Effect of GPR-derived within-field soil moisture variability on the runoff response using a distributed hydrologic model

Abstract

Abstract. The importance of the spatial variability of the antecedent soil moisture conditions on the runoff response is widely acknowledged in hillslope hydrology. Using a distributed hydrologic model, this paper aims at investigating the effects of soil moisture spatial variability on the runoff in various field conditions and at finding the soil moisture scenario that behaves the most closely as the measured soil moisture pattern in term of runoff hydrograph. Soil moisture was surveyed in ten different field campaigns using a proximal ground penetrating radar (GPR) that allowed to perform high-resolution (~m) mapping at the field scale (several ha). Based on these soil moisture measurements, seven scenarios of antecedent soil moisture were used to feed hydrological simulations and the resulting hydrographs were compared. The novelty of this work is to benefit from high-resolution soil moisture measurements using an advanced GPR in various soil moisture conditions. Accounting for the spatial variability of soil moisture resulted in a larger discharge than using a spatially constant soil moisture. The ranges of possible hydrographs were delineated by the extreme scenarios where soil moisture was directly and inversely arranged according to the topographic wetness index (TWI). These behaviours could be explained in terms of runoff contributing areas, with respect to their sizes and their relative locations within the field. The most efficient scenario for soil moisture appeared to be when soil moisture is directly arranged according to the TWI. This was related to the correlation of the measured soil moisture and the TWI. These observations generalised some of the statements pointed out in previous studies. Similar findings are thus expected under similar soil and rainfall forcing conditions.