Evaluating the impacts of climate change and water over-abstraction on groundwater resources in Pacific island country of Tonga

Small low-lying Pacific Island countries are prone to climate change and water resources-related issues. The demand for water in Pacific Island countries has increased significantly due to population growth, industrialisation, tourism, and agricultural needs. Groundwater is utilised by most of the Pacific Island countries, and due to increasing demand, the majority of the Pacific Island countries practise over-abstraction. Climate change caused by natural means and over-abstraction of groundwater has led to saltwater intrusion into the coastal aquifers and other groundwater-related problems in several low-lying Pacific Island countries. In this study, groundwater salinity data collected over a 42-year duration from several abstraction wells in Tonga is linearly analysed to ascertain the impact of over-abstraction on groundwater resources. Climate change also affects rainfall and net recharge patterns. Hence, Tonga's long-term rainfall and net recharge patterns were linearly analysed. Also, to ascertain the climate change effect in Tonga, the sea level height and carbon dioxide emissions were linearly analysed using the data from 1993 to 2020 and 1960–2018, respectively. Quantitative data, linear regression and graphical linear fit techniques were used in this study for data analysis. The results from this study indicated that over-abstraction has caused saltwater intrusion more frequently and affected groundwater quality. An increasing salinity trend of 58% was observed from 1965 till 2007. It is also evident that the higher the abstraction rates, the higher the saltwater flux sipping into the coastal aquifers. Moreover, decreasing trends were also observed in rainfall (19%) and net recharge (37%) in Tonga between 1950 and 2006. This study also revealed that the sea level and carbon dioxide emissions have increased by 5.2% and 800%, respectively. This study provides insights into why controlling abstraction rates and acting against climate change is essential concerning groundwater. These insights will be helpful for groundwater resource managers, stakeholders, and policymakers in Tonga and the broad scientific community, in managing saltwater intrusions and preserving the water resource.