3.3.1. WEF changes
According to the results for the per capita WEF of the provinces (regions) in the YRB from 2003 to 2018, an analysis of the WEF temporal change in the basin was constructed, as shown in Fig. 5.
Figure 5 (a) shows the distribution of WEF of the provinces (regions) in the YRB. The spatial distribution of WEF varied significantly among the provinces (regions) in the basin. Compared to the upper and lower reaches of the YRB, the middle reaches had a higher WEF. Ningxia and Inner Mongolia had the highest annual WEF, which is similar to those obtained by Zuo et al. (2020), whereas Gansu and Shanxi had the lowest. Figure 5 (b) shows the temporal trend of per capita WEF in the basin from 2003 to 2018. As shown in the figure, the per capita WEF of the YRB generally showed a slow growth trend during the study period ,which was consistent with the trend of China (Sun & Zhang, 2017), indicating that, to maintain the rapid economic and social development of the YRB, water consumption also had to increase. From the perspective of the average annual growth rate, the average annual growth rate in the two stages before and after 2011 were 2.21% and 0.32%, respectively, and the growth rate decreased by 85.5%, indicating that the control of total water consumption in the YRB has achieved certain results, which is in line with the national strategic demand for high-quality development in the YRB.
From 2003 to 2018, the proportion of WEF in the provinces (regions) changed (Fig. 5 (c)), with Qinghai, Gansu, and Ningxia decreasing by 3.4%, 2.0%, and 3.5%, respectively, while Sichuan, Shaanxi, Shanxi, Henan, Inner Mongolia, and Shandong increasing by 4.9%, 1.6%, 0.58%, 1.9%, 0.24%, and 0.17%, respectively. Overall, although the water consumption in the middle and upper reaches of the YRB was relatively high, total regional water consumption control achieved good results. The total water consumption in the lower reaches of the basin continued to increase, which is not conducive to the sustainable use of water resources. Measures should be taken in the lower reaches to curb the excessive growth in water consumption and alleviate water consumption conflicts.
Figure 5 (d) shows the per capita WEF of each account in the YRB from 2003 to 2018, with significant differences in demands observed across the water-use sectors. As seen from the average contribution rate of WEF, the WEF of agriculture, industry, urban public, domestic, eco-environment, aquatic products, and water pollution accounted for 42.5%, 16.7%, 3.8%, 12.2%, 2.0%, 9.5%, and 13.3% of WEF, respectively, with the agricultural water footprint occupying a dominant position. Studies conducted on water ecological footprint of the lower Yellow River Basin (H. Li et al., 2020) and Henan Province (Jia et al., 2022) had also shown the same conclusion. As the largest agricultural production base in China, the YRB requires large quantities of water input for agricultural production. From the trends of WEF changes in various accounts, it can be concluded that the WEF of agriculture and industry showed decreasing trends, with average annual decline rates of 0.51% and 0.45%, respectively, whereas the remaining accounts maintained steady increasing trends, with average annual growth rates of 5.0%, 2.7%, 13.2%, 4.5%, and 3.0% for urban public, domestic, eco-environment, aquatic products, and water pollution WEF respectively. The eco-environment WEF accounted for the smallest proportion, but the average annual growth rate was the largest, indicating that, in the YRB, the ecological environment construction was of great importance, the concept of "green water and green mountain is the silver mountain of gold" was adhered to, and ecological protection and high-quality development of the YRB were promoted.
3.3.2. WEC changes
According to the results for the per capita WEC of the provinces (regions) in the YRB from 2003 to 2018, an analysis of the WEC temporal change in the basin was constructed, as shown in Fig. 6.
Figure 6 (a) shows the distribution map of WEC for the provinces (regions) in the basin. The WEC showed a decreasing trend from west to east. The WEC of Sichuan and Qinghai were the highest, and the same conclusion was obtained in the study of Y. Lu et al. (2021), because the source area of the Yellow River Basin is rich in precipitation (Zhang & Zhang, 2022) and has the largest total water resources. While that of Ningxia was the lowest and was 35 times lower than that of Sichuan. This is because Ningxia has the characteristics of aridity due to its geographical location (Wang et al., 2022). Due to geographical and climatic differences between the provinces(regions) in the basin, the spatial and temporal distributions of precipitation and total water resources were uneven, and the inter-annual changes in WEC in the different provinces (regions) varied. The per capita WEC in the YRB was maintained at 0.026–0.039 hm2/cap, with an annual average of 0.032 hm2/cap (Fig. 6 (b)).
3.3.3. WED and WES changes
Based on the per capita WEF and WEC of the provinces (regions) in the YRB from 2003–2018, the per capita WED and WES of each province (region) in the basin were calculated. The per capita WED and WES of the YRB from 2003–2018 were accounted for based on the per capita results for each province (region). The time changes in WED and WES conditions are plotted in Fig. 7.
The WEC in the YRB from 2003 to 2018 was much lower than the WEF, resulting in a water ecological deficit in water resource utilization in the YRB, with an average annual WED of 0.075 hm2/cap. The fluctuating changes in the WED with an increasing trend indicated that the contradiction between supply and demand of water in the YRB was prominent, and the water supply was far from meeting routine production and living requirements. Sustainable utilization of water resources faced a certain degree of threat. Similarly, the sustainable utilization of water resources in the Liaohe River Basin (Wang et al., 2013), central Wuhan (Wang et al., 2020b), Beijing and Tianjin (Y. Su et al., 2018) is not optimistic.
From 2003 to 2018, the WEC of Qinghai and Sichuan were much larger than the WEF, and these provinces had sufficient water ecological supply, indicating that the water resources of Qinghai and Sichuan were relatively abundant and that the supply of water resources could meet the local water demand. In addition to the above two provinces, the water resources of the remaining provinces (regions) showed different degrees of water ecological deficits, specifically Ningxia > Inner Mongolia > Henan > Shandong > Shaanxi > Shanxi > Gansu. These provinces (regions) have well-developed agricultural or energy industries that have a large demand for water resources, and the routine production and operation of life in these areas cannot be met by the supply of water resources in the basin alone.