Modeling and application of groundwater-dependent ecosystems (GDEs) using PARFLW-CLM in the Edward aquifer area, Texas

Groundwater-soil-plant-atmosphere interaction has an important role in the climate cycle, surface/subsurface water management, and ecosystem function. However, physiological activities, such as transpiration from deep groundwater (e.g., phreatophytic vegetation), are often neglected in the prediction. The groundwater model frequently simplifies the recharge function (e.g., river, precipitation), and ignores unsaturated water flow. Texas is sustainably managing groundwater through the groundwater availability modeling (GAM) program and MODFLOW simulation, but the MODFLOW model is known to have those simplification issues.

In our previous study, a phreatophytes function was successfully applied to PARFLW-CLM about a site in California. Here, we extended the preceding study to the Texas region (Edwards Aquifer) to examine the role of groundwater-dependent ecosystems (GDEs) and to test an advanced groundwater model. The Edwards Aquifer area is known for having a high portion of GDEs. PARFLOW-CLM is a more complex groundwater model compare to MODFLOW, which considers the detailed mechanism of land-atmosphere interaction, surface hydrology (routing), and unsaturated water flow. We applied the updated PARFLOW-CLM model to reflect phreatophytes activity and used a routing function (surface water flow) rather than the constant recharge rates normally used in MODFLOW.

This study highlights the importance of detailed processes such as surface hydrology, the role of the unsaturated zone, and deep root functions in the model. The routing function and canopy process (CLM) has an influence on the recharge rate. We can also identify how much the deep root function (physiological activities) affect ET rate and groundwater availability. The application of such mechanisms would provide a more realistic/accurate prediction for the water cycle and water resources than a simplified model, especially linking with the various surface conditions (e.g., weather, land-use, policies).