Identifying the Relationship Between Plant Transpiration and Groundwater Table Depth

Abstract:

Impact of the groundwater on plant transpiration constitutes an important but not well understood aspect of the interactions between groundwater and the land surface, vegetation and atmosphere. The lack of understanding can be attributed to the limited observations and the complex nature of the problem as the mechanisms and processes involved are many and often tightly coupled. This study addresses such issues by using the Variable Infiltration Capacity Plus (VIC+) land surface model (LSM) in conjunction with a series of numerical experiments. The VIC+ model considers impacts of the hydraulic redistribution (HR), plant storage, photosynthesis, and groundwater table (GWT) dynamics on plant transpiration, and the interactions between plant transpiration and subsurface processes. Several groups of numerical experiments are performed using different combinations of precipitation conditions, vegetation types, soil types, groundwater table depths (GWTDs) and treatment of the HR process. We have found, in water limited climates, vegetation type, soil type and the HR process have strong impacts on transpiration – GWTD relationships. In particular when the HR is significant, such as in drier climates, the inclusion of HR process in the modeling is essential in establishing the correct relationship between the plant transpiration and GWTD, where an omission would result in a more linear-like relationship. In addition, under certain conditions, there exists a transition zone in the relationship between plant transpiration and GWTD, where transpiration drops abruptly as the groundwater table declines. Moreover, plant transpiration and groundwater become disconnected as the groundwater table declines further and lies below the transition zone.