Soil moisture in relation to lake fluctuations in a river-lake-basin system: A case study of the Poyang Lake region, China

•Study on correlation between soil moisture and lake fluctuation in a RLB system.•Annual storage decreases due to lake shrinkage in the Poyang Lake region, China.•Soil moisture helps to regulate the decreasing water storage of lake shrinkage.•Lake stores more water before July, land holds increasing water after that.•Soil moisture shows “funnel” pattern in summer and “island” in other seasons.