Vegetation responses to an ecological water conveyance project in the lower reaches of the Heihe River basin

Abstract

AbstractThe lower reaches of the Heihe River basin (HHLR), which is located in arid and semiarid areas of Northwest China, has experienced severe environmental deterioration in the past several decades. The ecological water conveyance project was initiated by the Chinese Government in 2000 to address this degraded ecosystem.In this paper, runoff, vegetation changes, and the relationship between runoff and vegetation in different regions were explored after the project, normalized difference vegetation index (NDVI), as a proxy of vegetation cover. For the entire lower reaches, NDVI and runoff exhibit an increasing trend after the project. In spatial, 44% of the vegetation‐covered area is significantly increased; whereas, 37% also exhibits an insignificant increasing trend. Moreover, 15% of the vegetation‐covered area shows an insignificant decreasing trend, and 5% exhibits a significant decrease. Overall, vegetation in HHLR improved after the ecological water conveyance project. The maximum time lag for NDVI along the east river and runoff from the east river, NDVI in the Ejina Oasis and runoff from the east river and the east canal, and NDVI along the west river and runoff from the west river was 4, 4, 3, and 6 years, respectively. However, runoff from last year had a significant influence on the current year's NDVI for the east river and the east canal. Meanwhile, autumn runoff shows a significant influence on the next year's NDVI, and spring runoff is important to the current year's NDVI. So we concluded that it is reasonable to convey more water into HHLR in autumn and spring.