• Journal of Korean Society on Water Environment
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• v.37 no.5
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• pp.369-380
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• 2021

In this work, we analyzed the effects of drought on the water temperature (WT) of Nakdong river basin major river sections using Standardized Precipitation Index (SPI) and WT data. The analysis was carried out on a seasonal basis. After calculating the optimal time scale of the SPI through the correlation between the SPI and WT data, we used the copula theory to model the joint probability distribution between the WT and SPI on the optimal time scale. During spring and fall, the possibility of environmental drought caused by high WT increased in most of the river sections. Notably, in summer, the possibility of environmental drought caused by high WT increased in all river sections. On the other hand, in winter, the possibility of environmental drought caused by low WT increased in most river sections. From the risk map, which quantified the sensitivity of WT to the risk of environmental drought, the river sections Nakbon C, Namgang E, and Nakbon K showed increased stress in the water ecosystem due to high WT when drought occurred in summer. When drought occurred in winter, an increased water ecosystem stress caused by falling WT was observed in the river sections Gilan A, Yongjeon A, Nakbon F, Hwanggang B, Nakbon I, Nakbon J, Nakbon K, Nakbon L, and Nakbon M. The methodology developed in this study will be used in the future to quantify the effects of drought on water quality as well as WT.

• Journal of The Korean Society of Agricultural Engineers
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• v.57 no.1
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• pp.59-67
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• 2015

Because reservoirs that supply irrigation water play an important role in water resource management, it is necessary to evaluate the vulnerability of this particular water supply resource. The purpose of this study is to provide water supply risk maps of agricultural reservoirs in South Korea using irrigation vulnerability model and cluster analysis. To quantify water supply risk, irrigation vulnerability indices are estimated to evaluate the performance of the water supply on the agricultural reservoir system using a probability theory and reliability analysis. First, the irrigation vulnerability probabilities of 1,346 reservoirs managed by Korea Rural Community Corporation (KRC) were analyzed using meteorological data on 54 meteorological stations over the past 30 years (1981-2010). Second, using the K-mean method of non-hierarchical cluster analysis and pre-simulation approach, cluster analysis was applied to classify into three groups for characterizing irrigation vulnerability in reservoirs. The morphology index, watershed area, irrigated area, and ratio between watershed and irrigated area are selected as the clustering analysis parameters. It is suggested that the water supply risk map be utilized as a basis for the establishment of risk management measures, and could provide effective information for a reasonable decision making on drought risk mitigation.

• Journal of Korea Water Resources Association
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• v.54 no.9
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• pp.705-718
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• 2021

Climate change has a significant impact on vegetation growth and terrestrial ecosystems. In this study, the possibility of ecological drought was investigated using satellite remote sensing data. First, the Vegetation Health Index was estimated from the Normalized Difference Vegetation Index and Land Surface Temperature provided by MODIS. Then, a joint probability model was constructed to estimate the possibility of vegetation-related drought in various precipitation/evaporation scenarios in forest areas around 60 major ASOS sites of the Meteorological Administration located throughout Korea. The results of this study show the risk pattern of drought related to forest vegetation under conditions of low atmospheric moisture supply or high atmospheric moisture demand. It also identifies the sensitivity of drought risks associated with forest vegetation under various meterological drought conditions. These findings provide insights for decision makers to assess drought risk and develop drought mitigation strategies related to forest vegetation in a warming era.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.6B
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• pp.561-569
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• 2010

In this study, the impact of climate change on extreme drought events is investigated by comparing drought severity-area-duration curves under present and future climate. The depth-area-duration analysis for characterizing an extreme precipitation event provides a basis for analysing drought events when storm depth is replaced by an appropriate measure of drought severity. In our climate-change impact experiments, the future monthly precipitation time series is based on a KMA regional climate model which has a $27km{\times}27km$ spatial resolution, and the drought severity is computed using the standardized precipitation index. As a result, agricultural drought risk is likely to increase especially in short duration, while hydrologic drought risk will greatly increase in all durations. Such results indicate that a climate change vulnerability assessment for present water resources supply system is urgent.

• Journal of Environmental Science International
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• v.29 no.11
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• pp.1099-1108
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• 2020

In this study, the capacity of supplying agricultural water to 13 districts was analyzed by calculating the necessary water supply for the arable land of Gunwi-gun and examining the capacity of supplying water to reservoirs, streams, pumping stations, collection sites, and groundwater wells in Gunwi-gun. As a result, among the 13 districts the second district was found to be short of water by 1.2×10⁶ tons/year. In general, local governments establish drought measures by selecting drought disaster risk zones. While selecting drought-risk areas, some water-poor areas that do not have water sources should be selected, even if the entire area has a sufficient water supply. The water-supply evaluation at the regional level was insufficient for locating areas without water sources, but most areas with water sources, such as streams, reservoirs, and pumping stations, were found to have no shortage of water. To locate water shortage areas without water sources, GIS analysis conducted a field survey of areas with a distance of 4 or less than that of water sources analyzed by GIS analysis. Sixty-nine sites in 13 districts were selected for the on-site survey and six areas of water shortage were identified in areas other than the second district.

• Journal of Korea Water Resources Association
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• v.56 no.2
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• pp.151-163
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• 2023

This study explored the 2022 drought over the Nakdong River watershed. Here, we developed a bivariate regional frequency analysis method to evaluate the risk of hydrological drought. Currently, natural streamflow data are generally limited to accurately estimating the drought frequency. Under this circumstance, the existing at site frequency analysis can be problematic in estimating the drought risk. On the other hand, a regional frequency analysis could provide a more reliable estimation of the joint return periods of drought variables by pooling available streamflow data over the entire watershed. More specifically, the Copula-based regional frequency analysis model was proposed to effectively take into account the tail dependencies between drought variables. The results confirmed that the regional frequency analysis model showed better performance in model fit by comparing the goodness-of-fit measures with the at-site frequency analysis model. We find that the estimated joint return period of the 2022 drought in the Nakdong River basin is about eight years. In the case of the Nam river Dam, the joint return period was approximately 20 years, which can be regarded as a relatively severe drought over the last three decades.

• Journal of Korea Water Resources Association
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• v.56 no.8
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• pp.485-496
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• 2023

Recently, South Korea has been making efforts to mitigate the risk of water scarcity during droughts by utilizing various drought response measures in dam operations. While various studies have been conducted on this topic, there is currently a lack of research on the economic effects of drought response measures. In this study, we evaluated the economic effects of drought response measures on nationwide multipurpose dams by using a long-term simulated inflow model based on ARIMA and Copula and a dam operation model that reflects drought response measures. The results showed that the expected benefits per unit flow rate were highest for coordinated operation and alternative water supply measures, at KRW 1,176 and KRW 1,139, respectively, while the benefits of emergency water supply utilization and water supply adjustment were estimated at KRW 956 and KRW 875, respectively. Additionally, when we examined the changes in the economic benefits of drought response measures based on the assumption of increased drought severity in the future, the changes in the drought risk resulting from reduced inflow increased the economic benefits of all drought response measures. The economic benefits of water supply adjustment increased by 2.6% compared to the baseline, while the economic benefits of coordinated operation and alternative water supply measures increased by 11.7% compared to the baseline. This suggests that dam-network-based measures, such as coordinated operation and alternative water supply measures, are crucial as drought risk increases. This study is expected to serve as a fundamental reference for selecting and utilizing drought response measures in the future.

• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.150-150
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• 2019

The development of prolong and severe drought can directly impact on the environment, agriculture, economics and society of country. A lot of efforts have been made across worldwide in the planning, monitoring and mitigation of drought. Currently, different drought indices such as the Palmer Drought Severity Index (PDSI), Standardized Precipitation Index (SPI), Standardized Precipitation Evapotranspiration Index (SPEI) are developed and most commonly used to monitor drought characteristics quantitatively. However, it will be very meaningful and essential to develop a more effective technique for assessment and monitoring of onset and end of drought. Therefore, in this study, the hidden Markov Bayesian classifier (MBC) was employed for the assessment of onset and end of meteorological drought classes. The results showed that the probabilities of different classes based on the MBC were quite suitable and can be employed to estimate onset and end of each class for meteorological droughts. The classification results of MBC were compared with SPI and with past studies which proved that the MBC was able to account accuracy in determining the accurate drought classes. For more performance evaluation of classification results confusion matrix was used to find accuracy and precision in predicting the classes and their results are also appropriate. The overall results indicate that the MBC was effective in predicating the onset and end of drought events and can utilized for monitoring and management of short-term drought risk.

• Journal of Korea Water Resources Association
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• v.46 no.4
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• pp.425-437
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• 2013

This study performed the bivariate drought frequency analysis for duration and severity of drought, using copula functions which allow considering the correlation structure of joint features of drought. We suggested the confidence intervals of duration-severity-frequency (DSF) curves for the given drought duration using stochastic scheme of monthly rainfall generation for 57 sites in Korea. This study also investigated drought risk via illustrating the largest drought events on record over 50 and 100 consecutive years. It appears that drought risks are much higher in some parts of the Nakdong River basin, southern and east coastal areas. However, such analyses are not always reliable, especially when the frequency analysis is performed based on the data observed over relatively short period of time. To quantify the uncertainty of drought frequency curves, the droughts were filtered by different durations. The 5%, 25%, 50%, 75%, and 95% confidence intervals of the drought severity for a given duration were estimated based on the simulated rainfall time series. Finally, it is shown that the growing uncertainties is revealed in the estimation of the joint probability using the two marginal distributions since the correlation coefficient of two variables is relatively low.

• Journal of Korea Water Resources Association
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• v.51 no.spc
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• pp.1117-1126
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• 2018

Water supply system aims to meet the user's demand by securing water resources in a stable way. However, water supply failure sometimes happens because inflow decreases during drought period. Droughts induced by the lack of precipitation do not always lead to water supply failures. Thus, it is necessary to consider features of actual water shortage event when we evaluate a water supply risk. In this study, we developed a new drought index for drought management, i.e., Joint Drought Management Index (JDMI), using two water supply system performance indices such as reliability and vulnerability. Future data that were estimated from GCMs according to RCP 4.5 and 8.5 scenarios were used to estimate future water supply risk. After dividing the future period into three parts, the risk of water supply failure in the Nakdong River basin was analyzed using the JDMI. As a result, the risk was higher with the RCP 4.5 than the RCP 8.5. In case of RCP 4.5, W18 (Namgangdam) was identified as the most vulnerable area, whereas in case of RCP 8.5, W23 (Hyeongsangang) and W33 (Nakdonggangnamhae) were identified as the most vulnerable area.