A vulnerability assessment method to evaluate the impact of tunnel drainage on terrestrial vegetation under various atmospheric and climatic conditions

Abstract

Abstract The impact of tunnel drainage on local water resources has attracted increasing attention in the past decades. The potential impacts of tunnel drainage on terrestrial vegetation have been evaluated from a groundwater environment perspective. However, previous attempts did not consider the atmospheric and climatic conditions along with the change to the regional groundwater table. To address the lack of atmospheric influence, this study proposes a vulnerability assessment method focused on the soil-plant-atmosphere continuum by taking tunnel drainage, atmospheric and climatic impacts into account. The proposed method consists of five stages: (1) groundwater seepage model for water table distribution, (2) topsoil model based on a single column perspective for soil water pressure distributions, (3) dynamic root-zone wilting for the transient model, (4) Budyko-type analysis for the soil water storage under longer-term climatic changes, and (5) summary based on the outcomes of vulnerability analysis. The case study was located in the Yuexi county (Anhui, East China) and was investigated based on different soil textures, weather conditions, and groundwater table drawdown scenarios. Transient intra-annual water pressure dynamics were simulated for one year, and aggregate variations of soil water storage were summarized using the Budyko framework. The assessment method demonstrated that the textural differences and climatic changes are more impactful on plant vulnerability compared to the drainage effect in the specific case. The increase in aridity towards the sub-humid dry climate drives the soil columns to decrease the water storage, where the significant loss of water storage was also observed in the Budyko-type framework. The outcomes suggest that under sub-humid dry conditions when combined with tunnel drainage, the drawdown on shallow groundwater levels leads the vegetation to be vulnerable.