Effect of reservoir construction on vegetation drought and its driving mechanisms in Lancang-Mekong River Basin

Abstract

[Objective] Understanding the driving processes of meteorological-hydrological droughts on vegetation drought after reservoir construction helps enhance monitoring and early warning systems for vegetation drought in river basins. [Methods] Focusing on the Lancang-Mekong(LM) River Basin, the evolution characteristics of meteorological, hydrological, and vegetation droughts from 1982 to 2016 were analyzed based on three drought indices: Standardized Precipitation Index(SPI), Standardized Runoff Index(SRI), and Vegetation Condition Index(VCI). Pearson correlation analysis and lag analysis were used to explore the variations in relationships between different drought indices and the variations in drought response time(DRT) before and after reservoir construction. Finally, the effects of meteorological-hydrological droughts on vegetation drought and their driving mechanisms were investigated. [Results] The result showed that during the period from 1982 to 2016, meteorological-hydrological droughts in the basin exhibited similar trends, while vegetation drought showed significant seasonal variations and a gradual inter-annual increasing trend(0.02~0.37/a). After reservoir construction, the correlation between vegetation drought and meteorological drought decreased significantly in the downstream areas, while the correlation between vegetation drought and hydrological drought increased significantly in the upstream areas, showing a negative relationship. Additionally, significant changes were observed in the response time of vegetation drought to meteorological and hydrological droughts. During the dry season, the response time of vegetation drought to meteorological drought extended by an average of 1.6 months, while the response time to hydrological drought shortened by 0.2 months in the Vientiane-Pakse region, and extended by an average of 3.2 months in other regions. During the wet season, the response time of vegetation drought to hydrological drought extended by an average of 2.6 months. Furthermore, the response time of vegetation drought to meteorological drought varied across different regions: it decreased by 2.3 months on average in the China-Chiang Saen, Chiang Saen-Vientiane, and Pakse-Mouth regions, but increased by 3.8 months in the Vientiane-Pakse region. [Conclusion] The result indicate that reservoir construction in the basin alleviates vegetation drought in the Lancang-Mekong River Basin. The findings can enhance the ecological benefit evaluation of reservoir construction and improve the understanding of the response processes of meteorological, hydrological, and vegetation droughts.

Keywords

Langcang-Mekong River Basin / reservoir construction / meteorological-hydrological droughts / vegetation drought / response relationship / influencing factors