Analysis of irrigation demands of rice: Irrigation decision-making needs to consider future rainfall

Water-saving irrigation technologies (WSIs) for rice are widely used in China and are represented by alternate wetting and drying irrigation (AWD); however, there has been a lack of long-term series simulations to inves-tigate whether irrigation water inputs are saved using AWD all the time. To ascertain the performance of AWD in six rice areas across China and to improve performance, in this work, 13 typical stations, including AWD and flooded irrigation (FI), in six major rice regions of China were selected, and the rice irrigation demands of the typical stations from 2000 to 2020 were derived using the water balance model of paddy fields. The performance of AWD in different regions during different hydrological years were analyzed. The results indicated that the amount and frequency of irrigation were reduced using AWD in most cases, while some even increased (the ratio of increase accounted for 33% in late rice of Hengyang), which was especially obvious in dry years, followed by normal years and less so in wet years. The key reason for the above results was that future rainfall was not considered in the implementation of the WSIs, and "rainfall occurs after irrigation" gave rise to a regretful waste of both irrigation water and natural rainfall. Furthermore, in our cases, the use of AWD to save water contributed to an increase in the effective use of rainfall and a reduction in both irrigation and drainage. Hence, improving the effective use of rainfall is the key to water-saving irrigation of rice. Considering future rainfall can further enhance the water savings of AWD and effectively reduce needless irrigation.