As huge modifications are underway in the lower Mekong basin (LMB) in Southeast Asia by building dams and expanding irrigation areas, biodiversity, environment, and livelihoods are impacted. Climate change and variability is another driver that stresses this system. This has tremendously caused damages to agriculture, fisheries, and the livelihoods of people in the region. Also, since the flows are regulated through the dams, flows are altered, and their effect on environmental flows (EFs) are not fully known. For maintaining the species, functions, and resilience of freshwater ecosystems and livelihoods of human communities that depend on healthy ecosystems, it is critical that quality, quantity, and duration of water flows are monitored. Environmental flow requirement (EFR) is one such metric, and we investigate using flow duration curves for each dam site by explicitly considering the spatio-temporal variability and quantify the cascading impacts in the lower Mekong. This study will integrate flow data from several gauge stations in the basin and simulate flows using the macroscale hydrology model for the period between 1950 and 2018. For selected locations, EFRs for both wet and dry seasons will be presented. In summary, EFR for very low flow locations varies between 16.1% for Class A and 6% for cCass F, while the mainstem location needs 13.2% MAF for Class A and 9% for Class F during the wet season. However, dry season EFR for Class A was highest for very flow low locations (4.8%) but lowest for Class F (1.1%). The results of EFR in % and mean annual flows for multiple locations will also be discussed. The difference in the MAF between Class A and Class F was more for the wet season (7%) as compared to the dry season (2.8%), suggesting that careful water management plans would be required during the low precipitation period.
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