Assessment of paddy expansion impact on regional climate using WRF model: a case study in Sanjiang Plain, Northeast China

Paddy expansion changes land use types and increases irrigation, which results in altering surface-atmosphere energy flux exchange processes with an additional impact of increase in temperature. The paddy fields have expanded approximately 14 times in the Sanjiang Plain since the 1990s. The main conversion sources for this expansion are dryland, wetland, and woodland. This expansion in paddy area induced by different sources has an integrated effect on regional climate that may produce warming or cooling effect, with different intensities in different zones. In this study, two numerical experiments (case A and case B) were designed to simulate the impacts of paddy expansion on temperature and energy flux by using the Weather Research and Forecasting (WRF) model. Irrigation cannot be ignored that it is considered a unique agricultural management measure for paddy field compared to other land covers. And considered to depict paddy expansion process accurately, multiple remote sensing-based vegetation indexes, such as green vegetation fraction (GVF) and surface albedo (ALB) were incorporated to specify the vegetation properties induced by paddy expansion. Hegang concentrated expansion zones (HGCE), Fuyuan concentrated expansion zones (FYCE), Tongjiang concentrated expansion zones (TJCE), and Sanjiang Plain expansion zones (SJPE) were selected for this research. The results revealed that paddy expansion decreased the near-surface temperature. Cumulative temperature declined by 0.80 °C (HGCE), 0.61 °C (FYCE), 0.69 °C (TJCE), and 0.43 °C (SJPE) from June to September with more significant near-surface cooling in summer (July and August). In terms of energy balance, an increase in latent heat (LH) and ground heat flux (G) and a decrease in sensible heat (SH) were observed, but the impact of paddy expansion was more significant on LH, followed by SH and G, respectively. This study provides valuable information for future agricultural activities adjustment and mitigating climate change at the regional scale.