Acknowledgements
We would like to express our best gratitude for Prof Joseph Holden
(School of Geography, University of Leeds) for reviewing and providing
suggestions to improve the manuscript. This work is supported by the
National Natural Science Foundation of China (grant number NSFC
41850410497; NSFC 41807063), the Ningbo Municipal Bureau of Science and
Technology (Grant number 201401C5008005) and Grant of Shaanxi Provincial
Department of Education (19JK0522).