• Journal of Korea Water Resources Association
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• v.52 no.8
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• pp.545-554
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• 2019

The most drought assessments are based on a drought index, which depends on univariate variables such as precipitation and soil moisture. However, there is a limitation in representing the drought conditions with single variables due to their complexity. It has been acknowledged that a multivariate drought index can more effectively describe the complex drought state. In this context, this study propose a Copula-based drought index that can jointly consider precipitation and soil moisture. Unlike precipitation data, long-term soil moisture data is not readily available so that this study utilized a Gaussian Mixture Non-Homogeneous Hidden Markov chain Model (GM-NHMM) model to simulate the soil moisture using the observed precipitation and temperature ranging from 1973 to 2014. The GM-NHMM model showed a better performance in terms of reproducing key statistics of soil moisture, compared to a multiple regression model. Finally, a bivariate frequency analysis was performed for the drought duration and severity, and it was confirmed that the recent droughts over Jeollabuk-do in 2015 have a 20-year return period.

• Journal of The Korean Society of Agricultural Engineers
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• v.63 no.5
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• pp.1-11
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• 2021

Soil moisture plays a critical role in hydrological processes, land-atmosphere interactions and climate variability. It can limit vegetation growth as well as infiltration of rainfall and therefore very important for agriculture sector and food protection. Recently, due to the increased damage from drought caused by climate change, there is a frequent occurrence of shortage of agricultural water, making it difficult to supply and manage stable agricultural water. Efficient water management is necessary to reduce drought damage, and soil moisture management is important in case of upland crops. In this study, soil moisture was calculated based on the water balance model, and the suitability of soil moisture data was verified through the application. The regional soil moisture was calculated based on the meteorological data collected by the meteorological station, and applied the Runs theory. We analyzed the spatiotemporal variability of soil moisture and drought impacts, and analyzed the correlation between actual drought impacts and drought damage through correlation analysis of Standardized Precipitation Index (SPI). The soil moisture steadily decreased and increased until the rainy season, while the drought size steadily increased and decreased until the rainy season. The regional magnitude of the drought was large in Gyeonggi-do and Gyeongsang-do, and in winter, severe drought occurred in areas of Gangwon-do. As a result of comparative analysis with actual drought events, it was confirmed that there is a high correlation with SPI by each time scale drought events with a correlation coefficient.

• Atmosphere
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• v.18 no.4
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• pp.249-266
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• 2008

The tendencies for teleconnection with a time lag and other characteristics of Korean summer droughts have been investigated and some clues to predict the drought occurrences several months before have been found. First, the May and June droughts in Korea are simultaneous with those over the northwestern part of Korea owing to the relation with the baroclinic wave. However, the July and August droughts occur over the mid-latitudes or southern part of Korea owing to the relation with the Changma front. Second, several months before the MJJA droughts in Korea, it is found that the effective drought index (EDI) over particular areas (hereafter, referred to as the omen areas) is large. Thailand, Carolina Island, Mongolia, and Central Bengal Bay were selected as the omen areas. Third, when the monthly minimum EDI (MME) of the omen area in winter is more than 0.7, it signifies that the precipitation is above normal, Korea has almost always experienced a summer drought. However, the droughts occurring with this type of relationship only represent half of the MJJA droughts in Korea. Fourth, the relationships between the Korean drought and the precipitation over omen areas in low latitudes are not valid over all the eight precipitation areas in Korea, but only over Areas I, II, and III, where heavy rains occur during spring and summer.

• Proceedings of the Korea Water Resources Association Conference
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• 2018.05a
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• pp.22-22
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• 2018

본 연구에서는 수문학적 가뭄을 분석하기 위해 두가지 지수를 개발하여 소개하고자 한다. 첫번째는, 물수지식을 기반으로 산정된 Water Budget-based Drought Index(WBDI)로 강우와 증발산의 차이를 이용하여 산정한다. 두 번째는 에너지 수지식을 기반으로 산정된 Energy-based Water Deficit Index(EWDI)로 에너지 수지 기반의 증발산, 태양복사에너지와 토양수분 등을 이용하여 산정한다. 두가지 지수 모두 인공위성 영상 자료를 활용하였다. WBDI 산정을 위한 강수량 자료는 Tropical Rainfall Measuring Mission(TRMM)과 Global Precipitation Mission(GPM)를 활용하였으며, 증발산 자료는 Moderate Resolution Imaging Spectroradiometer (MODIS) 자료를 활용하였다. EWDI 산정에 필요한 입력자료는 모두 MODIS 자료를 활용하였다. 산정된 두 가뭄지수의 수문학적 가뭄 분석을 위해 자연유출지점인 6개 지점을 선정하여 유출량 자료와 비교하였다. 유출량 자료를 활용하여 Error matrix 기법을 적용하여 두 수문학적 가뭄지수의 우리나라에서의 적용성을 파악하였다.

• Journal of Korea Water Resources Association
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• v.45 no.10
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• pp.983-995
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• 2012

In this study, it was intended to analyze the spatio-temporal distribution of historical drought events occurred in Korea by way of drought frequency analysis using SPI (Standardized Precipitation Index), and Drought spell was executed to estimate drought frequency as per drought severity and regions. Also, SDF (severity-duration-frequency) curves were prepared per each weather stations to estimate spatial distribution characteristics for the severe drought areas of Korea, and Potential Drought Hazard Map was prepared based on the derived SDF curves. Drought frequency analysis per drought stage revealed that severe drought as well as extreme drought frequency were prominently high at Geum River, Nakdong River, and Seomjin River basin as can be seen from SDF curves, and drought severity was found as severer per each drought return period in the data located at Geum River, Nakdong River, and Seomjin River basins as compared with that of Seoul weather station at Han River basin. In the Potential Drought Hazard Map, it showed that Geum River, Seomjin River, and Yeongsan River basins were drought vulnerable areas as compared to upper streams of Nakdong River basin and Han River basin, and showed similar result in drought frequency per drought stage. Drought was occurred frequently during spring seasons with tendency of frequent short drought spell as indicated in Potential Drought Hazard Map of different season.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.40 no.1
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• pp.25-33
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• 2020

A drought event is characterized by duration, severity and affected area. In general, after calculating a drought index using hydro-meteorological time series at a station, a drought event is defined based on the run theory to identify the beginning and end time. However, this one-dimensional analysis has limitations for analyzing the spatio-temporal occurrence characteristics and movement paths of drought. Therefore, this study is to define a three-dimensional drought event using a simple clustering algorithm and to develop a drought map that can be used to understand the drought severity according to the spatio-temporal expansion of drought. As a result, compared with the two-dimensional monitoring information to show spatial distribution of drought index, a proposed drought map is able to show three-dimensional drought characteristics inclusing drought duration, spatial cumulative severity, and centroid of drought. The analysis of drought map indicated that there was a drought event which had the affected area less than 10 % while on occations while there were 11 drought events (44 %) which had the affected area more a than 90 % of the total area. This means that it is important to understand the relationship between spatial variation of drought affected area and severity corresponding to various drought durations. The development of drought map based on three-dimensional drought analysis is useful to analyze the spatio-temporal occurrence characteristics and propagation patterns of regional drought which can be utilized in developing mitigation measures for future extreme droughts.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.3B
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• pp.185-192
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• 2012

Drought vulnerability index was developed by selecting drought-related indicators with trend test. Study areas were determined by considering the weir locations from the four major rivers restoration project in Nakdong and Geum river watersheds. Ten indicators were selected and they were categorized into three groups, water resources, precipitation pattern, and social aspects. Annual average surface water level, annual minimum surface water level, annual average groundwater level, and annual minimum groundwater level data sets were collected for water resources aspects. The number of non-rainy days, rainfall concentration ratio, and rainfall deviation were considered for precipitation pattern category. The amount of water available per capita, financial soundness for water resources, and water usage equity were related to social aspects. Mann-Kendall, Hotelling-Pabst, and Sen trend tests were performed for the ten indicator data sets and the results were scored for the drought vulnerability index. The results shows Gumi, Sangjoo, and Hapcheon weirs are relatively vulnerable to drought. The indices were relatively low for the regions in Geum river watershed compared to those in Nakdong river watershed.

• Journal of The Korean Society of Agricultural Engineers
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• v.61 no.2
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• pp.1-11
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• 2019

Remote sensing products have long been used to monitor and forecast natural disasters. Satellite-derived rainfall products are becoming more accurate as space and time resolution improve, and are widely used in areas where measurement is difficult because of the periodic accumulation of images in large areas. In the case of North Korea, there is a limit to the estimation of precipitation for unmeasured areas due to the limited accessibility and quality of statistical data. CHIRPS (Climate Hazards Group InfraRed Precipitation with Stations) is global satellite-derived rainfall data of 0.05 degree grid resolution. It has been available since 1981 from USAID (U.S. Agency for International Development), NASA (National Aeronautics and Space Administration), NOAA (National Oceanic and Atmospheric Administration). This study evaluates the applicability of CHIRPS rainfall products for South Korea and North Korea by comparing CHIRPS data with ground observation data, and analyzing temporal and spatial drought trends using the Standardized Precipitation Index (SPI), a meteorological drought index available through CHIRPS. The results indicate that the data set performed well in assessing drought years (1994, 2000, 2015 and 2017). Overall, this study concludes that CHIRPS is a valuable tool for using data to estimate precipitation and drought monitoring in Korea.

• Atmosphere
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• v.19 no.1
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• pp.67-78
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• 2009

A strong negative correlation has been detected between the North Pacific Oscillation Index (NPI) and the Effective Drought Index (EDI) in May over Korea. In May of positive NPI year, anomalous patterns caused a drought in Korea as follows: the anomalous south-low, north-high low-level pressure patterns in the northeast and southeast of Korea have strengthened the anomalous northerlies to Korea. In addition, these anomalous northerlies have prevented western North Pacific (WNP) high from moving northward. As a result, anomalous descending flows have strengthened in the mid-latitude region in East Asia. In the WNP, the anomalous south-high, north-low sea surface temperature (SST) has been widely distributed, which has strengthened anomalous south-low, north-high low-level pressure patterns. These anomalous characteristics of pressure and SST patterns observed in May of positive NPI years have already been detected in previous winter (December-February) and early spring (March, April). In addition, the anomalous negative sea ice concentration in the North Pacific during two seasons has strengthened the anomalous anticyclonic circulation in the same region and in turn made a contribution to formation of anomalous south-low, north-high pressure patterns in May.

• Environmental Engineering Research
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• v.21 no.1
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• pp.58-68
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• 2016

The study explored droughts using the Standardized Precipitation Index (SPI) in the northwestern region of Bangladesh, which is the drought prone area. In order to assess the trend and variability of monthly rainfall, as well as 3-month scale SPI, non-parametric Mann-Kendall (MK) tests and continuous wavelet transform were used respectively. The effect of climatic parameters on the drought in this region was also evaluated using SPI, with the Southern Oscilation Index (SOI) by means of the wavelet coherence technique, a relatively new and powerful tool for describing processes. The MK test showed no statistically significant monthly rainfall trends in the selected stations, whereas the seasonal MK test showed a declining rainfall trend in Bogra, Ishurdi, Rangpur and Sayedpur stations respectively. Sen's slope of six stations also provided a decreasing rainfall trend. The trend of the SPI, as well as Sen's slope indicated an increasing dryness trend in this area. Dominant periodicity of 3-month scale SPI at 8 to 16 months, 16 to 32 months, and 32 to 64 months were observed in the study area. The outcomes from this study contribute to hydrologists to establish strategies, priorities and proper use of water resources.