• Journal of Environmental Science International
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• v.25 no.11
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• pp.1511-1519
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• 2016

Jeju Island relies on subterranean water for over 98% of its water resources, and it is therefore necessary to continue to perform studies on drought due to climate changes. In this study, the representative standardized precipitation index (SPI) is classified by various criteria, and the spatial characteristics and applicability of drought in Jeju Island are evaluated from the results. As the result of calculating SPI of 4 weather stations (SPI 3, 6, 9, 12), SPI 12 was found to be relatively simple compared to SPI 6. Also, it was verified that the fluctuation of SPI was greater fot short-term data, and that long-term data was relatively more useful for judging extreme drought. Cluster analysis was performed using the K-means technique, with two variables extracted as the result of factor analysis, and the clustering was terminated with seven-time repeated calculations, and eventually two clusters were formed.

• Journal of The Korean Society of Agricultural Engineers
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• v.65 no.5
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• pp.37-49
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• 2023

The drought risk has been increasing recently due to climate change causing the extreme climate to be more frequent. In order to supply agricultural water stably under drought, it is necessary to operate an agricultural reservoir in response to drought. To this end, it is crucial to establish appropriate drought response operation rules considering weather conditions and reservoir status. In the reservoir operation simulation, the supply amount differs from the actual reservoir supply for many reasons, including maintaining water levels for supply and accommodating farmers' requests. So, for a more realistic reservoir operation simulation, it is necessary to reflect the reservoir operation rules of the actual water management site. Therefore, in this study, through a survey, the standards for limitation of agricultural water supply applied to agricultural reservoirs in Korea were investigated, and the criteria for drought response reservoir operation (DRO) were established based on the survey. Then, the DRO was applied to the irrigation period for nine subject reservoirs. The applicability was evaluated by comparing the DRO result to the operation result of HOMWRS (Hydrological Operation Model for Water Resources System). The reservoir drought index, storage rate, and daily supply were compared for evaluation. From the result, DRO showed more stable operation results in most cases against drought as it has fewer days of water supply limitation and a somewhat reservoir storage rate which can be utilized for prolonged drought.

• Journal of Korea Water Resources Association
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• v.57 no.1
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• pp.45-58
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• 2024

Drought risk is expected to increase as the frequency, intensity, and duration of droughts increase due to climate change. Drought risk is related to not only hydro-meteorological factors, but also water supply and demand. Recently, along with climate change, socioeconomic factors have also been recognized to increase drought risk. Therefore, it is necessary to outlook the drought risk considering various conditions for coping with future extreme droughts in a timely manner. In addition, considering various drought scenarios help reduce the uncertainty in future drought outlook. In this study, drought scenarios considering climate change scenarios, population, and water demand were created to outlook drought risk for 160 administrative districts in Korea, then new levels of drought risk were assigned based on the results of drought risk outlook to suggest drought management measures. The results showed that the drought risk will increase in the future in 2020, 2025, and 2030, compared to past. Especially the drought risk is likely twice as high in 2030 under the baseline and high scenarios. Applying the drought outlook results from this study to the new methodology for setting the risk levels shows that most regions are in Response (V) in 2020 and 2030 for baseline and high scenarios.

• Journal of The Korean Society of Agricultural Engineers
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• v.57 no.3
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• pp.65-76
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• 2015

Estimating water requirements for upland crops are characterized by standing soil moisture condition during the entire crop growth period. However, scarce rainfall and intermittent dry spells often cause soil moisture depletion resulting in unsaturated condition in the fields. Changes in rainfall patterns due to climate change have significant influence on the increasing the occurrence of extreme soil moisture depletion. Therefore, it is necessary to evaluate agricultural drought for upland crop water planning and management in the context of climate change. The objective of this study is to predict the impacts of climate change on agricultural drought for upland crops and changes in the temporal trends of drought characteristics. First, the changes in crop evapotranspiration and soil moisture in the six upland crops, such as Soybeans, Maize, Potatoes, Red Peppers, Chinese Cabbage (spring and fall) were analyzed by applying the soil moisture model from commonly available crop and soil characteristics and climate data, and were analyzed for the past 30 years (1981-2010), and Representative Concentration Pathways (RCP) climate change scenarios (2011-2100). Second, the changes on the temporal trends of drought characteristics were performed using run theory, which was used to compare drought duration, severity, and magnitude to allow for quantitative evaluations under past and future climate conditions.

• Journal of Korea Water Resources Association
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• v.47 no.5
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• pp.491-500
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• 2014

To estimate the severity of streamflow drought, this study introduced the concept of streamflow drought index based on threshold level method and Seomjingang Dam inflow was applied. Threshold levels used in this study are fixed, monthly and daily threshold, The $1^{st}{\sim}3^{rd}$ analysis results of annual drought, the severe hydrological droughts were occurred in 1984, 1988 and 1995 and the drought lasted for a long time. Annual compared to extreme values of total water deficit and duration, the drought occurred in 1984, 1988, 1995 and 2001 was serious level. In the results of study, because a fixed threshold level is not reflect seasonal variability, at least the threshold under seasonal level was required. Threshold levels determined by the monthly and daily were appropriate. The proposed methodology in this study can be used to forecast low-flow and determine reservoirs capacity.

• Journal of Environmental Science International
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• v.23 no.4
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• pp.637-647
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• 2014

Quantitative assessment of groundwater level change under extreme event is important since groundwater system is directly affected by drought. Substantially, groundwater level fluctuation reveals to be delayed from several hours to few months after raining according to the aquifer characteristics. Groundwater system in Jeju Island would be also affected by drought and almost all regions were suffered from a severe drought during summer season (July to September) in 2013. To estimate the effect of precipitation to groundwater system, monthly mean groundwater levels in 2013 compared to those in the past from 48 monitoring wells belong to be largely affected by rainfall(Dr) over Jeju Island were analyzed. Mean groundwater levels during summer season recorded 100 mm lowered of precipitation compared to the past 30 years became decreased to range from 2.63 m to 5.42 m in southern region compared to the past and continued to December. These decreasing trends are also found in western(from -1.21 m to -4.06 m), eastern(-0.91 m to -3.24 m), and northern region(from 0.58 m to -4.02 m), respectively. Moreover, the response of groundwater level from drought turned out to be -3.80 m in August after delaying about one month. Therefore, severe drought in 2013 played an important role on groundwater system in Jeju Island and the effect of drought for groundwater level fluctuation was higher in southern region than other ones according to the regional difference of precipitation decrease.

• Journal of Korea Water Resources Association
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• v.56 no.1
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• pp.11-21
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• 2023

This study suggests the drought resilience index as S-day as a means of preparing for the recent extreme drought, allowing for the actual operational identification of each drought countermeasure's priority as well as the vulnerability of water resource facilities to drought. Although each dam's drought measures are unique in this case, the representative examples include adjusting the water supply, linking the functioning of various facilities, and considering emergency capacity. Here, 15 multipurpose dams and water supply dams in Korea were inspected. Under the return period of 20-year drought, most of dams showed stable by adjusting the water supply overall. The measures, however, did not seem to be able to resist a multi-year drought lasting more than two years. Besides, Hoengseong and Anodong-Imha Dam only lasted a year under the 100-year drought return period with other measures. Without the deployment of drought mitigation strategies, it is expected that the Hoengseong Dam, Andong-Imha Dam, Gunwi Dam, Unmun Dam, Daecheong Dam, and Juam Dam would not be able to meet the all water demand for a year under the 20-year drought condition. The ideal capacity for each drought measure was then suggested. Additionally, by increasing or decreasing the current supply contract by 10% in order to account for demand changes resulting from socio-economic instability, the drought response capacity of all 15 dams was re-evaluated. By lowering the supply contract amount by 10%, it was possible to endure a severe drought.

• Journal of Astronomy and Space Sciences
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• v.30 no.4
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• pp.241-246
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• 2013

We have investigated drought periodicities occurred in Seoul to find out any indication of relationship between drought in Korea and solar activities. It is motivated, in view of solar-terrestrial connection, to search for an example of extreme weather condition controlled by solar activity. The periodicity of drought in Seoul has been re-examined using the wavelet transform technique as the consensus is not achieved yet. The reason we have chosen Seoul is because daily precipitation was recorded for longer than 200 years, which meets our requirement that analyses of drought frequency demand long-term historical data to ensure reliable estimates. We have examined three types of time series of the Effective Drought Index (EDI). We have directly analyzed EDI time series in the first place. And we have constructed and analyzed time series of histogram in which the number of days whose EDI is less than -1.5 for a given month of the year is given as a function of time, and one in which the number of occasions where EDI values of three consecutive days are all less than -1.5 is given as a function of time. All the time series data sets we analyzed are periodic. Apart from the annual cycle due to seasonal variations, periodicities shorter than the 11 year sunspot cycle, ~ 3, ~ 4, ~ 6 years, have been confirmed. Periodicities to which theses short periodicities (shorter than Hale period) may be corresponding are not yet known. Longer periodicities possibly related to Gleissberg cycles, ~ 55, ~ 120 years, can be also seen. However, periodicity comparable to the 11 year solar cycle seems absent in both EDI and the constructed data sets.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.39 no.1
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• pp.155-163
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• 2019

The knowledge about drought propagation is very important in accurate estimation of hydrological drought characteristics and efficient development of early warning system. This study investigated a probabilistic relationship of drought propagation based on Bayesian network model for historic period and for future projection under climate change scenario RCP 8.5 over the Han River basin. The results revealed that the propagation rate and lag time have increasing and decreasing trends from the historic period of 1967-2013 to the future periods of 2014-2053 and 2054-2100 under climate change, respectively. The probabilistic results of Bayesian model revealed that the probability of occurrence of lag time varied spatially and decreased when the intensity of meteorological drought changed from moderate to severe and extreme condition during 1967-2013. The values of probability increased in the first future period of 2014-2053 in several sub-basins and slight decreased in the second period of 2054-2100. The proposed probabilistic results will be useful for the decision makers to develop related policies with an appropriate insight toward the future drought status.

• Economic and Environmental Geology
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• v.54 no.6
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• pp.649-657
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• 2021

This paper aims to study the impact of natural disasters on per capita income in Vietnam both the short and long-term, specifically impact loss of income caused by the extreme drought 2013 for agriculture, forestry and fishery in Phu Yen Province, Central Vietnam. The study valued economic damage by applying the synthetic control method (SCM), which is a statistical method to evaluate the effect of an intervention (e.g. natural disasters) in different case studies. It estimates what would have happened to the treatment group if it had not received the treatment by constructing a weighted combination of control units (e.g. control provinces). The results showed that the 2013 drought caused a decrease in income per capita, mainly in the agriculture, forestry, and fishery sector in Phu Yen. The reduced income was estimated to be VND 160,000 (1 USD = 23,500 VND (2021)) for one person per month, accounting for 11% of total income per capita and continued to affect the income 6 years later. Therefore, authorities need to invest in preventive solutions such as early and accurate warnings to help people to be more proactive in disaster prevention.