Meteorological and Streamflow Droughts: Characteristics, Trends and Propagation in the Milwaukee River Basin

This study examined meteorological and streamflow droughts for the period 1951-2006 using the Milwaukee River basin in Wisconsin as the study area in an effort to improve the understanding of drought propagation. Specifically, this study aimed to answer the following research questions: (1) What are the temporal trends of meteorological and streamflow droughts identified by drought indicators? (2) How do the drought indicators manifest drought propagation? Meteorological droughts were identified using the Effective Drought Index (EDI), and streamflow droughts were identified using a threshold-level approach. The intensity and duration of both types of drought were found to have decreased over time most likely due to increasing precipitation. Therefore, 22 in the study area, and likely in the larger region, drought has become of less concern. The propagation of meteorological drought into streamflow drought was detected generally after moderate and severe sequences of negative EDI that eventually led to extreme meteorological drought events. The study finds that both EDI and the threshold-level approach are effective in diagnosing meteorological and streamflow drought events of all durations

Spatiotemporal Characteristics of Drought Occurrences over Japan

The drought climate of Japan from 1902 to 2009 was analyzed using an effective drought index (EDI). Drought regions were identified by hierarchical cluster analysis using drought characteristics (duration, severity, and onset and end dates) obtained from 50 observation stations. The results indicated that droughts could be divided into four groups (G1–G4) that reflected the local climate. The four groups were related to precipitation as follows. The summer rainy season affected groups G2–G4, in which droughts occurred mainly during spring and summer and were relieved before and after the rainy season. The G1 group was not affected by the summer rainy season and droughts were spread evenly throughout the year; it even had cases of droughts relieved by winter snow. All groups included dry conditions over the 108-yr period, and the driest conditions occurred in the late twentieth century. The statistical analysis of drought data showed that a total of 23 country-wide droughts occurred and that the most extreme droughts occurred in 1939–41 and 1984–85, with an EDI of −1.55. In addition, four dry seasons (1939–45, 1997–98, 1994–97, and 2005–09) were found using regime shift analysis. Regional droughts occurred 54, 54, 49, and 59 times in groups G1–G4, respectively. On average, short-term droughts with a duration shorter than 6 months occurred 3.5 times per decade, whereas long-term droughts extending over 1 yr occurred 0.3 times per decade. The drought duration and intensity were used to calculate the statistical return period of country-wide droughts. The 1939–41 drought had the longest return period, at 104.7 yr. The 1987–88 and 1995–97 droughts had return periods of 65.9 and 65.5 yr, respectively

Objective Quantification of Drought Severity and Duration

Common weaknesses of current drought indexes were analyzed. First, most of the current indexes are not precise enough in detecting the onset, end, and accumulated stress of drought. Second, they do not effectively take into account the aggravating effects of runoff and evapotranspiration, which build up with time. Third, they have a limited usefulness in monitoring ongoing drought because they are based on a monthly time step. Fourth, most of them fail to differentiate the effects of drought on surface and subsurface water supply. A new series of indexes are proposed to solve these weaknesses and to improve drought monitoring. In the new indexes, daily, rather than monthly, time steps are used. A new concept, effective precipitation (EP), the summed value of daily precipitation with a time-dependent reduction function, is proposed as a basic tool. Three additional indexes complement EP. The first index is each day’s mean of EP (MEP). This index shows climatological characteristics of precipitation as a water resource for a station or area. The second index is the deviation of EP (DEP) from the MEP. The third index is the standardized value of DEP (SEP). By using these three indexes, consecutive days of negative SEP, which can show the onset, the ending date, and the duration of a water deficit period is categorized. With the duration categorized, four additional indexes that can show drought severity are calculated: 1) accumulation of consecutive negative SEP, which shows the duration and severity of precipitation deficit together; 2) accumulated precipitation deficit, which shows precipitation departure from the normal during a defined period; 3) precipitation for the return to normal; and 4) effective drought index, a standardized index that can be used to assess drought severity worldwide. The merits and weaknesses of each index are compared. New quantified definitions on drought and its onset, end, and duration are proposed. These indexes were tested in the High Plains region of the United States from 1960 to 1996. The results were compared to historical reports of drought. From this analysis, it was concluded that the new indexes not only advanced objectivity, but also offered a number of advantages in practical use. These are 1) a more precise determination of drought duration, 2) the usefulness in monitoring an ongoing drought, and 3) the variety of ways a drought’s characteristics can be described

On The Mechanism Of The Naturally Formed Ice Spikes

The formations of the ice spike, which is the ice bar risen upward from the ice surface in bowl and has been known as a mystery of the Mt. Mai in Jinan, Jeonbuk Korea, are observed and analyzed through the observation records on more than 60,000 bowls of water for 8 years and 7 days and nights\u27 consecutive meteorological observations. Experiments making the ice bar in the refrigerator have also performed. As results, it is verified that the ice spike is not a mystery but a naturally grown ice bar caused by the volume expansion centralized to a certain point called breathing-hole when the status changes from water to ice. It is also verified that the ice spike grows by the synchronized cooling of the bowl not only on upper part but also on lower and side parts. In the breathing-hole that is the unfrozen part of the ice surface, it is caught with animated photographs that not the ice but the water rises upward like a farsighted eye glasses. At the edge of the rising water, the ice wall is formed by the evaporation cooling and the conduction from the cold air. Also, the peculiar meteorological conditions related to the formation of ice spike at the valley of the Mt. Mai is found. The 1st is that the the huge tafoni rocks of the Mt. Mai may make frequently the favorable temperature condition for ice spike, which is near zero degree Celsius, through the continuous evaporation and sublimation and raditive cooling. The 2nd is that lower topography of the area that permits only the slow intrusion of cooled air in the valley. The 3rd is the water in the valley that contains much air parcels obtained during the flow down through the cold tafoni rock

Quantitative definition and spatiotemporal distribution of little water season (LIWAS) in Korea

Like other continental climatic regions Korea has a period around the spring when agricultural activities are interrupted frequently by a shortage of available water resources during the season. This season, which is termed the Little Water Season (LIWAS) in this study, has important implications for many socio-economic activities but the scientific definition of this season remains vague. In this study, the onset and termination dates, as well as the characteristics of the LIWAS have been defined based on the Available Water Resources Index (AWRI). Based on the proposed definition of LIWAS, the implications on hydrological conditions over a range of geographic scales and their inter-annual variations on the water resource environments in Korea have been assessed. To develop an appropriate index for LIWAS based on AWRI, the criterion value (CV) for LIWAS was set as the lowest 25th percentile of the AWRI values averaged for 30 years (1981-2010). Therefore, the Little Water Season for Korea (LIWAS_K) was considered as the period when the daily averaged AWRIs were successively lower than the CV (143.7 mm). Based on this, the mean onset and end date of LIWAS_K, was 9 February and 11 May which also reflected the period in the spring season when the available water resources are expected to the lowest. Moreover, a number of seasonal characteristics of the water availability during the LIWAS, such as the Little Water Intensity (LWI), Water Deficit Amount (WDA) and Water Deficit Intensity (WDI) have been defined for the particular study region. Based on our results, we aver that the proposed season classification of the LIWAS can be better analyzed using the concept of usable water resources as a classification of dry period instead of using temperature and raw rainfall datasets

A Self-Calibrating Effective Drought Index (scEDI): Evaluation against Social Drought Impact Records over the Korean Peninsula (1777-2020)

The Effective Drought Index (EDI) is designed to monitor and characterize the drought condition at a daily scale, using the last 30 years of daily precipitation records as a climatic yardstick. A critique of the EDI is that the behavior of the index depends on the reference period, making comparisons of EDI values difficult over a long record period. Here, a self-calibrating EDI (scEDI) is calculated using the 244-year daily precipitation records (1777–2020) in Seoul, the Republic of Korea. The scEDI is evaluated by comparing with drought damage reports from the Annals of the Joseon Dynasty (1807–1907) and relevant online search activity volumes from Google Trends and NAVER DataLab data (2013–20). The scEDI automatically calibrates the behavior of the index over time by calculating the normal condition of antecedent precipitation based on a rolling 30-year period. As a result, the scEDI is more temporally comparable than the EDI, that is, droughts with the same intensity have the same frequency throughout the entire record period, regardless of wet and dry decades. Results show that a majority of drought damage records and spikes of public interest in droughts are found when droughts are moderate (-1.4 of scEDI) and severe (-2.0), respectively, implying that social drought impacts/response might occur during different intensities of an emerging drought. This study highlights the importance of temporally self-calibration when it comes to detecting and characterizing “social droughts” with social impact/response data over multi-centuries.11Nsciescopu

Drought prediction till 2100 under RCP 8.5 climate change scenarios for Korea

An important step in mitigating the negative impacts of drought requires effective methodologies for predicting the future events. This study utilizes the daily Effective Drought Index (EDI) to precisely and quantitatively predict future drought occurrences in Korea over the period 2014–2100. The EDI is computed from precipitation data generated by the regional climate model (HadGEM3-RA) under the Representative Concentration Pathway (RCP 8.5) scenario. Using this data for 678 grid points (12.5 km interval) groups of cluster regions with similar climates, the G1 (Northwest), G2 (Middle), G3 (Northeast) and G4 (Southern) regions, are constructed. Drought forecasting period is categorised into the early phase (EP, 2014-2040), middle phase (MP, 2041-2070) and latter phase (LP, 2071-2100). Future drought events are quantified and ranked according to the duration and intensity. Moreover, the occurrences of drought (when, where, how severe) within the clustered regions are represented as a spatial map over Korea. Based on the grid-point averages, the most severe future drought throughout the 87-year period are expected to occur in Namwon around 2039-2041 with peak intensity (minimum EDI) –3.54 and projected duration of 580 days. The most severe drought by cluster analysis is expected to occur in the G3 region with a mean intensity of –2.85 in 2027. Within the spatial area of investigation, 6 years of drought periodicity and a slight decrease in the peak intensity is noted. Finally a spatial-temporal drought map is constructed for all clusters and time-periods under consideration