Explore historical and projected climate data, climate data by sector, impacts, key vulnerabilities and what adaptation measures are being taken. Explore the overview for a general context of how climate change is affecting Tonga.

Impacts Water

According to the World Bank, since 2008, 100% of the people residing in rural areas of Tonga have had access to improved water and sanitation. However, as with many other Small Island Developing States and Pacific Island Countries (PICs), Tonga’s small size, minimal amount of storage, and limited fresh water render it highly susceptible to threats to fresh water availability and groundwater supplies are threatened by salt-water intrusion as a result of increasing sea levels.  The two main sources of water in Tonga are from rainwater collected and stored in cisterns as well as the freshwater lens found in highly porous limestone substrate. Surface water resources are not commonly present in Tonga, with the exception of the coral island of Eua and a number of volcanic islands including Niuafo’ou and Tofua (Ha’apai Island), and a large number of small islands in Ha’apai and Vava’u that rely entirely on rainwater tanks for their water. As with most other PICs, Tonga’s dependency on rainfall increases its vulnerability to future changes and distribution of rainfall. Low rainfall can lead to a reduction in the amount of water that can be physically harvested and a slower rate of recharge of the freshwater lens, which can result in prolonged droughts. Since most of the islands are dependent on surface water catchments for their water supply, it is likely that demand cannot be met during periods of low rainfall.   The wet and dry cycles associated with El Nino Southern Oscillation episodes can also deliver serious impacts on water supply in Tonga as well as the other PICs, highlighting the vulnerability of water supplies to changes in the climate. For instance, the strong El Niño of 1998–2000 was responsible for acute water shortages in many islands in the Pacific Ocean. Further vulnerabilities arise under future climate-induced droughts, as there is no centralized reticulated sewerage system in Tonga and poorly constructed or inappropriate sanitation systems are common, resulting in the potential for pathogens and nutrients being introduced into the surrounding environment, including ingress to groundwater.

This section provides insights into projected climate change impacts on various hydrological indicators.


Data presented under Historical Climate Conditions are reanalysis products derived from ERA5-Land data. ERA5-Land is a global land-surface dataset at 9 km resolution, consistent with atmospheric data from the ERA5 reanalysis from 1950 onward. Climate reanalyses combine past observations with models to generate consistent time series of multiple climate variables. They provide a comprehensive description of the observed climate as it has evolved during recent decades, on 3D grids at sub-daily intervals. 

This data has been collected, aggregated and processed by the Climate Resilience Cluster of the European Space Agency’s (ESA) Earth Observation for Sustainable Development (EO4SD) initiative.