Climate Change Impacts on Water Security in Palau, Tonga, and Timor-Leste

UNSW’s analysis found that Palau has sufficient water resources for its population, but variability in the annual and interannual water availability, as well as limitations in supply and distribution networks, and water quality concerns, make the nation vulnerable to climate change hazards. Water availability in Palau’s outer islands is limited and water scarcity is common during droughts, particularly during El Niño events. An assessment of Palau’s water resources and climate change analysis show that Palau’s water systems are already vulnerable to climate change, and that saltwater intrusion has impacted food production. Meanwhile, there is concern of combined loss of coastal ecosystems and sea level rise causing larger impacts on coastal flooding. 

The future climate impact assessment estimates that in future, drought severity will increase, and total annual water availability will reduce to critical levels more frequently. This will place increased pressures on the Ngerimel and Ngerikiil water resources, causing a substantial decrease in reliability for these sources that will impact 75% of the population of Palau. The increase in extreme rainfall intensity will likely cause cascading problems of increased erosion and sedimentation, damaging marine ecosystems, which could reduce the effectiveness of natural coastal defences to sea level rise and coastal flooding.  The risks to groundwater dependent outer islands are impacted by geography, island hydrogeology, and the rate of sea level rise.

The assessment determined priority areas for adaptation investment, and the recommended interventions include:

• Implementing improved hydrological monitoring, including new data gauges for rainfall, streamflow, and evapotranspiration
• Increasing rainwater harvesting capacity and developing additional rainwater storage infrastructure
• Improving efficiency of the Koror-Airai water distribution system to reduce losses and optimize resource use
• Improving water quality monitoring and treatment
•  Integrated Water Resource Management (IWRM) and Ecosystem-based Adaptation approaches, including reforestation, sedimentation control and coastal restoration
•  Improving rural sanitation provisions
• Implementing sustainable agriculture and aquaculture practices crucial to implementing Ecosystem-based Adaptation approaches
• Enhanced water security on Peleliu and Kayangel through increased rainwater harvesting, sustainable groundwater management, and exploring desalination as a supplementary water source.

Tonga is ranked among the most disaster-prone nations globally due to its high exposure to natural disasters, rising sea levels, and limited adaptive capacity. It faces many challenges from climate change, particularly sea level rise, which is occurring at a rate exceeding the global average. The low elevation of many of Tonga’s islands amplifies their vulnerability to inundation and storm surges, infrastructure damage, groundwater salinization, and population displacement.

By 2051, routine flooding in the capital city of Nuku’alofa is projected under moderate sea level rise, with chronic flooding expected by 2059. Rainfall projections for Tonga are highly uncertain due to disagreement among climate models, but in a dry future scenario, dry season rainfall could decrease by up to 15% in the mid-term, severely impacting water availability in already drought-prone islands. With most of Tonga’s islands lacking surface water resources, water supply is highly dependent on rainwater harvesting and groundwater from freshwater lenses. The heavy dependence on rainfall makes communities particularly vulnerable to droughts and unpredictable climate patterns.  Agriculture, a cornerstone of Tonga’s economy, is primarily subsistence and semi-subsistence based, making it especially vulnerable to climate impacts.

To enable sustainable access to high-quality water while protecting ecosystems critical to the nation’s resilience and livelihoods, recommended interventions include:

• Expanding rainwater harvesting infrastructure to meet future water demand, and combining residential rainwater harvesting with improved business water systems to increase water security during dry periods.
• Establishing and maintaining comprehensive groundwater monitoring
• Developing models and frameworks to predict the impacts of droughts on freshwater lenses and disseminating information to residents
• Providing advice on suitable crops for seasons, ensuring resilient crops for dry conditions, and investigating the expansion of irrigation systems to address increased rainfall variability and dry season rainfall shortages. 
• Protecting mangrove ecosystems to maximise coastal protection against storm surges and sea level rise
• Improving water quality monitoring of freshwater lenses to identify sources of pollution and maintain protection zones. 
• Establishing and maintaining water quality monitoring systems for rainwater harvesting systems.

Throughout Timor-Leste, around a quarter of households lack access to safe drinking water. In rural areas, almost 20% of the population lacks access to basic water services, and more than half lacks access to basic sanitation (INETL 2023). Timor-Leste is highly vulnerable to the impacts of climate change due to significant interannual rainfall variability, high exposure to droughts, floods, and landslides, and a low economic status that reduces its adaptive capacity. Across all municipalities, seasonal variability heavily impacts water resources. Over-reliance on wells and springs leads to resource depletion and quality issues, while underdeveloped rainwater harvesting infrastructure limits its potential to supplement other sources. Flooding and sedimentation during the rainy season further reduce the reliability of rivers. Crop yields in Timor-Leste are significantly lower than the averages in other Southeast Asian countries, and droughts pose significant threats to agriculture. The baseline climate assessment highlighted that the major climate-related risks to water resources in Timor-Leste include changes to rainfall seasonality and an extended dry season.

Climate projections from an ensemble of regional models indicate a substantial decrease in dry season rainfall. The volume of precipitation during the dry season is projected to decrease, while the number of dry days is expected to increase. These changes will heighten Timor-Leste’s vulnerability to drought, with direct impacts on water availability for human consumption and agriculture. Both surface water and groundwater availability are expected to decline during the dry season, and surface water availability is at significantly at risk. Additionally, population growth and increases in demand for irrigation water, combined with the expansion of agricultural activities, will further strain Timor-Leste's limited water resources.

To ensure sustainable access to high-quality water while protecting ecosystems, the recommended interventions include:

• Establishing hydrological monitoring systems for rainfall, water levels, water quality, and spring extractions to improve data reliability, enable adaptive surface water management, and prepare communities for droughts.
  
  
• Expanding rainwater harvesting infrastructure in vulnerable regions, improving water quality monitoring, and promote community preparedness for droughts.
  
  
• Providing timely climate information, promoting resilient agricultural practices, and integrating climate education into schools and public campaigns to increase preparedness for drought impacts.
  
  
• Implementing Community-Based Water Resources Management, including restoring and reforesting catchments, implementing sustainable land use practices, and fostering community participation to enhance water infiltration, quality, and availability while promoting sustainable agricultural practices.