Calibración de Sensores de Humedad del Suelo y Determinación de Firmas Hidrológicas : Calibración Sensor de Humedad de Suelo y Firmas Hidrológicas “C02”.

Abstract

Soil moisture influences water cycle processes in the interactions between the land surface and the atmosphere. In Quito, the Empresa Pública Metropolitana de Agua Potable y Saneamiento de Quito (EPMAPS) ensures water availability and issues alerts for heavy rainfall through its hydrometeorological network. This network includes the Rumihurco station (C02). At station C02, the volumetric water content (θv) is determined using the time domain reflectometry (TDR) method, where permittivity (Ka) data are used with Topp's equation to obtain soil moisture data. However, the predetermined equation tends to underestimate the data in some soils, as specified in the Campbell manual for the CS650 sensor used at the Rumihurco station. Therefore, a specific calibration equation must be obtained for station C02. Calibrated θv data allows for the determination of a time series that presents the relationship between precipitation and soil moisture over a given time period. Additionally, calibrated data provides a hydrological signature through a probability density function (PDF) that allows for a detailed and qualitative presentation of the variability of θv in the soil. The calibration curve is obtained from an undisturbed sample within a PVC cylinder with a diameter of 40 cm and a height of 30 cm. In the laboratory, samples are taken to obtain the calibration curve and also to characterize the soil by determining pH, electrical conductivity, organic matter content, carbon content, porosity, and bulk density. Laboratory analyses determined that the soil at the Rumihurco station is silty sand, with 6.37 pH, electrical conductivity of 6.37 µS/cm, 5.91% organic matter, 3.42% organic carbon, 66% porosity, and a bulk density of 1.008 g/cm³. Upon completing the calibration curve, it was determined that Topp's equation underestimates the (θv) values, because the values obtained with the specific calibration equation show slightly higher soil moisture values and correlate with the time series, indicating that higher precipitation increases the volumetric water content in the soil. Furthermore, the obtained PDF demonstrates that there are three predominant peaks regarding the probability of obtaining θv, through a multimodal distribution.