Evaluating Influences of the Manwan Dam and Climate Variability on the Hydrology of the Lancang-Mekong River, Yunnan Province, Southwest China

Abstract

Hydrologic alteration can be attributed to climate and human effects with some confidence. However, when quantifying the hydrologic alteration induced by dams using historical flow records, there is a lack of consideration concerning the impacts of climate variability on hydrologic alteration. Evaluating dam-induced and climate-influence-induced hydrologic alteration has emerged as a key problem, which is the process of quantifying the extent that they have altered the river’s hydrologic attributes. Central to this process is restoring the hydrologic attributes without dam influence. This study simulates hydrologic regimes without dam influence and evaluates the dam and climate influences on hydrologic processes in the Lancang-Mekong River. The results showed that the meteorological variables were closely related with runoff. Therefore, a stepwise-regression model was established and validated using meteorological variables with their time lags, and it showed good performance. The simulative evaluation revealed that runoff from the Lancang River was simultaneously and significantly affected by dam construction and climate variability, and the damming effects were mainly concentrated in the primary stage of reservoir operation. Meanwhile, the dam operation increased the minimum and maximum monthly runoff over a year. During the study period, the degree of hydrologic alteration (DHA) indicated that the Manwan Dam compensated for the impacts of climate variability on the Lancang River.