| With global warming,extreme rainfall events have increased,rainfall distribution has become more uneven,and floods have occurred frequently.Rainfall is also one of the important meteorological factors affecting the main growth stages of early rice.The frequency of occurrence of different grades of rainfall in the flood season before the study can predict the future trend of rainfall,and provide reasonable suggestions for the improvement of crop varieties such as early rice and planting planning.Based on the daily rainfall data of 90 surface meteorological stations in the first flood season from 1961 to 2016,this study divides the rainfall intensity into Light rain,Moderate rain,Heavy rain,Rainstorm,Downpour,Extraordinary rainstorm,and analyzes the trend change of rainfall frequency in different grades in the first flood season of guangxi.According to RMM(real-time Multivariate MJO)index,the activity period of atmospheric low-frequency oscillation was divided into 8 phases,and the activity intensity and propagation characteristics of atmospheric low-frequency oscillation of different phases and their influence on rainfall intensity in guangxi in the first flood season were analyzed by means of synthetic analysis.At the same time,the correlation coefficient method was used to determine the relationship between high intensity rainfall and early rice yield in the first flood season,and the following conclusions were drawn:(1)In the past 56 years,light rain in guangxi has a downward trend,with a trend rate of-1.312 days/year;Moderate rain shows a slight increase with a trend rate of 0.837 days/year;The trend rate of heavy rain,Rainstorm,Downpour,Extraordinary rainstorm was 0.983,0.589 and 0.266 days/year,respectively,showing a significant growth trend.(2)Through the analysis of 925 hpa water vapor flux divergence anomaly field,500 hpa height anomaly field and 200 hpa divergence anomaly field,the influence process and approach of atmospheric low-frequency oscillation on rainfall in guangxi in the first flood season are revealed.When the low-frequency oscillation of the atmosphere reaches to the second and fourth phases in the east,divergence occurs at 200 hpa in the upper air,near-surface airflow increases,and at 500 hpa,the southerly airflow on the east side of the anticyclone influences the southwest airflow from the bay of Bengal in guangxi.With 925 hpa water vapor transport strengthened,local water vapor convergence;The coordination of high and low air circulation is beneficial to the increase of local rainfall in guangxi.The fifth to seventh phases are the opposite,less affected by humid air flow and less rainfall.(3)At the same time,through the analysis,it is found that there is a significant negative correlation between high intensity rainfall and early rice yield in the first flood season,indicating that high intensity rainfall frequency will lead to early rice yield reduction in the same period.When the early rice was in the stage of tillering,flowering,jointing,booting and milk-ripening,which was sensitive to water requirement,the field waterlogging brought by high intensity rainfall would cause great harm to the early rice.The occurrence frequency of high-intensity rainfall in the first flood season of guangxi shows an increasing trend,which is closely related to the activity of MJO.The MJO increases the rainfall in guangxi through its influence on the circulation of low,medium and high altitude.The frequent occurrence of high intensity rainfall in the first flood season,coupled with strong convective rainfall,easily leads to flood disaster.High intensity rainfall in the first flood season is negatively correlated with the yield of early rice,that is,the increase of high intensity rainfall causes the yield reduction of early rice in the same period.Therefore,according to the change rules of high-intensity rainfall,early rice planting time should be arranged in a scientific and reasonable way,and protective measures should be taken to reduce the occurrence of early rice disaster. |
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