Temperature and Precipitation Variability and Its Effects on Streamflow in the Upstream Regions of the Lancang-Mekong and Nu-Salween Rivers

摘要

Hydrological regimes of alpine rivers are highly sensitive to climate variability/change. Temperature and precipitation variability and its effects on streamflow in the upstream regions of the Lancang-Mekong River (LMR) and Nu-Salween River (NSR) are examined in this study based on long-term observational data from 16 meteorological stations and 2 hydrological stations between the 1950s and 2010. This study employs the Mann-Kendall nonparametric test, together with the trend-free prewhitening (TFPW) approach to test trends and the Breaks For Additive Season and Trend (BFAST) method to detect abrupt changes in the hydrometeorological time series. The relations between air temperature, precipitation, and streamflow trends are assessed using random forest regression. The results show significant climate warming and related prevalent positive precipitation trends both at the annual and seasonal scale. A substantial precipitation increase paralleling climate warming, especially in spring, was also observed. However, no consistent abrupt change in meteorological time series was found. The increasing trends of streamflow with climate warming are seen both for the outlets of the LMR and NSR upstream regions, with the abrupt changes occurring in the mid-1960s and the late 1990s, respectively. The relation of streamflow to annual and wet season precipitation is pronounced, especially for the upstream region of the LMR with a percent variance explained of more than 65%. However, the relatively minor linkage of streamflow to air temperature and dry season precipitation may be confounded by the climate warming-driven changes in snowpack, permafrost, glacier, and evapotranspiration. These results could provide further a reference for the regional water resources management under climate change scenarios.