Assessment of water dynamics in an unsaturated soil under simulated rainfall conditions

Abstract

The Brazilian semi-arid region presents soils with small thickness and low permeability, where the precipitated water remains in the superficial layer of the soil and quickly evaporates. Although this condition leads to a shallow water table, it plays a key role during drought periods, especially for the native vegetation of the semi-arid Caatinga. The main objective of this work is to estimate the effect of rainfall intensity on soil water dynamics in a semi - arid region of the state of Pernambuco, Brazil. One-dimensional mathematical modeling of soil water dynamics using 1D-Hydrus software was performed. Four different precipitation rates and duration times of rainfall events were used, based on values measured in loco. Most precipitous rains were contained in the first 15 centimeters of the soil. The results indicated that the intense rainfall events of shorter duration determine higher values in the soil surface moisture. Less intense and longer duration events lead to an increase in soil moisture content for a longer period of time, approximately for 3 days, regardless of precipitation intensity. Rainfall events increase soil surface volumetric moisture rapidly, but when they cease, volumetric moisture returns to baseline slowly, about 10 days after rainy events.