5.1 Impact of GLF on the water table
Changes in groundwater heads due to activities such as the over-exploitation of groundwater can lead to a decline of the groundwater table and depression cones near wells (Chen et al. 2003, 2011). These can cause changes in the lateral flow, which naturally transports groundwater from surrounding areas to local groundwater depressions. This process plays a critical role in offsetting the loss of locally stored water, and in relieving the negative effects of overexploitation on the eco-hydrological system. The addition of the GLF process allowed for the consideration of the lateral flow, which has been shown to be an important process, especially for the simulation of hydrological variables. Figure 9 shows the simulated equilibrium water table depth with and without GLF (EXP and CTR, respectively), and their difference, for the years 1979–1999. Apparent modification of the groundwater by the GLF module was seen in these figures; the water tables in North Africa, Arabian Peninsula, parts of central Asia, and southern Australia have deepened. Among these, the largest can be seen in North Africa, where the largest depth reached 50 m below ground; small parts of northern India also showed similar deepening phenomena. In other regions, such as the western coast of North America and Australia, the deepening rate was smaller, with values of 35 m and 12 m, respectively. This increased spatial variability of the modeled groundwater table depth in the EXP run may result in differences in the bio-geophysical and bio-geochemical aspects of the land surface (e.g., land atmospheric coupling, water extraction of the vegetation, etc.), and thus had potential effects on the climate process under climate warming.