Joint effects of groundwater and aridity index on the transpiration of vegetation:A case study in the Yushen mining area

Hydrus-1D software was used to simulate the joint influences of groundwater and aridity index on the tran- spiration of Salix psammophila based on field investigation,laboratory test and in-situ test. The results showed that the transpiration receives joint influence from the groundwater and aridity index. The transpiration is mainly controlled by groundwater when the water table depth is 1. 0-2. 0 m,and controlled by groundwater and aridity index when the water table depth is 2. 0-2. 5 m,but only controlled by aridity index when the water table depth is more than 2. 5 m. The monoexponential decay function can fit the cave between the groundwater and Ta / Tp ,whose correlation coefficient is a- bove 0. 99. On this basis,the critical water table depths are determined in normal,low and high flow year. The critical water table depths vary in different hydrological years and the vegetation will suffer from water stress when the water table depth is more than 1. 24 m (average),and degenerate when the water table depth is more than 2. 06 m ( aver- age). Meanwhile,the effects of the decline in the water table caused by coal mining on the transpiration of typical veg- etation is limited. The decline in the water table caused by coal mining has effect on vegetation when the initial pre- mining water table depth is less than 2. 5 m. However,there has little effect on vegetation when the initial pre-mining water table depth is more than 2. 5 m,the transpiration is only controlled by climate change at this moment. At pres- ent,the main factor that affects the vegetation coverage is climate change (precipitation) because the initial pre-min- ing water table depth is generally greater than 2. 5 m in Yushen mining area. Therefore,the vegetation coverage increa- ses although the water level decreases obviously considering the increasing trend of precipitation in recent years.