Impacts of large-scale climatic circulation on floods through precipitation and temperature in the Lancang-Mekong River Basin

The importance of large-scale climatic circulation impacts on precipitation and floods in the Lancang-Mekong River Basin (LMRB) has been widely acknowledged. However, the mechanisms related to the impacts of circulation on floods are not yet fully understood. To address this issue, circulations were characterized by using the climate indices, and floods were represented by the flood volume and simulated using an improved hydrologicalhydrodynamic model. The linear regression model was used to assess the impacts of circulation on precipitation and temperature, and also to quantify the impacts of precipitation, temperature, and circulation on floods. The results show that circulation affects precipitation with large spatial variability, while affects temperature with small spatial variability. On average, a unit change in different climate indices can cause a 2.5 %-6.1 % change in precipitation and a 0.3 %-1.2 % (0.09 degrees C-0.16 degrees C) change in temperature. Further, precipitation has a positive impact on floods, while temperature mainly has a negative impact. On average, a unit increase in precipitation , temperature can cause a 22.6 % increase and a 9.3 % decrease in floods, respectively. Consequently, cir-culation affects floods mainly through its impact on precipitation, while its impact on temperature also plays an important role. On average, a unit change in different climate indices can cause a 3.1 %-8.7 % change in floods. In addition, a multi-linear regression model was used to discuss the explained variance and relative contribution of climate. The results show that circulation can explain 12 %-23 % of the precipitation, temperature , flood variances, while temperature and precipitation can explain 69 % of the flood variance. Among all circulations, the monsoon systems, North Atlantic Oscillation, and El Nin similar to o-Southern Oscillation dominate precipitation, temperature, and floods in the LMRB with the largest contributions and the most affected regions.