| dc.description.abstract | Mekong River Basin (MRB) is one of the largest and most significant transboundary river basins in southeast Asia. In recent years, natural hazards compounded manmade vulnerability have affected to local people, resulting in further impacts on fisheries, agricultural productions, and river ecosystems in this region. This thesis presents characteristics of droughts, streamflow, and sediment loads in the MRB using three main methods, including historical data analysis, hydrological model, and machine learning techniques. In terms of El Niño Southern Oscillation (ENSO)-droughts connection, the correlation analysis between ENSO index and precipitation suggested that the strongest ENSO events in Dec-Jan-Feb may result in developments of meteorological drought in Mar-Apr-May, and further led to hydrological and agricultural drought in Apr-May-Jun. Such ENSO effects had significant influences on drought variabilities in southern MRB and were insignificant in the north. Results from changes in flow and sediment show that the river flow at Chiang Saen, which is the closest station to the Lancang cascade dams, has risen by 73.65\% in the dry season during 2012-2019 in comparison with the period 1970-1991 while that has reduced by 29.46\% in the wet season. Besides, the sediment loads have reduced by 69.15\% and 68.45\% at Chiang Saen and Kratie, respectively in the high-dam period (2012-2019), indicating a drastic reduction of sediment owing to the sediment trapping by Chinese dams in the upper MRB and local dams. For streamflow prediction, the proposed deep learning models were able to capture the fluctuation of river flow in the MRB during the period of high-dam development (2010-2019), with the Nash-Sutcliffe (NSE) values ranged from 0.79 to 0.88, and the Long short-term Memory (LSTM) still outperformed other models for streamflow prediction in an era of mega dams (NSE $geq$ 0.8). The results can be applied to the development of drought monitoring methods, water management, and supporting for development planning and strategic decision making, especially in the context of rapid development in the Mekong river basin. | en_US |