Abstract
Soil-atmosphere interaction has implications in different scientific research contexts and is increasingly investigated through field measurements. This paper reports a detailed description of interaction between shallow soil and atmosphere at two test sites in Oltrepò Pavese area (Northern Italy). The two test sites are in the same climatic area but are characterised by different geological features. In fact, the first objective is to compare the behaviour of two different soils, namely a clayey-sandy silt (CL) and a silty clay (CH), under similar meteorological events. Soil-atmosphere interaction is studied on the basis of long-term (about 87 and 42 months for the two test sites, respectively) monitoring data of both volumetric water content and soil water potential, recorded at different depths along two vertical soil profiles in the first two metres from ground level. Field measurements, together with meteorological data such as precipitation and air temperature, allow for clear identification of the seasonal fluctuations of unsaturated soil hydraulic properties. To infer detailed information, the recorded data were processed and relationships between soil water potential and water content were investigated. Different time spans, from several months to a few days, even including single rainy events, are considered to show the hydraulic soil behaviour. The hysteretic cycles of water content with respect to soil water potential and non-equilibrium flow are highlighted. In particular, the measured soil water potential is in the range of 0–800 kPa and of 0–1500 kPa for the CL and CH soil, respectively. At both sites, the observed hysteretic cycles are more frequent in the hot season (summer) than in the cold season (winter) and tend to reduce with depth. The experimental results are compared with the soil water characteristic curves (SWCCs) to assess whether and to what extent the SWCCs are reliable in modelling the hydraulic behaviour of partially saturated soils, under atmospheric forcing, at least in the considered climatic contexts.
Highlights
Rainfall infiltration and water redistribution in unsaturated soils as well as the response of shallow soil to atmospheric forcing are natural phenomena that affect different aspects related to the fields of hydrology, geology, ecology and agronomy
London Clay cutting near Newbury (UK); Papa et al (2013) and Pirone et al (2015a, 2015b) acquired seasonal field data in an unsaturated pyroclastic slope at Monteforte Irpino test site; Comegna et al (2016a, b) and Marino et al (2020) reported soil-atmosphere monitoring data collected in a shallow deposits in unsaturated pyroclastic soils covering a steep slope located in Cervinara, southern Italy, where in 1999 a rainfall-induced flowslide occurred; Springman et al (2013) reported results of a long-term field study related to water content and suction fluctuations in Quaternary soil deposits on a grass-covered slope in north Switzerland; Bittelli et al (2012) studied seasonal variations of soil–water conditions leading to landslide occurrence in a high plasticity inorganic clay in the Centonara catchment
Unlike in the shallowest layers, at a depth of 1.2 m only two phases can be observed in the summer period (Fig. 14a): the first is a drying phase covering a soil water potential range of more than 850 joules per kilogram (J/kg), which starts on 15 May 2014 and continues until 31 July, when the wetting path begins after the precipitations of 15.3 mm and 29.7 mm occurred on 24 July and 26 July, respectively
Summary
Rainfall infiltration and water redistribution in unsaturated soils as well as the response of shallow soil to atmospheric forcing are natural phenomena that affect different aspects related to the fields of hydrology, geology, ecology and agronomy. In all the investigated levels at Montuè test site, in less than 1 month without significant cumulated rainfall, water content and soil water potential came back to the values reached before the previous re-wetting.
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