Mitigating the impact of increased drought-flood abrupt alternation events under climate change: the role of reservoirs in the Lancang-Mekong River Basin

Abstract. The Lancang-Mekong River (LMR) Basin is highly vulnerable to extreme hydrological events, including Drought-Flood Abrupt Alternation (DFAA). The efficacy of potential mitigation measures, such as reservoir operations, on DFAA under climate change remains poorly understood. This study investigates these dynamics using five Global Climate Models (GCMs) from the Coupled Model Intercomparison Project Phase 6 (CMIP6). It employs the Revised Short-cycle Drought-Flood Abrupt Alteration Index (R-SDFAI), along with the Tsinghua Representative Elementary Watershed (THREW) model integrated with the developed reservoir module. The findings reveal that DFAA in the LMR Basin is primarily dominated by DTF (drought to flood), with probabilities of DTF exceeding those of FTD (flood to drought) at mild, moderate, and severe intensity levels. The increase in DTF probability for future periods is also significantly higher than that of FTD. Mild DTF and mild FTD account for 58 % to 90 % and 75 % to 100 % of their total probability in the future, making the mild-intensity events the most frequent DFAA. Reservoirs play a significant role in reducing DTF risks during both dry and wet seasons, though their effectiveness in controlling FTD risks, particularly during the dry season, is relatively weaker. Furthermore, there is a positive correlation between the reservoir's capacity to mitigate total DFAA risk and its total storage. Reservoirs display a stronger ability to regulate high-intensity FTD and high-frequency DTF events, and significantly reduce the monthly duration of DFAA. These insights provide valuable guidance for the effective management of water resources cooperatives across the LMR Basin.