Spatiotemporal dynamics of water supply–demand patterns under large-scale paddy expansion: Implications for regional sustainable water resource management

Climate change and large-scale paddy field expansion have altered the balance of water supply–demand in the Sanjiang Plain, a substantial commercial grain base in the high-latitude region of China. However, the matching pattern of water supply–demand throughout the growing period during the rapid expansion processes of paddy fields remains unknown. Hence, this study aimed to analyze the spatial–temporal variation characteristics of effective precipitation (Pem), crop water demand (ETc), supply–demand matching degree (MD), and irrigation water demand (IR) for different growing periods of paddy fields in the Sanjiang Plain using high-resolution meteorological and multi-period rice distribution data sets. The results showed that the area of paddy fields increased by 446% (20,064 km2) from 1990 to 2020 and almost completely covered the lowland of the Sanjiang Plain in 2020. ETc showed a slightly increasing trend initially and decreased afterward, while Pem and MD marginally increased at first and considerably increased subsequently during 1990–1995 and 2000–2020, respectively. MD has largely increased since 2000 in the Jiansanjiang area and the lower reaches of the Songhua River, where the largest paddy field expansion was experienced. However, the regional IR increased rapidly after 2000, which was associated with the expansion of paddy fields and further exceeded the carrying capacity of regional water resources. The efficiency of water resource utilization should be urgently improved, and integrated water resource planning and management should be implemented considering precipitation, surface water (regional water resources and transit water resources), and groundwater to promote the sustainable development of regional agriculture.