4. Results

4.1 Oasis changes in areas

The area and proportion of oasis area in Tuha Basin for different oasis types were counted from LULC data during1990 and 2020 in Tuha Basin. As shown in Figure 3, the oasis in Tuha Basin expanded between 1990 and 2020, with the area increasing from 14346.43 km2 to 19977.09 km2. Natural oasis expanded the most, with the area increasing from 11219.26 km2 to 15922.68 km2, the proportion increasing from 78.21% to 79.71%. Shrubland contributed the most expansion in natural oasis, with the area and proportion increasing from 1121.93 km2 to 4756.68 km2 and from 2.01% to 23.81%, respectively. Grassland was the largest oasis type, and averagely accounting for 3.91% of Tuha Basin for seven periods.
Artificial oasis also had a slight rising trend, with the area increasing from 3127.17 km2 to 4054.41 km2, the proportion decreasing from 21.79% to 20.29% during 1990 and 2020. Explicitly, cropland accounted the greatest number of artificial oasis, the area changing from 2914.63 km2 to 3597.91 km2, and the proportion decreasing by 18.01% in 2020 than that in 1990 with 20.31%. Artificial oasis expansion was mainly attributed to the increment of built-up, with the area from 213.53 km2 increasing to 456.50 km2, the proportion increasing from 1.48% to 2.28%.