Can Effective Drought Index (EDI) successfully characterise meteorological drought and seasonal agricultural losses?

<p>The nature and characteristics of drought are not like a flood, cyclone or storm surge since droughts cannot easily be tracked and are difficult to quantify as a distinct event. In this study, we examined the characteristics of meteorological drought occurrence and severity using the Effective Drought Index (EDI), including the drought events, drought chronology, onset and ending of drought, consecutive drought spells, drought frequency, intensity and severity, using North-Bengal of Bangladesh as a case study. The rainfall and temperature dataset of Bangladesh Meteorological Department (BMD) for the study region throughout 1979-2018 is utilised. The trends of drought are detected by using the Mann-Kendall test and Sen Slope estimation. We evaluated the performance of EDI using the Standardized Precipitation Index (SPI), historical drought records and rice production. The study finds that seasonal and annual droughts have become more frequent in all seasons except pre-monsoon. In addition, the largest decrease in seasonal EDI is found in the monsoon in both Teesta floodplain and Barind tract. In decades prior to the late 2000s, a drought spell typically started between March to May (± 15 days) and ended with the monsoonal rainfall in June/July. In the years since the last 2000s, monsoon and post-monsoon droughts spells have significantly increased. Overall, the peak intensities of droughts are higher in the Barind tract than in the Teesta floodplain, and the frequency and severity of moderate to severe drought are increasing significantly in the Barind tract. Though EDI is strongly correlated with the SPI index, EDI and rice production have a non-linear relationship and are not significantly correlated. Hence, this research suggests that there are other significant influences on yield rather than just climatological drought (e.g. irrigation, lack of technology and management etc.).</p>

Predicting the probability of transforming different classes of monthly droughts in Iran

The main objective of this study was to predict the transition probability of different drought classes by applying Homogenous and non- Homogenous Markov chain models. The daily precipitation data of 40 synoptic stations in Iran, for a period of 35 years (1983–2018), was used to access the study objectives. The Effective Drought Index (EDI) was applied to categorize Iran’s droughts. With the implementation of cluster analysis on the daily values of effective drought index (EDI), it was observed that Iran can be divided into five separate regions based on the behavior of the time series of the studied stations. The spatial mean of the effective drought index (EDI) of each region was also calculated. After forming the transition frequency matrix, the dependent and correlated test of data was conducted via chi-square test. The results of this test confirmed the assumption that the various drought classes are correlated in five studied regions. Eventually, after adjusting the transition probability matrix for the studied regions, the homogenous and non-homogenous Markov chains were modeled and Markov characteristics of droughts were extracted including various class probabilities of drought severity, the average expected residence time in each drought class, the expected first passage time from various classes of droughts to the wet classes, and the short-term prediction of various drought classes. Regarding these climate areas, the results showed that the probability of each category is reduced as the severity of drought increases from poor drought category to severe and very severe drought. In the non-homogeneous Markov chain, the probability of each category of drought for winter, spring, and fall indicated that the probability of weak drought category is more than other categories. Since the obtained anticipating results are dependent on the early months, they were more accurate than those of the homogeneous Markov chain. In general, both Markov chains showed favorable results that can be very useful for water resource planners.

Spatio-Temporal Assessment of Drought using Effective Drought Index (EDI) and Standardized Precipitation Index (SPI) During Monsoon Months in Cuttack District, Odisha, India

Various parts of the World is experiencing frequent droughts due to climatic uncertainties. Drought is the most difficult and least understood natural hazard which can occur virtually in all types of climatic regions. Therefore, improved scientific analysis for forecasting, monitoring and management of drought is required. Effective drought index (EDI) and Standardized Precipitation Index (SPI) is used for drought analysis in this study, as both indices gained popularity as important drought indicators in recent years across space and time. Therefore, EDI 3 Aug (June, July and August), SPI 3 Aug, EDI 3 Sep (July, August and September) and SPI 3 Sep are estimated by utilizing the monthly rainfall data for 30 (1988-2017) years in thirteen blocks of Cuttack District, Odisha, India for characterising drought during monsoon months. The analysis inferred that, highest number of total drought (moderate+severe+extreme) events occurred in Narasighpur block based on EDI 3 Aug and Tangi-Choudwar and Tigiria blocks based on both SPI 3 Aug. Similarly, maximum number of total droughts experienced by Salepur block based on EDI 3 Sep and Cuttack Sadar, Nischintakoili and Tangi-Choudwar blocks as per SPI 3 Sep. Drought maps prepared for the years in decades (1995, 2005 and 2015) to study the variation of drought spatially as well as temporally during monsoon months based on the computed value of drought using EDI and SPI. In the year 1995, no drought events are observed from the drought map based on the drought value of EDI and SPI. Two rainfall threshold values were also estimated for agricultural drought during monsoon months in this study. The threshold limit for agricultural drought varied from 553.9 to 706.3, 516.2 to 722.8, 614.1 to 687.4 and 586.0 to 702.0 mm based on EDI 3 Aug, SPI 3 Aug, EDI 3 Sep and SPI 3 Sep value respectively. This drought analysis will be helpful for implementing various strategies of water management and crop planning for different blocks of Cutttack District.

Evaluating the Spatiotemporal Characteristics of Agricultural Drought in Bangladesh Using Effective Drought Index

This study aims to assess the spatiotemporal characteristics of agricultural droughts in Bangladesh during 1981–2015 using the Effective Drought Index (EDI). Monthly precipitation data for 36 years (1980–2015) obtained from 27 metrological stations, were used in this study. The EDI performance was evaluated for four sub-regions over the country through comparisons with historical drought records identified by regional analysis. Analysis at a regional level showed that EDI could reasonably detect the drought years/events during the study period. The study also presented that the overall drought severity had increased during the past 35 years. The characteristics (severity and duration) of drought were also analyzed in terms of the spatiotemporal evolution of the frequency of drought events. It was found that the western and central regions of the country are comparatively more vulnerable to drought. Moreover, the southwestern region is more prone to extreme drought, whereas the central region is more prone to severe droughts. Besides, the central region was more prone to extra-long-term droughts, while the coastal areas in the southwestern as well as in the central and north-western regions were more prone to long-term droughts. The frequency of droughts in all categories significantly increased during the last quinquennial period (2011 to 2015). The seasonal analysis showed that the north-western areas were prone to extreme droughts during the Kharif (wet) and Rabi (dry) seasons. The central and northern regions were affected by recurring severe droughts in all cropping seasons. Further, the most significant increasing trend of the drought-affected area was observed within the central region, especially during the pre-monsoon (March–May) season. The results of this study can aid policymakers in the development of drought mitigation strategies in the future.

Evaluating the Spatiotemporal Characteristics of Meteorological Drought in Bangladesh Using Effective Drought Index

This study aims to assess the spatiotemporal characteristics of meteorological droughts in Bangladesh during 1981–2015 using the Effective Drought Index (EDI). Monthly precipitation data for 36 years (1980-2015) obtained from 27 metrological stations, were used in this study. The EDI performance was evaluated for four sub-regions over the country through comparisons with historical drought records identified at the regional scale. Analysis at a regional level showed that EDI could reasonably detect the drought years/events during the study period. The study also revealed that the overall drought severity had increased during the past 35 y; the most significant increasing trend was observed in the central region. The characteristics (severity and duration) of drought were also analysed in terms of spatiotemporal evolution of the frequency of drought events. It was found that the western and central regions of the country are comparatively more vulnerable to drought. Moreover, the southwestern region is more prone to extreme drought, whereas the central region is more prone to severe droughts. In addition, the central region was more prone to extra-long-term droughts, while the coastal areas in the southwestern as well as in the central and north-western region were more prone to long-term droughts. The frequency of droughts in all categories significantly increased during the last quinquennial period (2011 to 2015). The seasonal analysis showed that the north-western areas were prone to extreme droughts during the Kharif (wet) and Rabi (dry) seasons. The central and northern regions were affected by recurring severe droughts in all cropping seasons. Further, the most significant increasing trend of the drought-affected area was observed within the central region, especially during the pre-monsoon (March-May) season. The results of this study can aid policymakers in the development of drought mitigation strategies in the future.