Assessing cotton flooding disasters accompanied by high temperatures: A case study in the middle and lower reaches of the Yangtze River, China

Due to climate change, flooding disasters accompanied by high temperatures (FL-HT) are becoming increasingly common during cotton growing seasons, severely restricting cotton production. However, the characteristics and impacts of cotton FL-HT have rarely been investigated at the regional scale. In this work, based on existing field FL-HT research, we employed daily air temperatures and an agrometeorological indicator called the standardized antecedent precipitation evapotranspiration index to establish a novel approach to characterize FL-HT events during different cotton growth stages in the middle and lower reaches of the Yangtze River (MLRYR) during 1961–2020. Additionally, the influence of accompanying high temperatures (AHT) on the yield-reducing effect of cotton flooding was examined. The results demonstrated that more than half of the cotton FL-HT events were submonthly events, which were efficiently captured by our approach. Over the past six decades, the temporal trends of the cotton FL-HT frequency, the AHT intensity, and the conversion rate (from flooding to FL-HT) were upward at 83.0 % of the sites within the MLRYR, and up to 36 sites exhibited significant (p<0.05) increasing trends. In the most recent decade (the 2010s), the historic highs of the indicators were detected, as demonstrated by the most frequent FL-HT events (780 counts), the most intensive AHT, and the highest conversion rate (20.9 %). During the flowering and boll-filling stage, all the indicators were much greater than those during the other stages; the conversion rate reached 42.2 %, and the FL-HT frequency accounted for 63.0 % of the total FL-HT frequency over the whole growth period. Spatially, 43 % of cotton FL-HT events occurred in the southeastern MLRYR, which was identified as the region most affected by cotton FL-HT. The gravity centers of the cotton FL-HT indicators in different decades exhibited a northward-moving trend. Finally, according to the correlations between flooding intensity and cotton climatic yield, the yield-reducing effect of flooding was much stronger in the years with greater AHT (6 districts had significant correlations) than in the years with less AHT (only 2 districts had significant correlations), verifying the strengthening effect of AHT in cotton in response to flooding. In summary, this work provides new insights into monitoring cotton flooding-HT disasters and reducing flooding risk under climate change.