Figure.6 Transition of different oasis types in Tuha Basin during 1990 and 2020 (a), and area of oasis transition statistic (b)

4.3 Identification of key land type

Betweenness centrality was calculated for all nodes in the oasis transition network (Figure 7) to reveal the importance of nodes and identify the key land types in the oasis transition network. During the six sub-periods, grassland had the highest betweenness centrality with value 17.67, 11.33, 10.67, 12.17, 7.33, and 3.18, respectively, proving the most important type in the oasis transition process. Grassland was transferred in mostly from cropland and bare land, and transferred out to shrubland. However, the betweenness centrality showed descend tendency as the oasis expansion and more complicated topological relationship among the land types. The second highest betweenness centrality was cropland, with the values of 2.67, 3.83, 4.67, 3.33, 4.83 and 2.78, respectively during the six sub-periods. Betweenness centrality of cropland was close to grassland in 2015-2020, becoming the key land types in oasis transition network. Furthermore, the betweenness centrality of bare land was 5.50 in 2015-2020, revealing that it was also a key land type.