Water resource is a vital factor in supporting the sustainable development of human society and the Earth system. However, the freshwater on the Earth is facing a severe crisis today due to population growth, increased demand for industrial and domestic water, and climate change (Famiglietti, 2014;Rodell et al., 2018;Vorosmarty et al., 2010). China's per capita water resources are only a quarter of the global average, and it is one of the 13 countries with the poorest water resources per capita in the world (L. Zhang et al., 2009). Moreover, the available water resources in China are unevenly distributed in space and time, with remarkable contradictions between water supply and demand. Limited freshwater resources are currently the main bottleneck of Chinese economic and social development (Xia et al., 2011). Therefore, monitoring the dynamic changes in freshwater on land and understanding the impact of different factors on water resources is of great significance for making water management policies and mitigating water resources crisis.