Evaluating agricultural drought and flood abrupt alternation: A case study of cotton in the middle-and-lower Yangtze River, China

Drought and flood abrupt alternations (DFAA) are new challenges under climate change with particular emphasis on its affects related to agriculture. However, current regional DFAA analysis research rarely investigates agri-cultural DFAA with special regards to agricultural elements. In this work, a method based on a daily scale index named the standardized antecedent precipitation evapotranspiration index (SAPEI) and crop characteristics was established to investigate the characteristics of agricultural DFAA during cotton growth stages in the middle-and -lower Yangtze River (MLRYR) during 1961-2020. Additionally, the influence of DFAA on cotton climatic yield in response to flooding and drought was examined by multiple regression. The results demonstrate that the SAPEI efficiently described the relations between cotton climatic yield and the intensities of cotton drought and flood and well characterized cotton DFAA events, especially for short-term events. The most recent decade over the past six decades has seen the most frequent cotton DFAA events, and the only significant trend (p < 0.05) of cotton DFAA frequency was an upward trend in Jiangsu Province. In addition, the middle growth stage of cotton was the most DFAA-affected period within a year. Cotton drought-flood alternations (DF) were more common than flood-drought alternations (FD). The most DF-prone and FD-prone regions differed greatly, but the north-eastern MLRYR was the most DFAA-prone region. In all provinces, the cotton DFAA frequency was significantly and positively related to the cotton drought frequency. Finally, the relations between cotton climatic yield and the intensities of drought and flood were much less significant in the years with more DFAA events than in other years, indicating an obvious negative interaction between drought and flood in cotton DFAA events. This finding, at the regional scale, confirmed previous field-scale conclusions on cotton responses to DFAA stress. In summary, this work provides references for agricultural water management in adapting to climate change.