Abstract
Abstract. The role and the importance of soil moisture for meteorological, agricultural and hydrological applications is widely known. Remote sensing offers the unique capability to monitor soil moisture over large areas (catchment scale) with, nowadays, a temporal resolution suitable for hydrological purposes. However, the accuracy of the remotely sensed soil moisture estimates has to be carefully checked. The validation of these estimates with in-situ measurements is not straightforward due the well-known problems related to the spatial mismatch and the measurement accuracy. The analysis of the effects deriving from assimilating remotely sensed soil moisture data into hydrological or meteorological models could represent a more valuable method to test their reliability. In particular, the assimilation of satellite-derived soil moisture estimates into rainfall-runoff models at different scales and over different regions represents an important scientific and operational issue. In this study, the soil wetness index (SWI) product derived from the Advanced SCATterometer (ASCAT) sensor onboard of the Metop satellite was tested. The SWI was firstly compared with the soil moisture temporal pattern derived from a continuous rainfall-runoff model (MISDc) to assess its relationship with modeled data. Then, by using a simple data assimilation technique, the linearly rescaled SWI that matches the range of variability of modelled data (denoted as SWI*) was assimilated into MISDc and the model performance on flood estimation was analyzed. Moreover, three synthetic experiments considering errors on rainfall, model parameters and initial soil wetness conditions were carried out. These experiments allowed to further investigate the SWI potential when uncertain conditions take place. The most significant flood events, which occurred in the period 2000–2009 on five subcatchments of the Upper Tiber River in central Italy, ranging in extension between 100 and 650 km2, were used as case studies. Results reveal that the SWI derived from the ASCAT sensor can be conveniently adopted to improve runoff prediction in the study area, mainly if the initial soil wetness conditions are unknown.
Highlights
Soil moisture plays a fundamental role in the partitioning of rainfall into runoff and infiltration inside a catchment
In the soil water balance (SWB) model the processes are represented for infiltration through the Green-Ampt equation, for percolation by a gravity driven non-linear relationship and for actual evapotranspiration considering a linear relationship with the potential one, based on a modified Blaney and Criddle approach
SWI, the soil wetness index derived from Advanced Scatterometer (ASCAT), was found strongly correlated with the simulated saturation degree, with determination coefficients (R2) higher than 0.90 and RMSE values less than 0.014 m3/m3
Summary
Soil moisture plays a fundamental role in the partitioning of rainfall into runoff and infiltration inside a catchment. For a given storm event, different values of initial soil moisture conditions can discriminate between minor or catastrophic flooding effects Crow et al, 2005; Brocca et al, 2008; Berthet et al, 2009; Merz and Bloschl, 2009). The assimilation of soil moisture information within rainfall-runoff models can provide, in theory, a great improvement for both runoff prediction and forecasting. Several studies investigated the use of soil moisture observations within rainfall-runoff models by using, basically, three different methodologies.
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