A crop-specific dynamic irrigation scheme in a regional land surface-hydrologic modeling framework for improving human water-use estimation and irrigation impact assessment

Irrigation has a notable impact on the natural environment by changing the water and energy balance at the land surface and thereby altering atmospheric processes. Assessing these impacts and estimating irrigation water demand often involves using process-based models that incorporate the representation of irrigation practices. However, current irrigation schemes are primarily tailored to arid and semi-arid regions, and there is a research gap for humid multi-cropping rice regions. In response, this study introduces a Crop-specific Dynamic Irrigation (CDI) scheme, seamlessly integrated into the land surface-hydrologic model NOAH-HMS. This development enables the differentiation of irrigation practices for rice and non-rice crops, facilitating more accurate estimates of water demand for irrigation. The newly developed model is applied to an important cropping region in southern China, the Poyang Lake Basin (PLB), where the rice cultivation area accounts for over 60% of all crop cultivation. Compared to the widely used traditional Dynamic Irrigation (DI) scheme, integrating CDI into NOAH-HMS improves the model performance in simulating irrigation water amount over the PLB, with a mean relative error between 2007–2015 reduced by 39%, and a correlation coefficient increased by +0.26. The identified impacts on the surface water and energy balance are more pronounced at local scale, especially over the intensively irrigated areas. The performed interannual variability analysis demonstrates that our irrigation scheme CDI developed in this study allows to estimate irrigation water use under different drought conditions and has the applicability of mitigating risks of crop failures due to for example compound dry and hot. We conclude that our Crop-specific Dynamic Irrigation scheme is highly advantageous for multi-cropping rice regions and holds the potential for expansion into the fully coupled atmospheric-hydrologic systems with a more comprehensive representation of human activities.