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Open AccessArticle

Trends and Extremes of Drought Episodes in Vietnam Sub-Regions during 1980–2017 at Different Timescales

1
Instituto Dom Luiz, Faculdade de Ciências da Universidade de Lisboa, 1749-016 Campo Grande, Portugal
2
Escola de Ciências e Tecnologia, Universidade de Trás-os-Montes e Alto Douro, 5001-801 Vila Real, Portugal
3
Environmental Physics Laboratory (EPhysLab), CIM-Uvigo, Universidade de Vigo, 32004 Ourense, Spain
4
Department of Meteorology and Climate Change, VNU University of Science, 334 Nguyen Trai, Thanh Xuan, Hanoi 100000, Vietnam
5
Department of Environmental Science, University of Sciences-Hue University, 77 Nguyen Hue Street, Hue 530000, Vietnam
*
Author to whom correspondence should be addressed.
Water 2020, 12(3), 813; https://doi.org/10.3390/w12030813
Received: 31 December 2019 / Revised: 7 March 2020 / Accepted: 10 March 2020 / Published: 14 March 2020
(This article belongs to the Special Issue Global Changes in Drought Frequency and Severity)
This study investigated the temporal occurrence of dry conditions in the seven climatic sub-regions of Vietnam during the 1980–2017 period. This assessment was performed using the Standardized Precipitation Evapotranspiration Index (SPEI) and the Standardized Precipitation Index (SPI) at 1 to 24 months timescales. Results show that the main periods of extreme drought occurred simultaneously throughout the country in 1992–1993 and 2003–2004, except for 2015–2016, when it was not identified in the southern region. In addition, a slight temporal lag was identified latitudinally (north–south) at the beginning of dry conditions, revealing the largest difference between the northern and southern regions. A positive trend in the time series of both indices (SPEI and SPI) prevailed in all sub-regions, with the SPEI minus SPI difference always being negative, suggesting the importance of temperature and evapotranspiration for this trend. Further detailed analyses were then performed using SPEI at 1-month and 12-months timescales for all climate sub-regions, as well as the main indicators to characterize duration and severity. Results show that the number of drought episodes did not vary much between regions, but they did vary in duration and severity at the annual scale. Moreover, changes in the soil root zone are largely associated with dry and wet conditions not only from season to season, but also in longer accumulation periods and more strongly in the northern regions of Vietnam. Indeed, a study of the most severe drought episodes also revealed the occurrence of negative anomalies of the root-soil moisture in the subsequent four or more months. Dynamic atmospheric conditions associated with the peak of most severe drought episodes show the crucial role of subsidence of dry air in the middle and high atmosphere, which prevents convection in the lower troposphere. Finally, the linkages between drought conditions in Vietnam and large-scale atmospheric and oceanic teleconnection patterns were revealed to be quite different among northern and southern sub-regions. During the positive phase of El Niño–Southern Oscillation (ENSO), drought episodes at different timescales were identified in the southern climate sub-regions, while the negative phase was associated with drought conditions in the northern regions. View Full-Text
Keywords: droughts; Vietnam; SPEI; soil moisture; teleconnection patterns droughts; Vietnam; SPEI; soil moisture; teleconnection patterns
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MDPI and ACS Style

Stojanovic, M.; Liberato, M.L.R.; Sorí, R.; Vázquez, M.; Phan-Van, T.; Duongvan, H.; Hoang Cong, T.; Nguyen, P.N.B.; Nieto, R.; Gimeno, L. Trends and Extremes of Drought Episodes in Vietnam Sub-Regions during 1980–2017 at Different Timescales. Water 2020, 12, 813. https://doi.org/10.3390/w12030813

AMA Style

Stojanovic M, Liberato MLR, Sorí R, Vázquez M, Phan-Van T, Duongvan H, Hoang Cong T, Nguyen PNB, Nieto R, Gimeno L. Trends and Extremes of Drought Episodes in Vietnam Sub-Regions during 1980–2017 at Different Timescales. Water. 2020; 12(3):813. https://doi.org/10.3390/w12030813

Chicago/Turabian Style

Stojanovic, Milica; Liberato, Margarida L.R.; Sorí, Rogert; Vázquez, Marta; Phan-Van, Tan; Duongvan, Hieu; Hoang Cong, Tin; Nguyen, Phuong N.B.; Nieto, Raquel; Gimeno, Luis. 2020. "Trends and Extremes of Drought Episodes in Vietnam Sub-Regions during 1980–2017 at Different Timescales" Water 12, no. 3: 813. https://doi.org/10.3390/w12030813

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