*3.2. The Land Conversion of Paddy Field, Dryland, and Other Land*

The spatial distribution of the land-use changes among paddy field, dryland, and other land from 1990 to 2020 is shown in Figure 5.

**Figure 5.** Land conversion between paddy field, dryland, and other land from 1990 to 2020.

In terms of the loss of paddy fields, the transition from paddy field to dryland was concentrated in Sichuan, Hebei, and Liaoning provinces. The seasonal water shortage and the decline in groundwater levels may be the major reasons for this change. On the North China Plain, long-term planting and industrial production induces sever groundwater shortages, which form a huge groundwater "funnel" in China. To reduce massive water usage, the government is actively encouraging farmers to change paddy field to dryland by providing subsidies [25]. In Sichuan, seasonal drought occurs frequently due to the spatial– temporal variability of rainfall. Eighty percent of the rainfall in Sichuan is concentrated

in May to September. In spring and canicular days, the possibility of droughts is higher than 60% [26]. The transition from paddy field to other land was mostly concentrated in areas with higher urbanization levels, such as the Yangtze River Delta, the Pearl River Delta, and Chengdu–Chongqing. Taking the Yangtze River Delta as an example, fertile land and a temperate climate are beneficial for agricultural production. As one of the richest regions, the Yangtze River Delta contributes more than 20% GDP yearly to the whole country. However, most construction land is transformed from paddy field in this area [27]. Thus, a spatial overlap can be seen between the high-quality paddy fields and economically developed areas [5,9]. As a result, massive losses of paddy fields with better hydrothermal conditions should be protected against with stronger practices, especially in rapidly urbanized areas.

In terms of newly added paddy fields, most of the new paddy fields in the north came from the old drylands, especially in central Henan Province, central Jiangsu Province, and eastern Heilongjiang Province (Table S5 in the Supplementary Materials). In Henan Province, as the hub of the ecological protection and high-quality development strategy of the Yellow River Basin and the Mid-Line of the South–North Water Diversion Project [28], the local paddy field had a good geographical advantage, which helped supply water resources and plain farming and provided the basis for the transition from dryland to paddy fields. In Jiangsu Province, local land consolidation planning policies encouraged the change from dryland plantations to a rice–wheat rotation to increase the economic value of arable land output. This kind of policy support provided a strong incentive for transitioning from local dryland to paddy field. In eastern Heilongjiang Province, the long-term conservation of massive amounts of fertile black soil on the plain area and the flood control projects for rice fields provided sufficient advantages for the transition from dryland to paddy field. Moreover, the consolidation projects of low-yield fields helped to improve the centralization of paddy field patches. In general, paddy field has higher economic benefits (for instance, rice has a higher price compared to wheat and corn), which stimulates farmers to change their dryland to paddy field to obtain a higher income. Because paddy field is a non-negligible source of carbon emissions [29], the transition from dryland to paddy field may lead to an increase in greenhouse gas emissions, which needs further monitoring in future research.

In terms of drylands loss, the transition from dryland to paddy field was concentrated in the central part of Henan Province, the central part of Jiangsu Province, and the eastern part of Heilongjiang Province. The transition from dryland to other land was mainly concentrated in the periphery of urban agglomerations such as the Beijing–Tianjin–Hebei Region. It can be seen that the larger-scale reduced dryland was concentrated in zones with a better natural resource endowment and a stronger economic location.

In terms of the newly added drylands, the transition from paddy field to dryland was concentrated in Sichuan, Hebei, and Liaoning, and a larger scale of converting other land to dryland was more concentrated in Xinjiang and Guangxi. Among them, converting other land to dryland in Guangxi was mainly concentrated in the west of Guangxi, and the primary source of new, local dryland was the reclamation of abandoned industrial and mining land. The new dryland came from areas with poor suitability for development and utilization.
