Nakdong River Basin Research Articles

Drought risk assessment for future climate projections in the Nakdong River Basin, Korea

AbstractTo prepare for the potential of extreme drought caused by climate change, both physical and socioeconomic factors need to be considered. In this study, three general circulation models were selected: IPSL‐CM5A‐LR, HadGEM2‐AO, and CanESM2 as representative scenarios for severe, moderate, and relatively weak droughts to assess the risk of droughts for future climate projections. Drought hazard was estimated using the meteorological drought index to determine drought frequency, severity, and probability. Population density, agricultural land area, and municipal, agricultural, and industrial water demand were used as drought vulnerability indicators. The Analytical Hierarchy Process technique was applied to determine the weight of each indicator, and the integrated drought risk was then estimated. HadGEM2‐AO and CanESM2 projected that drought risk would be reduced in the far future. IPSL‐CM5A‐LR projected an increased drought risk in the near and far future in the downstream area of the Nakdong River Basin. This study presented a quantitative approach to identify high drought‐risk areas that should be the focus of future extreme drought assessments and mid‐ to long‐term drought mitigation strategies.

Processes and characteristics of hydrogeochemical variations between unconfined and confined aquifer systems: a case study of the Nakdong River Basin in Busan City, Korea.

This study is to assess the hydrogeochemical characteristics of groundwater at the deltaic region of the Nakdong River Basin in the Busan Metropolitan City of Korea. The study area is covered by the Quaternary sedimentary deposits and the Cretaceous granites associated with unconformity. The thick sedimentary deposits consists of two aquifers, i.e., unconfined and confined aquifers on the basis of clay deposit. Groundwater samples were collected from seven boreholes: two from unconfined aquifer and five from confined aquifer systems during the wet season of 2017year. ORP and DO indicates thatthe groundwater of the unconfined aquifer exists in the oxidization condition and that of the confined aquifer pertains in the reduction condition. Piper's trilinear diagram shows CaSO4 type for groundwater of the unconfined aquifer, and NaCl type for that of the confined aquifer. Ionic concentrations of groundwater increase in the confined aquifer because of direct and reverse ion exchange processes. Carbonate weathering and evaporation are other mechanisms in the water-rock interaction. Saturation indices of dolomite and calcite are observed as oversaturated, while halite reveals undersaturation. Hierarchical cluster analysis (HCA) exhibitsthat cluster 1 and cluster 2 represents the properties of groundwater in unconfined and confined aquifers, respectively. Factor analysis shows that groundwater of the confined aquifer is much influenced by seawater, and includes heavy metals of iron and aluminum. Groundwater samples in unconfined and confined aquifers are located at the rock weathering and evaporation zones in the Gibbs diagram. Inverse geochemical modeling of PHREEQC code suggests that carbonate dissolution and ion exchange of major ions are the prevailing geochemical processes. This comprehensive research provides the distinguished hydrogeochemical characteristics of groundwater in confined and unconfined aquifer systems of the Nakdong River Basin in Busan City, Korea.

Spatial Distribution Patterns of Eurasian Otter (Lutra Lutra) in Association with Environmental Factors Unravelled by Machine Learning and Diffusion Kernel Method

In South Korea, the endangered Eurasian otter (Lutra lutra) populations have been recovered throughout the country. To examine the status of otter populations, we monitored spraint densities at 250 ~ 355 sites annually from 2014 to 2017 in the Nakdong River basin. The diffusion kernel method was applied to both binary and continuous spraint data. Two geographical popula - tions were identified: northern and southern populations. The northern population continuously increased over a broad area from north to south during the study period. In contrast, the southern population narrowly dispersed, limited by its location in an industrial area. The spatial self-organizing map (Geo-SOM) revealed associations between spraint densities and environmental factors by correlating the geographic locations of the sampling sites. Both populations were negatively affected by anthropogenic factors, including proximi - ty to factories and human population density. However, cumulative association of all environmental factors, including landscape, food sources, and anthropogenic factors, were noted in 2016 after which otter populations fully recovered. Population development stabilized while exhibiting an overall high association with environmental factors. The results of the diffusion kernel method and data variation according to the Geo-SOM consistently presented substantial change in population dispersal (i.e. the merge of two subpopulations, and complete associations between spraint and environmental factors). The combination of the diffusion kernel method and Geo-SOM was effective in portraying temporal changes in population states in association with environmental factors based on spra int data in the last phase of full recovery.

낙동강 유역의 SPI 예측을 위한 심층신경망 개발 및 검증

본 연구에서, 낙동강 유역의 SPI6를 예측하기 위해 신경망 모형 중 하나인 다층 퍼셉트론 (MLP; multilayer perceptron)을 적용했다. 월별 표준강수지수, 기온, 기온 평년값, 강수량, 강수 평년 값, 강수 일수, 그리고 여러가지 세계기후지수를 설명 변수로 사용했으며, 최적의 모형을 찾기 위해 두 가지의 활성함수, 네 가지의 은닉층별 뉴런 수, 다섯 가지 중도탈락 비율 (dropout rate), 다섯 가지 은닉층 수, 두 가지 손실 함수를 고려하였다. 모형 평가 기준으로 검증평균제곱오차 (validation mean square error)를 이용하여 가장 좋은 모형을 찾고자 하였다. SPI6를 예측함에 있어서, L₁ 정규화를 적용한 모형이 적용하지 않은 모형보다 검증평균제곱오차 (validation mean square error)가 항상 더 낮았으며, 대부분의 지역에서 은닉층 수가 적을수록 검증평균제곱오차 (validation mean square error)가 더 낮은 경향을 보였다.

Long-Term Variation of Runoff Coefficient during Dry and Wet Seasons Due to Climate Change

This study investigates the future long-term variation of the runoff coefficient during dry and wet seasons in five major basins in South Korea. The variation is estimated from the Soil and Water Assessment Tool (SWAT) model outputs based on an ensemble of 13 different Coupled Model Intercomparison Project Phase 5 (CMIP5) general circulation models (GCMs) in representative concentration pathway (RCP) 4.5 and RCP 8.5 scenarios. The estimates show a temporal non-considerable increase rate of the runoff coefficient during the 21st century in both RCPs, in which the trend and uncertainty of the runoff coefficient in the dry season is projected as higher than that in the wet season. A sharp contrast between the trends of the two components of the runoff coefficient is found during the dry and wet seasons. Over the five major basins, a higher increase rate of runoff coefficient is projected in the northeastern part of the Han River basin and most of the area of the Nakdong River basin. The spatial variation in the runoff coefficient change also represents a relationship with the change in the percentage of each land cover/land use type over 109 subbasins, where the correlation of the wet-season runoff coefficient is calculated as higher than that of the dry season. This relationship is expected to vary with changes in temperature and precipitation during both seasons in three future periods.

Water quality risk assessment for drought conditions: A case study of the Korean Nakdong River basin

As the frequency of drought from climate change increases and the severity of drought become worse, it is imperative to prepare appropriate countermeasures against severe droughts. Despite the severe impacts of droughts on coupled humans and environmental systems, we do not fully understand the consequences of severe droughts affecting the environment. Therefore, the present study proposed a quantitative assessment index for water quality risk for extreme droughts to improve the safety of water environment management by providing flows to areas vulnerable to the drought. The application of this study is the Nakdong River basin in Korea, which has assessed the vulnerability of water quality to severe droughts as water quality deterioration problems continue to be experienced event after the river restoration project was completed. The results of this study are expected to provide scientific environmental drought monitoring information in a changing climate.

Hydrologic Risk Assessment of Future Extreme Drought in South Korea Using Bivariate Frequency Analysis

Recently, climate change has increased the frequency of extreme weather events. In South Korea, extreme droughts are frequent and cause serious damage. To identify the risk of extreme drought, we need to calculate the hydrologic risk using probabilistic analysis methods. In particular, future hydrologic risk of extreme drought should be compared to that of the control period. Therefore, this study quantitatively assessed the future hydrologic risk of extreme drought in South Korea according to climate change scenarios based on the representative concentration pathway (RCP) 8.5. A threshold level method was applied to observation-based rainfall data and climate change scenario-based future rainfall data to identify drought events and extract drought characteristics. A bivariate frequency analysis was then performed to estimate the return period considering both duration and severity. The estimated return periods were used to calculate and compare hydrologic risks between the control period and the future. Results indicate that the average duration of drought events for the future was similar with that for the control period, however, the average severity increased in most future scenarios. In addition, there was decreased risk of maximum drought events in the Yeongsan River basin in the future, while there was increased risk in the Nakdong River basin. The median of risk of extreme drought in the future was calculated to be larger than that of the maximum drought in the control period.

A molecular approach to identifying the relationship between resource use and availability in Eurasian otters (Lutra lutra)

In South Korea, the Eurasian otter (Lutra lutra (Linnaeus, 1758)), a semi-aquatic carnivore, is found mainly in lower order streams that tend to have a low abundance of preferred prey fish species. To investigate the relationship between resource use and availability, we used DNA barcoding to identify otter diet items in 24 otter spraints (faeces) from 16 sites along the Nakdong River basin from 4 to 6 June 2014. At these sites fish availability was assessed using scoop nets and casting nets. Fish formed the bulk of otter diet, which included also frogs, mammals, and reptiles. By DNA barcoding (success rate: 72.38%), we identified 79 prey items from 105 bone remains. The diet comprised mostly fish, but frogs, mammals, and reptiles were also identified. The fish fauna and otter diet composition differed significantly. Across the study sites, members of the Cyprinidae dominated in netted samples, but occurred less frequently in otter diet. Because most Cyprinidae are fast swimmers, otters also fed on benthic fishes and frogs, suggesting limited foraging flexibility in otters and specialization on more slowly moving prey.

Evaluation of stream flow and water quality behavior by weir operation in Nakdong river basin using SWAT

Evaluation of stream flow and water quality behavior by weir operation in Nakdong river basin using SWAT

Quantitative vulnerability assessment of water quality to extreme drought in a changing climate

Abstract Projected changes in the global climate indicate warmer temperatures and a highly variable hydrologic cycle, portending significant societal effects, particularly those stemming from drought. Whereas the extent of drought-related effects ranges from humans to environmental systems, the impacts on water quality, in particular, require careful investigation. Such investigation should include the interlinkages across climate and stream quality variables and how risk translates for various watersheds, given their particularities with respect to land use, watershed characteristics, and infrastructure. To this end, this study investigated drought assessment and the water quality vulnerability to severe drought, with the goal of informing planning and mitigation as a means to enhance drought resilience. This study was conducted in the Nakdong River basin in South Korea, which is vulnerable to water quality degradation during severe drought. We propose a method to evaluate spatial-temporal droughts based on the water quality risk and to monitor environmental droughts using the probability of exceeding the target water quality to facilitate a resilient proactive response. The results of this study can be used to provide scientific drought monitoring information for assessing real-time water quality monitoring from meteorological drought information. In addition, we expect to categorize vulnerable drought areas and to suggest essential management measures and tailored countermeasures at a local scale.

Effect of Climate Change on Long-term Riverbed Change using GSTARS Model in Nakdong River, Korea

Changes in rainfall patterns due to climate change will change the hydrological elements in the stream and the riverbed changes that will occur consequently. In addition, dredging and multi-functional Weir installation was finished along the Nakdong River, South Korea in 2012 as a part of the Four Major River Restoration Project. Due to the project the river became wider and deeper with deeper water depth. If the characteristics of the watershed are maintained, it will return to the pre-maintenance stream, which is the dynamic equilibrium of the stream. Also, there are very few studies comparing and analyzing changes in river basins in connection with climate change. In this study, to develop the riverbed variation technique considering the climate change in the Nakdong River Basin. The fit of the model was analyzed by using GSTARS, which is a hydraulic model, by analyzing the changes of the riverbed according to the number of stream tubes and the sediment transport equation. As a result of the study, it was found that the riverbed change was appropriate when three stream tubes were used and the riverbed change was over estimated when the stream tubes were five. The Ackers and White and the Yang equations were found to be suitable for the riverbed changes. As the flow rate increases, the change of the riverbed becomes larger and the riverbed becomes narrower.

A comparative assessment of climate change impacts on drought over Korea based on multiple climate projections and multiple drought indices

This study assesses future changes in drought characteristics in response to different emission scenarios over Korea based on multiple climate projections and multiple drought indices. To better resolve regional climate details and enhance confidence in future changes, multi-model projections are dynamically downscaled, and their systematic biases are statistically removed. Bias-corrected climate data are directly used to calculate the standardized precipitation index (SPI) and standardized precipitation evapotranspiration index (SPEI), and they are fed into a hydrological model to generate runoff used for the calculation of the standardized runoff index (SRI). The analysis is focused on changes in the frequencies and severities of severe or extreme droughts measured by the SPI, SPEI, and SRI for the Han River and Nakdong River basins. Fine-scale ensemble projections reveal robust changes in temperatures that monotonically respond to emission forcings, whereas precipitation changes show rather inconsistent patterns across models and scenarios. Temperature and precipitation shifts lead to changes in evapotranspiration (ET) and runoff, which modulate the drought characteristics. In general, the SPEI shows the most robust pattern with significant increases in both drought frequency and severity. This result is mainly due to the excessive potential ET that is hypothetically estimated without considering water availability. While the SPI based on only precipitation exhibits behavior different from that of the SPEI, the SRI that considers actual ET produces an intermediate level of changes between the SPI and SPEI. Compared to the large uncertainty of the frequency changes that overwhelm the change signal due to inconsistency across models and indices, the severity of future drought is likely to be exacerbated with enhanced confidence.

Management of organic matter in watersheds with insufficient observation data: the Nakdong River basin

Management of organic matter in watersheds with insufficient observation data: the Nakdong River basin

Evaluation of NOM Characteristics and Disinfection By-Products (DBPs) Formation Potential in Nakdong River Basin

Evaluation of NOM Characteristics and Disinfection By-Products (DBPs) Formation Potential in Nakdong River Basin

Comparison of the Hydro-Climatological Characteristics for the Extra-Ordinary Flood Induced by Tropical Cyclone in the Selected River Basins

ABSTRACT As the increased interesting on global warming and extreme water-related disasters, there are many countries which have been suffering from the extreme floods induced by tropical cyclones in East Asia. Therefore, in this study, the geographical and hydrometeolorogical characteristics and flood forecasting and warning systems in the selected basins from Thailand, Philippines, and South Korea are compared. Chao Phraya river basin, Pampanga river basin and Nakdong river basin are selected from Thailand, Philippines, and South Korea, respectively. As the results from the comparison, it was discovered that the different geographical and hydrometeolorogical characteristics delivers the different types of flood forecasting and warning systems in each basin. Due to the different geographical characteristics, the damage caused by the similar amount of monthly rainfall is different according to the historical records. This difference is expected to be caused by the different river regime coefficient and soil structures. The flood forecasting and warning systems in three basins are also different. South Korea has the centralized control system for the flood forecasting and warning, while the other basins have the more localized monitoring, forecasting, and warning procedures. In addition to the flood forecasting and warning system, according to the geographical characteristics, the density of the gauging stations is also different. The analyzed results might help the policy makers in the basins develop the adaptive flood forecasting and warning system considering the basin characteristics. In the further study, more investigation has to be done for the quantified results from the three basins.

Evaluation on the water supply stability of nakdong river basin based on future scenarios

In Korea, there are only a few cases that quantitative evaluate the impacts of climate change on water supply. Therefore, to ensure stable water supply in the future, a water resources plan is needed to establish by analyzing the scenarios that take into consideration the various situations in the future. In this study, we analyzed the changes of various situations for the Nakdong River basin, and constructed it for the future scenario. The stability of the water supply was analyzed through the analysis of water supply and demand prospect for each scenario path. We selected the areas expected to experience difficulty in supplying water supply and analyzed the scenarios of future water shortage by region and water sector. Also, the effect of increasing water supply capacity through optimal integrated operation of water supply facilities was analyzed and presented. Analysis of the results shows that there is a difficulty in supplying water due to future climate change experienced in the Nakdong River basin. Therefore it is necessary to prepare various countermeasures in order to mitigate or solve this problem.

Applying conservation easement policy to river spaces to mitigate natural hazards in South Korea

The purpose of the study was to evaluate the feasibility and efficiency of conservation easements as an alternative to existing policy for mitigating natural hazards by surveying local community perceptions prior to implementation. For this, individual awareness about land-use mitigation tools among local residents of river spaces in the Nakdong River basin in South Korea was investigated, with a particular focus on the willingness to pay (WTP) for cost–benefit analysis. The main lessons to be drawn from this paper are as follows. First, an easement represents a more efficient tool than original mitigation tools from a cost–benefit perspective and based on public preference for hazard mitigation in river spaces. Second, an analysis of the survey data shows that the social characteristics of the local residents affect local community perceptions of the establishment of conservation easements in varying ways. This should be fully considered when conservation easements are introduced in the future to mitigate natural hazards. Finally, the estimated mean annual WTP was 6.4 USD per household, and the total value of easements in the Nakdong River basin was approximately 8.2 USD per year. This suggests higher cost efficiency when compared to existing South Korean policy for natural hazard mitigation.

Improving Reservoir Operation Criteria to Stabilize Water Supplies in a Multipurpose Dam: Focused on Nakdong River Basin in Korea

Recently, torrential rain and drought have occurred in close temporal proximity and for similar durations due to changes in the spatiotemporal patterns of rainfall owing to climate change. In particular, when a drought occurs, it tends to be prolonged, making it necessary to improve the operation of multipurpose dams that not only control flooding but also serve as water supplies. In this study, standard water volume lines and action plans by response stage were improved so that water could be stored in advance of a drought instead of reservoir operation criteria set based on data from the past. The minimum water demand by use (domestic water, industrial water, and agricultural water) was also calculated. The improved reservoir operation criteria were applied to multipurpose dams in the Nakdong River Basin, and their effects were analyzed by calculating additionally secured water volumes. In the future, in case of lowered water volumes in multipurpose dams owing to a drought, the application of these improved reservoir operation criteria is expected to contribute to water supply stability by delaying entry into the drought stage and minimizing the damages caused by limited water supplies.

Assessment of regional drought risk under climate change using bivariate frequency analysis

Since water supply failure is one of the primary impacts of drought, drought risk should be quantified in the context of a lack of available water. To assess the drought risk, water supply system performance indices such as reliability, resiliency, and vulnerability are usually introduced as they correspond to primary drought characteristics, i.e., frequency, duration, and magnitude. In this study, we developed a drought risk index (DRI) through weighted averaging the performance indices derived using bivariate drought frequency analysis. We suggested two types of DRI: observed DRI (DRI_O) and designed DRI (DRI_D). DRI_O was calculated using an observed (or synthesized) time series of water shortages. DRI_D was estimated from the bivariate drought frequency curves, which are the probabilistic magnitudes of water shortages corresponding to a particular duration. The historical maximum drought event that represents the maximum DRI_O has generally been used as the target security level. However, we could establish a practically applicable target security level considering that the future water supply failure risk is represented by DRI_D. We defined regional drought safety criteria in this study by comparing DRI_O and DRI_D. Application of the criteria to the Nakdong river basin in South Korea showed that W1 (Byeongseongcheon) and W4 (Hyeongsangang) had the lowest and highest drought risk, respectively, and the drought safety criteria showed an average range of 5–20 years.

낙동강하류 기러기류(Anser spp.)의 지역별 특성

본 연구는 5년간(2008. 10- 2013. 9)의 연구 자료를 비교 분석하여 낙동강 하류 일원에서 기러기류의 지역별 개체수 및 분포 특성을 알아보고자 하였다. 조사기간 동안 관찰된 기러기류는 3종 56,790개체였으며, 개리(A. cygnoides), 큰기러기(A. fabalis), 쇠기러기(A. albifrons) 순으로 관찰되었다. 가장 많은 개체수를 나타내는 지역은 대마등으로 기러기류의 분포는 서식지의 존재여부에 큰 영향을 미치고 있으므로 채식지와 휴식지(잠자리포함)의 확보와 보존이 필요하다.