This study analyzed the regional characteristics of extreme drought events in each of the medium-scale basins in the Korean Peninsula by using the Standardized Precipitation Index(SPI), one of the typical drought indexes, and analyzed hydrologic risk by season and basin in consideration of the exceedance probability of all the observational data. According to the results of estimating SPI with the observational rainfall data and analyzing severe droughts' time and space characteristics as well as tendencies, spring droughts are more serious in the Korean Peninsula. In addition, according to the results of analyzing average hydrologic risk by using 4 GCMs for five major rivers' basins in the Korean Peninsula, about short-term mid-term droughts, basin regions weak for droughts are expected to increase in the Korean Peninsula. It is expected that the method for analyzing basins' hydrologic risk in consideration of extreme droughts suggested here in this study will show high applicability in predicting droughts in the Korean Peninsula according to the climatic change and establishing practical coping strategies.
In this study, a quantitative assessment was carried out in order to identify the agricultural drought in time and space using the Terra MODIS remote sensing data for the agricultural drought. The Normalized Difference Vegetation Index (NDVI) and Enhanced Vegetation Index (EVI) were selected by MOD13A3 image which shows the changes in vegetation conditions. The land cover classification was made to show only vegetation excluding water and urbanized areas in order to collect the land information efficiently by Type1 of MCD12Q1 images. NDVI and EVI index calculated using land cover classification indicates the strong seasonal tendency. Therefore, standardized Vegetation Stress Index Anomaly (VSIA) of EVI were used to estimated the medium-scale regions in Korea during the extreme drought year 2001. In addition, the agricultural drought damages were investigated in the country's past, and it was calculated based on the Standardized Precipitation Index (SPI) using the data of the ground stations. The VSIA were compared with SPI based on historical drought in Korea and application for drought assessment was made by temporal and spatial correlation analysis to diagnose the properties of agricultural droughts in Korea.
Using monthly rainfalls, this study investigated outliers of annual and/or seasonal rainfall for quantitative assessment of historical droughts in Korea. Based on the analysis of annual rainfall, Icheon, Geochang, Jeongeup, Suncheon and Jangheung gaging stations were selected to represent the major river basins, because they had most frequent dry years. The overall results indicated that the years of 1988 and 1994 were the worst dry years. Although the 2001 drought was not severe, it resulted in typical agricultural drought damage mainly in Seomjin and Yeongsan river basin due to the lack of agricultural water. On the other hand, the droughts of 1981-1982 and 1994-1995 were long term nation wide droughts that lasted more than two years resulting in extensive drought damages to parts of the country.
In this study, the hydrological drought index was calculated using Modified Water Supply Index (MSWSI). The quantified value corresponding to MSWSI-1 was estimated from the relationship between drought index and input factor. The target area was the 3006 basin where precipitation, river flow, and dam inflow have been recorded for 21 years (January 1997 to August 2017). The drought index was estimated over two time intervals, one month and three months moving average. The quantitative values were estimated for each month and for each input data using a linear regression equation. The monthly MSWSI showed considerable variability between the drought and wet conditions. And also the coefficient of determination between drought index and each input data revealed no correlation. To improve the coefficient of determination and to derive the appropriate linear regression constants, the ranking by each factor and the rank difference between MSWSI drought index and each input factor were calculated. The applied rank difference was estimated to be within 15% and 30%. Re-quantifying the available water resources is expected to be useful in preparing water use policy.
This study aims to investigate droughts from the magnitude perspective based on the SPI (Standardized Precipitation Index) and the theory of runs applicable to quantitative analysis of drought in South Korea. In addition, the dry spell analysis was conducted on the drought history in the five major river basins of South Korea to obtain the magnitude, duration and severity of drought, and the quantitative evaluation has been made on historical droughts by estimating the return period using the SDF(Severity-Duration-Frequency) curve gained through drought frequency analysis. The analysis results showed that the return periods for droughts at the regional and major river basin scales were clearly identified. The return periods of severe drought that occurred around the major river basins in South Korea turn out to be mostly 30 to 50 years with the years of the worst drought in terms of severity being 1988 and 1994. In particular, South Korea experienced extremely severe droughts for two consecutive years during the period between 1994 and 1995. Drought in 2014 occurred in the Han River basin and was evaluated as the worst one in terms of severity and magnitude.
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