Numerical modeling applications for the evaluation of the past and future scenarios of groundwater use in an urbanized complex karst aquifer in the city of Sete Lagoas, State of Minas Gerais, Brazil

Karst aquifers provide substantial drinking water resources, resulting in faster urban growth. However, excessive pumping may lead to some consequences such as overexploitation, resulting in land subsidence, large cones of depression, or the drying up of springs and surface water. A FEFLOW numerical model was developed to evaluate the hydrodynamic evolution and future strategies for sustainable use of Brazil's overexploited Sete Lagoa Karst Aquifer System. The dataset consists of more than 250 locations of hydraulic heads and discharge rate measurements, geological maps, historical hydraulic head distributions, and hydraulic conductivity (K) and storage (Ss, Sy) data of different scales. Upon calibration, a satisfactory degree of correspondence between observed and simulated heads (RMSE between 5 m and 19 m, and MAE between 4 m and 23 m) was obtained. The calibrated K (2; 20; 0.0035 m/d), Ss (9.0 × 10 −3 ; 9.0 × 10 −3 ; 4.5 × 10 −3  m −1 ), and Sy (2.5 × 10 −1 ; 5.0 × 10 −1 ; 1.5 × 10 −2 ) for epikarst, karstified zones, and limestone matrix, respectively, along with recharge rates, are consistent with measurements and the conceptual understanding of the system. The model shows the mean annual recharge is currently 29% of the precipitation (∼51 Mm 3 /yr or 12 L/s/km 2 ), and the total discharge in wells is 30% of the precipitation (53 Mm 3 /yr or 13 L/s/km 2 ), implying ongoing water deficit, leading to the expansion of a significant cone of depression (∼29 km 2 ) centralized in a densely populated area. The intense pumping caused an increase in unconfined conditions, from 34% of the area in 1942 to 45% in 2020. Maintaining the multi-year average precipitation (1307 mm/yr) and calibrated recharge rates constant, if the current pumping rates persist, more than 50% and 61% of the aquifer would become unconfined in 2050 and 2100, respectively, further exceeding the risks of land subsidence. A new equilibrium condition can be achieved with a 40% reduction in the total pumping rate.