Assessment of changes in oasis scale and water management in the arid Manas River Basin, north western China.

Modern water-saving irrigation technology has expanded the scale of agricultural oases in arid and semi-arid regions of China. In this study, we used Landsat MSS and Landsat TM/ETM remote sensing data to assess changes in oasis scale and water availability with reference to differing water management practices in the Manas River Basin of north-western China from 1975 to 2015. We used the water-heat balance index H0 to determine oasis stability over time and constructed a suitable-scale calculation model for arid and semi-arid regions to assess the suitable development scale and cultivated land area in the study area. The implementation of water-saving technology in 2000 effectively improved the utilization efficiency of water resources and accelerated the formation of artificial oases; these expanded by 3873.3 km2 while natural oasis area was reduced by 3485.0 km2. The oasis stability index H0 was less than the critical stability index of 0.5 throughout the study period, implying that these areas were in a metastable state and unsuitable for further development. Therefore, in order to improve oasis stability, both scale and agricultural area should be further controlled. At present, actual oasis scale exceeds appropriate scale by 1.1 times and agricultural area exceeds suitable area by 2.5 times. To ensure the stability of the oasis, its area should be maintained at 3942.28-4481.06 km2 and the cultivated land should be maintained at 1576.91-1792.42 km2.