1 research outputs found
How does initial soil moisture influence the hydrological response? A case study from southern France
The Cévennes–Vivarais region in southern France is prone to heavy rainfall
that can lead to flash floods which are one of the most hazardous natural
risks in Europe. The results of numerous studies show that besides rainfall
and physical catchment characteristics the catchment's initial soil moisture
also impacts the hydrological response to rain events. The aim of this paper
is to analyze the relationship between catchment mean initial soil moisture
θ̃ini and the hydrological response that is
quantified using the event-based runoff coefficient Ï•ev in
the two nested catchments of the Gazel (3.4 km2) and the Claduègne
(43 km2). Thus, the objectives are twofold: (1)Â obtaining meaningful
estimates of soil moisture at catchment scale from a dense network of in situ
measurements and (2) using this estimate of θ̃ini
to analyze its relation with Ï•ev calculated for many runoff
events. A sampling setup including 45Â permanently installed frequency domain
reflectancy probes that continuously measure soil moisture at three depths is
applied. Additionally, on-alert surface measurements at ≈10 locations in each one of 11 plots are conducted. Thus, catchment mean
soil moisture can be confidently assessed with a standard error of the mean
of ≤1.7 vol % over a wide range of soil moisture conditions.
The Ï•ev is calculated from high-resolution discharge and
precipitation data for several rain events with a cumulative precipitation
Pcum ranging from less than 5 mm to more than 80 mm. Because of the high
uncertainty of Ï•ev associated with the hydrograph separation
method, Ï•ev is calculated with several methods, including
graphical methods, digital filters and a tracer-based method. The results
indicate that the hydrological response depends on θ̃ini: during dry conditions ϕev is consistently
below 0.1, even for events with high and intense precipitation. Above a
threshold of θ̃ini=34 vol % Ï•ev can reach values up to 0.99 but there is a high scatter. Some
variability can be explained with a weak correlation of Ï•ev with
Pcum and rain intensity, but a considerable part of the variability
remains unexplained.
It is concluded that threshold-based methods can be helpful to prevent
overestimation of the hydrological response during dry catchment conditions.
The impact of soil moisture on the hydrological response during wet
catchment conditions, however, is still insufficiently understood and cannot
be generalized based on the present results.</p