Modelling shallow groundwater fluctuation based on water table depth – groundwater evapotranspiration relationship

Fluctuation of shallow groundwater (GW) characteristic in plains and lowlands is regulated by recharge from precipitation and groundwater evapotranspiration under natural conditions. Here a simple 1D (pointwise) model is presented that is capable of reproducing the dynamics of shallow GW levels at monthly, weekly or even daily time scale at the location of groundwater level monitoring wells using precipitation and potential evapotranspiration as input variables. The model utilizes the empirical curve describing the dependence of GW evapotranspiration on the depth of water table, revealed by analyzing historical measured GW level and evapotranspiration time series in the Great Hungarian Plain. Besides GW levels, the model calculates groundwater recharge and evapotranspiration. Soil and hydrological parameters of the model are calibrated based on measured GW levels.

Potential fields of application of the model are shown through Hungarian examples: 1) Using precipitation and potential evapotranspiration data of various climate models, expected alterations of shallow GW levels due to climate change can be predicted. 2) By comparing measured and simulated GW levels, alterations in GW levels and fluctuation due to anthropogenic activity (e.g. GW abstractions) can be revealed. 3) Data gaps in measured GW level time series can be filled by the model. 4) Extending the time series of measured GW levels into the past allows for historical analyses, e.g. the temporal changes of GW supply of dependent ecosystems.