014;Hao et al, 2014;Li and Rodell, 2015;Damberg and AghaKouchak, 2014;Wanders et al, 2015;AghaKouchak et al, 2015). An extensive multi-model study (Prudhomme et al, 2014), for example, projected increases in hydrological drought severity in many areas around the world.…”

Spatiotemporal dynamics of global drought

“…However, the regional scale of these studies still bounds the frame of analysis and prevents a thorough comparison of the spatio-temporal characteristics of drought across the globe. Furthermore, previous studies have been limited to simple assessments of the time series of drought area and intensity [Vicente-Serrano, 2006;Vidal et al, 2010;Gocic et al, 2014;Wang et al, 2015], report aggregate regional drought statistics that do not provide insight into the behavior of individual events [Tallaksen and Stahl, 2014;Ge et al, 2016].…”

“…Some studies at the country [e.g. Vicente-Serrano, 2006;Vidal et al, 2010;Xu et al, 2015;Zhai et al 2016] and continental [Lloyd-Hughes, 2012] scales have explored drought cluster characteristics (e.g. distribution of centroids, direction of displacement over time, and changes in cluster area, intensity, and severity).…”