Analysis of tropical urban aquifers in response to climate change

Urban aquifers represent an undeveloped resource and utilization is also arising as a method to improve storm water management. In dry climate, these aquifers are an alternative water supply source and in tropical climate can mitigate waterlogging and floods. However, sources and pathways of urban groundwater are more numerous and complex than those in rural environments. Furthermore, climate change and more frequent and intense climate extremes increase the variability in precipitation, soil moisture, and surface water. Therefore, a long-term effective urban water management is imperative.

This study investigates the groundwater in Shenzhen, a major financial and high-tech center in southern China, along the left side of the Zhujiang Estuary (Pearl River Delta). Shenzhen has a population of about 14 million permanent residents and currently has a total water consumption of 2 billion m³ per annum. Previous research has investigated the hydrogeological setting and groundwater budgets via numerical flow simulations under steady-state conditions. In the present research, a MODFLOW transient model has been constructed to estimate the groundwater budgets in Shenzhen in response to projected climate change.

Model conditions are varied, considering the typical Representative Concentration Pathway (RCP) scenarios (RCP 2.6, RCP4.5, RCP 6.0 and RCP 8.5) from 2019 to 2049. Simulations are grouped into two numerical analyses. For the first analysis, the rainfall rate decreases by 37.4% (RCP2.6, RCP4.5) together with a sea-level increment of 0.36 m (RCP 4.5); for the second analysis rainfall increases by 11.82% (RCP 6.0, RCP 8.5) and a sea-level increment of 0.5 m (RCP 8.5).

In the first analysis (RCP 2.6, RCP 4.5) the groundwater budget decreases by approximately 26% within the study domain, and the water table declines from 1 to 26 m. The second analysis shows a 15.48% increase in the groundwater budget, as the water level rises on average from 0.5 to 8 m. Given the sensitivity of the model results to the choice of future climate scenario, this study indicates the importance of accurate climate change predictions to help local authorities better manage water resources in tropical urban aquifers.