Drought and Management Approach for Sustainability of Tropical Reservoir Ecosystem: A Case Study of Ubolratana Reservoir, the Most Productive Reservoir in the Northeast Thailand

Occurrences of drought disasters in tropical reservoir ecosystem are commonly due to limitations of water inflow that are related to impacts from climate changes. Research on integration of fifty-five years of information on the Ubolratana reservoir, the most productive reservoir in the northeast Thailand, indicated high fluctuated levels of inflows and storage volumes. In particular, the storage volumes during 2019-2020 were lower than the "Minimum Storage Level" determined for reservoir's sustainability. Such phenomenon reflects severe drought crisis in the reservoir area. Results implied that changes in the inflow had remarkable effect on economically important fishery resources. Results of the drought periods also indicated that quantities of organic suspended solids of reservoir water had decreased and may consequently influence biological production potentials of the reservoir ecosystem. In addition, decreased inflow and water storage contributed to the increased water retention time and, accordingly, enhanced frequent increases of potentially toxic blue green algae, in particular in the lacustrine zones. Overall, the research implied that drought disaster can deteriorate the quality of foods and habitats for aquatic living and, thus, decrease stability of ecosystem production. In management coping with such conditions, it is necessary to accelerate upstream rehabilitation in order to promote sufficient water volume. The inflow should be enhanced appropriately, while the outflow should be carefully managed, for conservative management of the reservoir resources. Proactive measures for habitat and water quality remediation should be developed and evaluated further.