Figure. 3 Oasis area and proportion variations in Tuha Basin
from 1990 to 2020.
4.2 Oasis transition process
analysis
Oasis transition process was reflected in Figure 4 through nodes and
edges in the oasis transition network. The width of the edges in the
subgraphs referred to the converted areas from one node to another. The
complexity of the network was decided by the numbers of nodes and edges.
Generally, the interactions among all the land types became more
frequent from 1990 to 2020, with more edges connecting the nodes.
Grassland owned the most edges, proving the most active node in the
oasis transition network. The interaction between cropland and shrubland
was dramatic during the first three periods from 1990 to 2005, and kept
steady in the last three periods. There was no transfer-out of built-up
to other land types from 1990 to 2000, and the edge of the transfer-in
type was substantially wider than the transfer-out one throughout the
whole study period.
To reduce the redundancy of the network, principal component analysis
was conducted by calculating the main components nodes and edges that
had the edge weights with above-average values in the oasis transition
network (Figure 5). The primary conversions occurred among grassland,
cropland, shrubland, and Bare land. The interaction between grassland
and bare land dominated in the oasis transition network throughout the
whole study period; the transition between bare land and shrubland was
predominant after 1995. The weight of cropland gradually decreased until
it was below the average weight, at which point it was eliminated as a
primary component in the oasis transition network in the period of
2015-2020.