Colonize the desert vs. retreat to the mountains: The evolution of city-water relationships in the Tarim river basin over the past 2000 years

Global climate change and anthropogenic disturbances have seriously affected sustainable development in drylands, where coordinated city-water relationships (CWRs) are foundational. The largest dryland in Northwest China, the Tarim River Basin (TRB) faces severe sustainability challenges; however, its long-term CWRs are poorly understood due to the scarcity of literature and records. This study utilized historical ruin sites to reconstruct city data and determine the evolution of the TRB city-water system over the past 2000 years. A driving mechanism framework for drylands was proposed to explain the CWR evolution mechanisms. The results revealed that 1) the cities exhibited an “outward-inward” movement trend in the “desert-plain-mountain” continuum; they first colonized near the central desert, subsequently retreated to the surrounding plains and then to the peripheral mountains, and finally returned to the plains. 2) The overall correlation coefficient between the number of cities and the length of rivers was 0.734 (p value < 0.001), which fluctuated over time. 3) Furthermore, climate change, water conservancy projects, population and arable land growth and wars exerted significant effects on the evolutionary process. The TRB's experiences and methods could help analyze city-water relationships in similar regions and promote sustainable development of drylands worldwide.