Abstract
ABSTRACT In recent decades, the rice cultivation regions in the Mekong Delta have continuously suffered from unprecedented weather events due to a decline in rainfall as part of climate variability. The aim of this study was to perform a comprehensive exploration of the rainfall characteristics across the area, applying the Rainfall Anomaly Index (RAI), Spearman Rho test and Sen slope estimator to help track the weather as well as provide warnings on the potential risks caused by alterations in rainfall amounts. For this goal, the rainfall data sequences at 14 national observation stations across the Mekong Delta were collected for the 1984 - 2019 period. Results indicated that the dry weather seasons occurred more frequently during the normally wet weather seasons. Four typical dry weather seasons were identified for the 1997 - 1998, 2002 - 2004, 2014 - 2016, and 2018 - 2019 periods. Among these, the 2014 - 2016 period was the driest, with 9 out of 12 stations in the area being extremely dry and RAI risk peaks as high as -4.86 at the Moc Hoa station in the province of Long An. A weather trend of decreasing rainfall was evident, mainly in the coastal sub-regions. The discovery of changing rainfall trends is valuable for predicting future climate variability.
Highlights
Drought is known as a natural disaster that often appears from a persistent deficiency of rainfall compared with the average value over a long time period (Mayowa et al, 2015; Becker et al, 2021), leading to a lack of freshwater for serving life, agricultural activities, and other sectors (CGIAR, 2015; Zarch et al, 2015)
The monthly rainfall sequences in the 1984 - 2019 period at 14 national normal observation stations across the area were converted to annual rainfall values to detect homogeneity with the Pettitt test, the Standard Normal Homogeneity Test (SNHT) and Buishand test
At a 95% confidence level, the critical values for 12 of the rainfall stations after applying the Pettitt test, the SNHT test and Buishand test were larger than the values of α while those for the Vi Thanh and Phu Quoc stations recorded values less than α (Table 3)
Summary
Drought is known as a natural disaster that often appears from a persistent deficiency of rainfall compared with the average value over a long time period (Mayowa et al, 2015; Becker et al, 2021), leading to a lack of freshwater for serving life, agricultural activities, and other sectors (CGIAR, 2015; Zarch et al, 2015). In Vietnam, drought represents the most extreme natural threat to the socio-economic sector, and especially to agricultural production (Dang, 2021). Vietnam recorded an extreme drought event in 2019 in 5 of 13 provinces in the Mekong Delta, and an emergency was declared. This devastating drought damaged up to 30% of 29,900 ha rice, 4,566 ha of shrimp, and approximately 43,583 ha of forest. Rainfall deficiency resulting in drought, leads to large global economic losses each year in the agricultural sector (UNVN, 2020; Junges et al, 2019). Studies on rainfall characteristics provide useful information that can help to better manage water resources for domestic use and especially plant crop irrigation (UNVN, 2020; Carvalho et al, 2020)
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