Interaction between groundwater and trees in an arid site: Potential impacts of climate variation and groundwater abstraction on trees Lihe Yin a,b,⇑ , Yangxiao Zhou b , Jinting Huang a , Jochen Wenninger b,c , Eryong Zhang d , Guangcai Hou a , Jiaqiu Dong a a Xi’an Center of Geological Survey, China Geological Survey, No. 438, Youyidong Road, Xi’an 710054, China b UNESCO-IHE Institute for Water Education, P.O. Box 3015, 2601 DA Delft, The Netherlands c Delft University of Technology, Faculty of Civil Engineering and Geosciences, Water Resources Section, Stevinweg 1, 2628 CN Delft, The Netherlands d China Geological Survey, No. 45, Fuwai Street, Beijing 100037, China article info Article history: Received 31 March 2015 Received in revised form 10 June 2015 Accepted 28 June 2015 Available online 2 July 2015 This manuscript was handled by Peter K. Kitanidis, Editor-in-Chief, with the assistance of J. Simunek, Associate Editor Keywords: Groundwater use Tree water uptake Arid regions HYDRUS-1D Stable isotopes Groundwater abstraction summary The understanding of the interaction between groundwater and trees is vital for sustainable groundwater use and maintenance of a healthy ecosystem in arid regions. The short- and long-term groundwater con- tribution to tree water use was investigated using the HYDRUS-1D model and stable isotopes. For the short-term simulation, the ratio between the actual transpiration (T a ) and potential transpiration (T p ) approached almost 1.0 due to the constant groundwater uptake. The results from the short-term sim- ulation indicated that the groundwater contribution to tree water use ranged between 53% and 56% in the dry season (May–June) and 16–19% in the wet period (August–September). Isotopic analysis indicated that groundwater contributed to 45% of plant water use in the dry season, decreasing to 4–12% during the wet period. Because of canopy interception and transpiration, groundwater recharge only occurred after heavy rainfall and accounted for 3–8% of the total heavy rainfall. For the long-term simulation, T a /T p ranged between 0.91 and 1.00 except in 2007 (0.78), when the water table declined because of groundwater abstraction. In the scenario simulation for deep water table conditions caused by anthro- pogenic activities, T a /T p ranged between 0.09 and 0.40 (mean = 0.22) that is significantly lower than the values in the natural conditions. In conclusion, vegetation restoration in arid zones should be cautious as over-planting of trees will decrease the groundwater recharge and potentially cause a rapid drop in water table levels, which in turn may result in the death of planted trees. Trees adapt to arid regions by adopting root patterns that allow soil water uptake by shallow roots and groundwater use by deep roots, thus climatic variation itself may not bring severe negative impact on trees. However, anthro- pogenic activities, such as groundwater abstraction, will result in significant water table decline that will reduce actual transpiration of trees significantly according to the results from the scenario simulation. Ó 2015 Elsevier B.V. All rights reserved. 1. Introduction Arid regions cover about one third of the Earth’s land surface and are inhabited by almost one billion people (Yin et al., 2013). In arid environments, trees play a significant role in maintaining those environments suitable for agriculture and humans (Malagnoux et al., 2007) by providing natural protection against desertification (Tucker et al., 1991) and reducing poverty and food insecurity (Schreckenberg et al., 2006). Therefore, the majority of the newly afforested 100 million hectares during the period of 2000–2010 is located in arid zones and particularly in arid zones of China (FAO, 2010). As an example, several large-scale ecological restoration projects have been carried out in Chinese arid regions, including the Three North Shelter Belts Forest, the Grain for Green, and the Natural Forest Conservation projects (Cao, 2011). Water, including surface water, groundwater, and soil water, is vital for tree growth (Zhu et al., 2009 and Richard et al., 2013), with groundwater being an important source in arid regions as it is rel- atively constant and stable. Many trees in arid regions are reported to be groundwater-dependent (Bulter et al., 2007 and Gribovszki et al., 2010) and they can obtain large amounts of groundwater for transpiration through deep roots, especially during dry seasons (David et al., 2007 and Lubczynski, 2009). The contribution of groundwater to plant water use has been studied for a long time, with a pioneering study from White http://dx.doi.org/10.1016/j.jhydrol.2015.06.063 0022-1694/Ó 2015 Elsevier B.V. All rights reserved. ⇑ Corresponding author at: Xi’an Center of Geological Survey, China Geological Survey, No. 438, Youyidong Road, Xi’an 710054, China. Tel.: +86 29 87821986; fax: +86 29 87821978. E-mail address: ylihe@cgs.cn (L. Yin). Journal of Hydrology 528 (2015) 435–448 Contents lists available at ScienceDirect Journal of Hydrology journal homepage: www.elsevier.com/locate/jhydrol