Experimentation and modeling of soil evaporation in underground dam in a semiarid region

ABSTRACT In semi-arid regions, there is a high evaporation, which leads to soil dryness, interfering in the availability of water in the soil. Usually it is difficult to measure and model the evaporation due to the complexity of the available methods, the low soil water content and the low concentration of water vapor in the air. This can also make it difficult to monitor and simulate the evapotranspiration in these regions. Thus, the Portable Chamber method is used to directly measure evaporation and evapotranspiration, because this technique allows real time estimation and in short time intervals, giving a more detailed estimation of those processes. The objective of this study was to evaluate the evaporation through the mass transfer in the soil in an underground dam under different water table depths and conditions of the semi-arid environment of Pernambuco State in Brazil, through the values predicted by the SiSPAT model and measured by the portable chamber method. For the purposing of modeling and also to better know the soil behavior, soil hydraulic properties were determined though the Beerkan method. The portable chamber method was applied for one of the first times in a semi-arid region of Northeastern Brazil, and it was consistent with the potential evaporation of bare soil, reaching about 1,800 mm per year. The SiSPAT model was quite satisfactory for simulation of soil evaporation in different conditions of the water table depth. The values found for soil evaporation with the simulation of the SiSPAT and the Portable Chamber (PC) method differed in 1.43% and 4.44% for cases where the water table was at 0.20 and 1.20m of depth, respectively.

摘要 半干旱地区蒸发量居高不下，易引发土壤干旱，进而干扰土壤水分有效性。受现有测定方法复杂、土壤含水量偏低及空气中水汽浓度较低等因素影响，常规蒸发量的测量与模拟难度较大，也使得这类区域的蒸发蒸腾监测与模拟工作面临诸多挑战。为此，本研究采用便携式箱法（Portable Chamber）直接测定蒸发与蒸发蒸腾量，该技术可实现实时估算且时间间隔较短，能更细致地解析相关过程。本研究旨在基于SiSPAT模型（SiSPAT）的预测值与便携式箱法的实测值，评估巴西伯南布哥州半干旱环境下不同地下水位深度条件下地下坝区域的土壤传质蒸发量；同时为构建模型并深入解析土壤特性，通过Beerkan法（Beerkan）测定了土壤水力参数。本次研究是便携式箱法在巴西东北部半干旱地区的首批应用案例之一，其测定结果与裸土潜在蒸发量相符，年蒸发量可达约1800 mm。SiSPAT模型在不同地下水位深度条件下的土壤蒸发模拟效果较为理想：当地下水位分别为0.20 m和1.20 m时，SiSPAT模拟的土壤蒸发值与便携式箱法（PC）测定值的相对偏差分别为1.43%和4.44%。