Exploring the Coupling and Decoupling Relationships between Urbanization Quality and Water Resources Constraint Intensity: Spatiotemporal Analysis for Northwest China

China is faced with great challenges for its low urbanization quality and high water stress. Moreover, the relationship between urbanization quality and water resources is still ambiguous. Therefore, we firstly constructed an urbanization quality index (UQI) and a water resources constraint intensity index (WRCI) by a fuzzy comprehensive evaluation method with multi-objectives and multi-hierarchies. Secondly, based on the concept and method of “coupling” and “decoupling”, we provided a method to explore the coordinated and uncoordinated relationships between UQI and WRCI from a spatiotemporal perspective. Finally, we used the statistical data of 51 prefecture level regions in Northwest China from the period 2000–2014 to analyze the spatiotemporal variation of the coupling and decoupling relationships between UQI and WRCI. Results show that, the UQI and WRCI in the whole Northwest China both belonged to low level, and that they had achieved strong decoupling during 2000–2014. However, the coupling and decoupling relationships between UQI and WRCI in Northwest China had great spatial disparity. From the HL-type regions (regions with high UQI & low WRCI) and strong decoupling type regions, we can find key development areas of Northwest China, where the relationships between UQI and WRCI were optimal and coordinated. From the LH-type regions (regions with low UQI & high WRCI) and strong negative decoupling type regions, we can find key problem areas, where the relationships between UQI and WRCI were the worst and uncoordinated. Our study developed an effective method for evaluating the sustainable development level of urbanization constrained by water resources in Northwest China and similar regions, which is significant for the New-Type Urbanization research in China.