黄土区苹果园土壤剖面水、汽通量模拟研究

Simulation of Water and Vapor Fluxes in Soil Profile of Apple Orchard in Loess Area

黄土疏松多孔且黄土区干旱少雨,汽态水可能在剖面水分运移中扮演重要角色。因此,了解非饱和带土壤水汽通量的循环运移规律,对实现干旱区水资源的可持续发展具有重要意义。基于黄土高原旱地苹果园剖面(0~200 cm)高频定位监测试验,采用水-汽-热-气耦合的STEMMUS(Simultaneous Transfer of Energy,Mass and Momentum in Unsaturated Soil)模型,探讨黄土剖面液态水和汽态水通量运移规律。结果表明:STEMMUS模型准确地再现了旱地苹果园剖面土壤水分(d介于0.81~0.98,NRMSE介于5.5%~15%)和土壤温度(d介于0.98~0.99,NRMSE介于1.4%~4.6%)的动态变化,对苹果树蒸发蒸腾量的模拟表现出良好的一致性(d介于0.92~0.96)。降雨对基质势梯度、温度梯度、液态水与汽态水通量均有显著影响,液态水与汽态水运移分别主要由基质势梯度与温度梯度驱动,且二者对土壤水分的最大补给深度在研究期内分别为100 cm和160 cm,表明土壤水通过向下的汽态水能够运移至更深层土壤。研究结果可增进对黄土剖面水分运移规律的认识。

【Objective】The loess area is arid with little rain and the soil is loose and porous.The water vapor in this area may play an important role in profiling water migration.Thus,it is important to study and understand the cyclic migration law of soil water vapor flux in unsaturated zone for realizing the sustainable development of water resources in arid regions.【Method】To explore the flux transfer rule of liquid water and steam water in loess profile,based on the high-frequency in-situ monitoring test of dryland apple orchard profile(0-200 cm)in Loess area,the simulation of water-vapour-heat-air coupling STEMMUS(Simultaneous Transfer of Energy,Mass and Momentum in Unsaturated Soil)model was adopted in this study.【Result】Results show:(1)STEMMUS model reliably reproduced the dynamic changes of soil moisture(d was between 0.81 and 0.98,NRMSE was between 5.5%and 15%)and soil temperature(d was between 0.98 and 0.99,NRMSE was 1.4%and 4.6%)in the profile of dryland apple orchard.This showed good agreement with the simulation of apple tree evapotranspiration(d was between 0.92 and 0.96).(2)Rainfall had significant effects on matrix potential gradient,temperature gradient,liquid water and water vapor flux.The transport of liquid water and vapor water was mainly driven by the matrix potential gradient and temperature gradient,respectively.During the study period,the maximum recharge depths of the soil moisture was 100 cm and 160 cm,respectively,which indicates that soil water could migrate to deeper soil through downward vapor water.【Conclusion】STEMMUS model considering soil spatial heterogeneity significantly improves the simulation accuracy and reveals the migration law of water vapor flux in loess profile.The research results can deepen the understanding of water migration in the loess profile.