IMPACT OF CLIMATE CHANGE ON GROUNDWATER RECHARGE IN HO CHI MINH CITY AREA

Groundwater is very important for the development of Ho Chi Minh City since it provides 32% of water supply, however, the groundwater level is decreasing dramatically in recent years due to the socio-economical demand. Moreover, groundwater in Ho Chi Minh City is directly impacted by climate factors such as precipitation, evapotranspiration, and river water stage. However, the study of climate change impact on groundwater for the area is just in the starting stage. The study presented the application of groundwater model (MODFLOW) using Global Climate model (GCM) data to study the impact of climate change on groundwater recharge in the area. Global Climate Model (GCM) named MRI-AGCM3.2s is used to project precipitation and temperature for the area in two future timeframes, i.e., near future (2015-2039) and far future (2075-2099). Bias-correction method exhibited ability of reducing biases from the frequency and amount when compared with observed and computed values at grid nodes; based on spatially interpolated observed rainfall data. Groundwater model is applied to estimate historical recharge rate (1995-2007) and develop recharge function as well as groundwater simulation, to determine the impacts of climate towards groundwater recharge. Calibration groundwater model is implemented during 1995-2007 and verification groundwater model during 2008-2012. Calibrating and verifying groundwater model show that the simulation result is more reasonable when using recharge rate function with effective rainfall and with the recharge function, the impact of climate factor such as precipitation and temperature on groundwater recharge can be examined in the future. Two cases of future groundwater simulation were conducted such as with/without sea level rise to assess the impacts. As a result, future groundwater simulations show that groundwater resources in the area will be impacted by climate change and sea level rise. Groundwater recharge from land surface will decrease 17% in the near future due to more evapotranspiration and recover in the far future period due to more precipitation. Besides, climate change and sea level rise will increase groundwater level in the future, however, it also leads to the increase possibility of salt water intrusion in the same time. For groundwater management improvement, this study simulated future groundwater conditions by controlling groundwater pumping. The results show that groundwater pumping reduction of 41% in the near future and 56% in the far future can make groundwater level increase 2.86 m in the near future period and 4.56 m in the far future period, and decrease 41% and 56% of salt water flow from salt water zone to fresh water zone in near future and far future, respectively.