Comparison of spatial-temporal distribution characteristics of water temperatures between Lancang River and Mekong River

Water temperature(WT)is one of the important indicators of water body physical properties.Under- standing the characteristics of spatial-temporal variation on WT in the river continuum will help to de- velop the rational river-water-resource utilization plan,to avoid the possible ecology crisis,and to take full advantages of the natural resources in the involved region.As the biggest international river con- tinuum in Asia,the Lancang-Mekong river subregion(known as Greater Mekong Subregion,GMS)has become a famous economic,political,and ecological natural territory.This study examined the spa- tial-temporal distribution characteristics of the Lancang River water temperature,using the observa- tional data of WT values from 11 hydrological stations in 1960s.Furthermore,the WT differences be- tween Yunjinghong hydrological station(one representative station in China)and Chiang Saen hydro- logical station(one representative station in Thailand)were analyzed.Results indicated that:1)Water temperature was higher in the lower part of the river continuum than the upper part.Latitude variation is the main influencing factor.This effect is more obvious in dry season than in rainy season,more obvious in winter than in summer,and more obvious of the average minimum WT than the average maximum WT;2)WT difference between the upper and the lower parts of the river continuum was de- creasing due to little increase of WT in the upper part(Yunjinghong hydrological station)and obvious decrease of the WT in the lower part(Chiang Saen hydrological station)during the research period. Therefore,the parameters of WT are affected by the latitude,and the Lancang-Mekong river continuum lies in the north-south direction,so the tropical aquatic creatures,such as the tropical aquatic fishes, cannot survive in the upper part of this river continuum in winter season,while in summer season,the tropical aquatic creatures properly swim to the upper stream.The water temperature in the lower Me- kong River is mainly influenced by the regional water temperature and regional climate change.