Changes in water supply and demand and their impacts on the yield for wheat-maize rotation in the Eastern Henan Plain of China

Assessing the alignment between crop water demand and effective precipitation facilitates the scientific optimization of irrigation systems and strengthens agricultural resilience. This study investigated a typical wheat-maize rotation system in eastern Henan Province of China. The crop water requirement (WRC), effective precipitation (Pe), and irrigation water requirement (IWR) for wheat and maize were calculated using daily meteorological data and grain yield statistics (1990–2022). Then the spatiotemporal patterns of water supply-demand matching under different precipitation year types were analyzed using climate trend analysis and spatial interpolation techniques. Furthermore, the water deficit index was employed to evaluate drought risk caused by water imbalances, while partial correlation analysis quantified the impact of water-related indices on wheat and maize yields. Key findings included: 1) The WRC and Pe of wheat exhibited "west-high-east-low" and "north-high-south-low" spatial gradients respectively. For maize, both parameters demonstrated "peripheral-high-center-low" patterns, with additional "northwest-high-southeast-low" differentiation. 2) In the past 33 years, The WRC and Pe of wheat and maize were shown an increasing and decreasing rend, respectively. However, the increase of WRC had been less than the increase in Pe during the growth period of wheat in most areas of eastern Henan, resulting in an increasing trend of wheat supply being less than the demand. The decrease of WRC was lower than the decrease of Pe during the growth period of maize, resulting in an increasing trend of maize supply exceeding the demand. 3) IWR of wheat escalated from 60 mm (wet years) to 176 mm (normal) and 263 mm (dry years). Historical analysis revealed predominant moderate (125 mm IWR) and mild (20 mm IWR) drought occurrences during middle-late growth stages of wheat. Strategic mid-season irrigation had effectively mitigated drought impacts, ensuring stable wheat yields. 4) In the dry year of maize growth period, water resources may also be less than demand, which would evolve into drought in some years. As the precipitation increased, the excess IWR of maize in normal and wet years could reach -120 and -300 mm respectively. From dry years to wet years, the frequency of extreme precipitation and continuous rainy during maize growth was not only higher, but also easy to compound. The excess of water resources supply over demand for maize had a negative impact on yield.