The purpose of this study is to delineate the main contributions controlling the chemical composition of groundwater and spring water samples at Jeju Island, South Korea. Groundwater and spring water can be grouped as three chemical types: Fresh water (Ca, Na-HCO₃), sea water mixing (Na-Cl, SO₄) and contamination (Ca-NO₃, Cl). By factor analysis, three factors can explain about 87% of chemical variances: Factor 1 (Na⁺ and Cl⁻), factor 2 (NO₃⁻), and factors 3 (HCO₃⁻), which are regarded as indicative ions of sea water mixing, contamination and mineral-water interaction, respectively. Sea water intrusion in the southeastern area of Jeju Island is due to downward distribution of Seogwipo Formation, which plays a role as an aquiclude preventing sea water intrusion in other areas, under sea level at the southeastern coastal area. Nitrate contamination is likely to be affected by pollution sources, i.e., agricultural activities, horse farms and municipal sewage. Thermodynamic saturation index indicates that most of waters are undersaturated with respect to major minerals, which may result from insufficient reaction time within a permeable aquifer. The unsaturation state corresponds to low load scores of Ca, Mg, Na, K, and SiO₂ in factor 3, which means a low contribution of mineral-water interaction.

Thermal water from the hot springs around Bugok, South Korea, has the highest discharge temperature (78 °C), and the source of that heat is of primary interest. The key ³He/⁴He ratio runs along a single air-mixing line between the mantle and the crust, with the latter accounting for 97.0–97.3%. This suggests that the thermal source is radioactive decay in granodiorite, rock that intruded beneath the Cetaceous era sedimentary rock. Thermal water containing Na–HCO₃ (SO₄) evolved geochemically from stream water and groundwater containing Ca–HCO₃. With respect to δ³⁴S, there are two types of thermal water: low temperature with low δ³⁴S (−3.00~+1.00‰), and high temperature with high δ³⁴S (+4.60~+15.0‰), which is enriched by the kinetic fractionation of H₂S. The thermal water samples, except for a few, reached partial chemical equilibrium. The thermal reservoir temperatures were estimated as in the range of 90–126 °C by the K–Mg geothermometer of Giggenbach and the thermodynamic equilibrium of quartz and muscovite. This study suggests a conceptual model for the formation of geothermal water, including the thermal reservoir in the Bugok area.

Based on the climate change adaptation report, South Korea's annual mean temperature in the late 21st century is likely to rise by 2.3 to 6.3 °C compared to current levels, while annual average precipitation is expected to rise by 4 to 16 % relative to the current mean. Increased precipitation reduces frictional resistance and elevates moisture content in slopes, increasing the strain on top slope sections and greatly increasing the potential of landslides.Under Article 32-6 of the Republic of Korea's Forest Protection Act Enforcement Decree, landslide warning system are classified into three stages: advisory, preliminary warning, and warning, based on soil moisture limits of 80, 90, and 100%, respectively. Nonetheless, soil moisture is heavily influenced by site-specific soil features like permeability and groundwater level, limiting its capacity to anticipate localized conditions.In order to secure a golden time for readiness through early prediction of landslides, which are highly sensitive to climate change, and to reduce casualties by evacuating residents quickly and safely, the Korea Forest Service launched a field-response technology development project in 2025. The goal of this project is to build technology for AIoT-based real-time risk monitoring, an audio-visual warning system, and evacuation-route guidance to optimize safe evacuation from landslide. For this research, a test site was chosen in the Triassic granite area of Cheongsong, Gyeongsangbuk-do, South Korea. The project involves setting up in-situ soil moisture measurement devices, developing a next-generation alram technique that combines audio-visual warning devices with soil moisture measurement, and building an early warning system with a LoRa-based IoT wireless sensing network. AcknowledgementThis study was conducted with the support of the R&D program for Forest Science & Technology (No.RS-2025-02233085)