What are the Subsurface Environmental Problems?

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Subsurface environmental problems, such as land subsidence, groundwater contamination, and subsurface thermal anomalies, are important aspects of human life in the present and future but have not been evaluated as yet. Interactions between surface/subsurface and subsurface/coastal environments under the pressures of climate variability and human activities have been ­analysed for the cities of Tokyo, Osaka, Bangkok, Manila, Jakarta, Taipei, and Seoul, which are in different stages of urbanization. Analyses from satellite GRACE data showed that land water storage in Bangkok decreased since 2002. Groundwater tracers and 3D numerical simulations of groundwater showed that the groundwater flow system­ in the urban aquifer has been highly disturbed by pumping, causing a vertical downward flux in the urban area. Subsurface temperatures observed in the study cities illustrate the magnitude and timing of surface warming due to global warming and heat island effects. The amount of the increase in surface temperature was found to be larger in the city center than that in suburban and rural areas, reflecting the degree of urbanization. Contamination histories in each city have been reconstructed from sediment studies of nutrient and heavy metal contaminations. Analyses of land cover/use changes show that urbanization caused a reduction of groundwater recharge and an increase in thermal transfer into the subsurface environment. Two groups of integrated indicators: (1) natural capacities; and (2) changing society and environments, were used to analyse the relationships between the developmental stage of the city and the subsurface environment. Comparing Tokyo with each city shows that some cities have a benefit by developing later and/or benefit from a natural capacity such as higher groundwater recharge rate as higher input to aquifer. However, excessive development in Jakarta causes severe damage by land subsidence. Groundwater and subsurface environments should be investigated for their adaptation and resilience to changing environment conditions. In addition, subsurface environments should be treated together with surface and coastal environments for better management and sustainable use.