• Journal of Wetlands Research
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• v.21 no.spc
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• pp.80-89
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• 2019

The purpose of this study is to analyze the relationship between SPI (Standardized Precipitation Index) meteorological drought and RDI (Reservoir Drought Index) agricultural drought for Geum river basin. Drought Indices was calculated by collecting data of precipitation and agricultural reservoir water storage rate from 2014 to 2016. To evaluated the correlation between meteorological and agricultural drought, the Pearson correlation and the Receiver Operation Characteristic (ROC) analysis were conducted to evaluate the correlation between meteorological and agricultural droughts. The SPI-6 and RDI showed the highest relationship with Pearson coefficient 0.606 and ROC hit rates 0.722 respectively, and the spatial occurrence patterns of drought using overlapped SPI-6 and RDI, the big differences between the 2 indices were occurred in the upstream areas of Miho stream and Nonsan stream from August to October 2015. The analysis using reservoirs specifications for areas where reservoir droughts occurred was conducted, and the areas showing severe drought of RDI were the reservoir areas having relatively small value of basin magnifying power (BMP). This means that a reservoir has the reaction capability for agricultural drought mainly depending on the reservoir BMP.

• Journal of Korea Water Resources Association
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• v.44 no.8
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• pp.667-681
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• 2011

The objective of this study is to evaluate the applicability of a Land Surface Model (LSM) for drought analysis in Korea. For evaluating the applicability of the model, the model was calibrated on several upper dam site watersheds and the hydrological components (runoff and soil moisture) were simulated over the whole South Korea at grid basis. After converting daily series of runoff and soil moisture data to accumulated time series (3, 6, 12 months), drought indices such as SRI and SSI are calculated through frequency analysis and standardization of accumulated probability. For evaluating the drought indices, past drought events are investigated and drought indices including SPI and PDSI are used for comparative analysis. Temporal and spatial analysis of the drought indices in addition to hydrologic component analysis are performed to evaluate the reproducibility of drought severity as well as relieving of drought. It can be concluded that the proposed indices obtained from the LSM model show good performance to reflect the historical drought events for both spatially and temporally. From this point of view, the LSM can be useful for drought management. It leads to the conclusion that these indices are applicable to domestic drought and water management.

• Journal of Korea Water Resources Association
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• v.50 no.10
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• pp.691-701
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• 2017

The objective of this study is to evaluate the long-term drought outlook information based on long-term forecast data for the 2015 drought event. In order to estimate the Standardized Precipitation Index (SPI) for different durations (3-, 6-, 9-, 12-months), we used the observation precipitation of 59 Automated Synoptic Observing System (ASOS) sites, forecast and hindcast data of GloSea5. The Receiver Operating Characteristic (ROC) analysis and statistical analysis (Correlation Coefficient, CC; Root Mean Square Error, RMSE) were used to evaluate the utilization of drought outlook information for the forecast lead-times (1~6months). As a result of ROC analysis, ROC scores of SPI(3), SPI(6), SPI(9) and SPI(12) were estimated to be over 0.70 until the 2-, 3-, 4- and 5-months. The CC and RMSE values of SPI(3), SPI(6), SPI(9) and SPI(12) for forecast lead-time were estimated as (0.60, 0.87), (0.72, 0.95), (0.75, 0.95) and (0.77, 0.89) until the 2-, 4-, 5- and 6-months respectively.

• Journal of Korea Water Resources Association
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• v.32 no.2
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• pp.197-210
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• 1999

This study examines the duration and severity of droughts by the use of stochastic process considerations. The key annual flow statistics are used to estimate the related statistics of drought probability distributions for various combinations of return period and water demand. This study efforts initially focused on analyzing all the nation streamgage records that were judged to meet certain selection criteria, including those of record length, record quality. These analyses resulted in the determination of those annual flow statistics necessary to define the behavior of drought sequences for the selected streams. Using prior research results, the actual or estimated flow statistics are related to the probability distributions of maximum drought events, through the application of the theory of runs. This has resulted in assigning return periods to drought events at gaged locations, and permits an assessment of the probabilities of observed historical drought within the nation.

• The Journal of Engineering Geology
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• v.29 no.4
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• pp.469-481
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• 2019

In addition to structural stabilization measures such as the construction of Sand Dam, non-structural management measures such as reasonable water demand and supply volume management are needed to prevent limited water supply damage due to drought. In this study, water supply-demand monitoring system was established for drought response in Seosang-ri basin in Chuncheon, the main source of domestic water for small water facilities. The flow rate of the stream was measured for monitoring the supply volume, and the daily flow rate was calculated by using it to calibrate the parameters of the SWAT (Soil and Water Assessment Tool). To monitor demand, the daily usage was calculated by measuring the change in the water level of the water tank. The relationship between the finally calculated daily supply and demand amount was analyzed to identify the shortage of water.

• Journal of The Korean Society of Agricultural Engineers
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• v.62 no.2
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• pp.111-120
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• 2020

This study assessed the reliability of the agricultural water supply based on future climate change scenarios, and suggested plans to improve the reliability in order to promote the adaptability of irrigation water in agricultural reservoirs to climate change. The assessment of agricultural water supply reliability was performed on reservoirs which had a lower water quantity than their design basis and which had recently been subject to drought. In other words, from the irrigation districts of main intake works among the reservoirs managed by the Korea Rural Community Corporation, 1~2 districts in each province-that is, a total of 13 districts -that were recently designated as a district for securing agricultural water (drought prevention district) were selected. Climate change scenarios were applied to the selected districts to analyze their future water supply reliability compared to the current level. All districts selected showed a drought frequency of 4 years or shorter, which demonstrated the need to establish climate change response plans. As plans for responding to climate change, a plan that utilizes supplemental intake works to reduce the area of the irrigation districts of main intake works, and another one that increases the capacity of main intake works were adopted to reanalyze their water supply reliability. When the area of the irrigation districts of main intake works was reduced by about 30~40%, the drought frequency dropped to more than 10 years, securing the reliability of water supply. To secure the reliability by increasing the capacity of main intake works, it was calculated that about 19,000~2,400,000 tons need to be added to each reservoir. In addition, climate change response plans were suggested to improve the reliability of the water supply in each district based on the results of economic analysis.

• Journal of The Korean Society of Agricultural Engineers
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• v.62 no.6
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• pp.73-83
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• 2020

Agricultural drought is a natural phenomenon that is difficult to observe and quantitatively express, and agricultural water use is high and usage patterns are diverse, so even if there is a lack of rainfall. The frequency and severity of agricultural drought are increased during the irrigation period where the demand for agricultural water is generated, and reasonable and efficient management of agricultural water for stable water supply is required. As one method to solve the water shortage of agricultural water in an unstructured method, it is necessary to analyze the appropriate supply amount and supply method through simulation from the intake works to the canals organization and paddy field. In this study, irrigation efficiency was analyzed for irrigation systems from April to September over the past three years from the Musu Reservoir located in Jincheon-gun, Chungcheongbuk-do and Pungjeon Reservoir located in Seosan-si, Chungcheongnam-do. SWMM (Storm Water Management Model) was used to collect agricultural water, and irrigation efficiency analysis was conducted using adequacy indicators, and water supply vulnerability. The results of the agricultural water distribution simulation, irrigation efficiency and water supply vulnerability assessment are thought to help the overall understanding of the agricultural water supply and the efficient water management through preliminary analysis of the methods of agricultural water supply in case of drought events.

• Journal of Korea Water Resources Association
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• v.49 no.6
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• pp.565-577
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• 2016

The objective of this study is to propose a method for computing the Natural Drought Index (NDI) that does not consider man-made drought facilities. Principal Component Analysis (PCA) was used to estimate the NDI. Three monthly moving cumulative runoff, soil moisture and precipitation were selected as input data of the NDI during 1977~2012. Observed precipitation data was collected from KMA ASOS (Korea Meteorological Association Automatic Synoptic Observation System), while model-driven runoff and soil moisture from Variable Infiltration Capacity Model (VIC Model) were used. Time series analysis, drought characteristic analysis and spatial analysis were used to assess the utilization of NDI and compare with existing SPI, SRI and SSI. The NDI precisely reflected onset and termination of past drought events with mean absolute error of 0.85 in time series analysis. It explained well duration and inter-arrival time with 1.3 and 1.0 respectively in drought characteristic analysis. Also, the NDI reflected regional drought condition well in spatial analysis. The accuracy rank of drought onset, termination, duration and inter-arrival time was calculated by using NDI, SPI, SRI and SSI. The result showed that NDI is more precise than the others. The NDI overcomes the limitation of univariate drought indices and can be useful for drought analysis as representative measure of different types of drought such as meteorological, hydrological and agricultural droughts.

• Journal of Korea Water Resources Association
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• v.54 no.10
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• pp.769-777
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• 2021

This study investigated the change of the achievement rate of the target water quality conditioned on the occurrence of severe drought, to assess the effects of meteorological drought on the water quality management in the Nakdong River basin. Using three drought indices with difference time scales such as 30-, 60-, 90-day, i.e., SPI30, SPI60, SPI90, and three water quality indicators such as biochemical oxygen demand (BOD), total organic carbon (TOC), and total phosphorus (T-P), we first analyzed the relationship between severe drought occurrence water quality change in mid-sized watersheds, and identified the watersheds in which water quality was highly affected by severe drought. The Bayesian network models were constructed for the watersheds to probabilistically assess the relationship between severe drought and water quality management. Among 22 mid-sized watersheds in the Nakdong River basin, four watersheds, such as #2005, #2018, #2021, and #2022, had high environmental vulnerability to severe drought. In addition, severe drought affected spring and fall water quality in the watershed #2021, summer water quality in the #2005, and winter water quality in the #2022. The causal relationship between drought and water quality management is usufaul in proactive drought management.

• 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.