water Article Extreme Droughts Change in the Mekong River Basin: A Multidisciplinary Analysis Based on Satellite Data Vo Tuong 1 , Thanh-Van Hoang 2, * , Tien-Yin Chou 2 , Yao-Min Fang 2 , Chun-Tse Wang 2 , Thanh-Danh Tran 1 and Dung Duc Tran 3   Citation: Tuong, V.; Hoang, T.-V.; Chou, T.-Y.; Fang, Y.-M.; Wang, C.-T.; Tran, T.-D.; Tran, D.D. Extreme Droughts Change in the Mekong River Basin: A Multidisciplinary Analysis Based on Satellite Data. Water 2021, 13, 2682. https:// doi.org/10.3390/w13192682 Academic Editor: Su-Chin Chen Received: 3 September 2021 Accepted: 24 September 2021 Published: 28 September 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Faculty of Civil Engineering, Ho Chi Minh City Open University, Ho Chi Minh City 700000, Vietnam; voquangtuong@gmail.com (V.T.); danh.tt@ou.edu.vn (T.-D.T.) 2 Geographic Information System Research Center, Feng Chia University, 100 Wenhwa Rd., Situn, Taichung 40724, Taiwan; jimmy@gis.tw (T.-Y.C.); frankfang@gis.tw (Y.-M.F.); james@gis.tw (C.-T.W.) 3 Center of Water Management and Climate Change, Institute for Environment and Resources, Vietnam National University—Ho Chi Minh City (VNU-HCM), Ho Chi Minh City 700000, Vietnam; dungtranducvn@yahoo.com * Correspondence: van@gis.tw Abstract: This study evaluates droughts in the Mekong River Basin (MKB) based on a multidisci- plinary method, mainly using the Standardized Precipitation Index (SPI) and Mann–Kendall (MK) test. Precipitation data corresponding to the seasonality of the regional climate were retrieved from Integrated Multi-satellitE Retrievals for Global Precipitation Measurement from 2001 to 2020, at a monthly temporal scale and 0.1 degree spatial resolution. Drought events and their average interval, duration, and severity were determined based on Run theory. Our results revealed the most extreme drought period was in January 2014, at the time the lowest precipitation occurred. Spatial extreme drought results indicated that Zone 2 in the upstream MKB has the highest frequency of drought, with 44 events observed during 19 years, and experiences the most severe droughts, whereas Zone 24 in the downstream MKB has the most prolonged drought duration of seven months. The periods and locations of extreme drought were identified using the SPI, corresponding to historic droughts of the MKB. Furthermore, the MK test shows an increasing trend of droughts in the lower MKB and the cluster analysis identified six clusters of times series. Overall, our study provides essential findings for international and national water resource stakeholders in identifying trends of extreme drought in the MKB. Keywords: extreme drought; Mekong; SPI; Mann–Kendall; time series clustering; integrated multi- satellite retrievals (IMERG) 1. Introduction Drought is among those natural disasters that have caused severe damage to hu- manity, society, economy, and environment [1–6]. In the three recent decades, droughts have occurred in many countries across the world, such as the United States [7], Brazil [8], China [9], and Vietnam [10]. Drought has affected the socio-economy by reducing crop productivity, cultivated area, and crop yield. As a result, drought has increased agricul- tural production costs and decreased the income of agricultural labor. Furthermore, the prices of food could be highly influenced by droughts. Severe drought can have complex effects, ranging beyond the direct impacts on crops and livestock to an array of indirect impacts associated with sanitation, nutrition, loss of livelihood, displaced populations, and international disputes [5]. The Mekong River flows through China, Myanmar, Thailand, Laos, Cambodia, and Vietnam and its catchment basin covers an area of 797,000 km 2 with more than 60 million people. The river begins in the Lasagongma Spring in the plateaus of Tibet and flows about 4350 km southeast to the East Sea of Vietnam. The Mekong River basin is divided Water 2021, 13, 2682. https://doi.org/10.3390/w13192682 https://www.mdpi.com/journal/water