Determining the contributions of soil moisture, climate and human activities to crop growth variations in the Eastern Henan Plain based on time-series SAR imagery

Quantifying the multiple influences on crop growth variation is essential for food security and the promotion of sustainable agricultural development. However, at the current stage, most studies focus on qualitative analysis of vegetation information using optical data. When exploring the driving forces of crop growth based on SAR imagery, there is an issue with the unclear quantification of contributions from multiple factors. Therefore, this paper proposes a new methodology based on time-series SAR imagery to determine the influence of relative surface soil moisture (RSSM), climate and human-dominated factors on crop growth changes. Firstly, a novel dual-polarized SAR vegetation index (DRVIs) has been introduced for long-time-series crop growth monitoring. Subsequently, the DRVIs are combined with the water cloud model to isolate vegetation's contribution further and achieve high-precision, wide-area retrieval of RSSM. Finally, the response mechanisms between crop growth, RSSM, and climate changes (temperature and precipitation) are explored through wavelet analysis and partial derivative methods, quantifying the contribution of each factor affecting crop growth and identifying the primary drivers. This study selected the Eastern Henan Plain as the study area and conducted the research based on 89 Sentinel-1 images from 2020 to 2022. Experimental results show that the contribution of ecoclimatic factors (including temperature, precipitation, and RSSM) to DRVIs variation is mainly distributed between -0.349 and 0.504, while human-dominated contributions to DRVIs variation mainly ranges from -0.502 to 0.347. Over the three years, DRVIs have declined due to the dominance of ecoclimatic factors and human-dominated contributions. Through comprehensive analysis of meteorological data, RSSM, and crop planting and yield, it can be observed that the declining trend of DRVIs is influenced by ecological and meteorological changes (such as flooding events) as well as a reduction in the planting area. This research could deepen the understanding of the relationship between crop growth variability and climatic, ecological, and land surface characteristics.