Human-Induced Hydrological Droughts in Central Vietnam: A Study for River-Segment Analysis

The number of drought studies is increasing due to rising concerns about risk-informed agriculture and water resource management. However, while most of this information is derived from meteorological variables, the literature on human-induced drought for river segments is limited, especially in the tropical monsoon region. In this study, we quantify human-caused hydrological droughts in segments of the Vu Gia Thu Bon (VGTB) River basin in Central Vietnam. Our objective is to gain a deeper understanding of how human activities have altered the frequency, severity and duration of hydrological droughts between 1980 and 2020 and their impacts on freshwater supply and ecosystem sustainability. Specifically, we use the Soil and Water Assessment Tool (SWAT) to obtain hydrological outputs, along with the Standardised Runoff Index (SRI), Probability Density Function (PDF) and Cumulative Distribution Function (CDF) for dry conditions analysis. Based on the examination of drought patterns over the Vu Gia and Thu Bon rivers using the proposed river-segment analysis and reconstructed streamflow, we found a contrast in drought conditions between the Vu Gia (+28.9%) and Thu Bon (−26.4%) rivers. The Vu Gia River experienced more dry conditions and drought events from 2011 to 2020 compared to the Thu Bon River. In contrast, the Thu Bon River experienced more moderate to extremely wet conditions during the same period. In addition, drought has caused saltwater intrusion to increase in intensity and duration, resulting in an 11.8% reduction in rice paddies' area from 2010 to 2020. This study highlights our approach to measuring temporal and spatial changes over river segments, providing deeper insights into water transfers and their changes across river tributaries, linking with saltwater intrusion and land use and land cover (LULC) changes.