Construction Of Wheat Dry Hot Wind Disaster Grade Index

Based on historical disaster data,meteorological data,wheat growth period data and soil moisture data,this study taking the dry and hot wind disasters of wheat in Huanghuai area and Hexi Corridor in North China as the research object,using the current meteorological industry standard of “Wheat Dry Heat Disaster Level”(QX/ Based on T 82—2007)(hereinafter referred to as “the standard”)and methods of historical hazard inversion and independent T-test,determines the relative humidity threshold of each soil layer on dry hot wind disasters and calculates the threshold with random reserved samples.Based on the disaster descriptions and self-organizing feature mapping network(SOM)method,the sample level is divided.According to the confidence interval of each sample meteorological factor 90%-99%,the factor threshold is determined to be the best candidate index and the return rate is calculated.Comparing the difference between the optimal candidate index and the current target return rate,the new high-temperature and low-humidity dry hot wind disaster index of Huanghuai in North China based on the threshold of soil relative humidity and the dry and hot dry wind disaster index after the Huanghuai rain in North China and the high-temperature and low-humidity dry hot wind disaster level indicators in Hexi,Gansu were constructed.Based on the classified samples of high temperature and low humidity dry hot wind disasters in the Huanghuai area of North China,the distribution law of the extreme values of the factors on the dry hot wind disaster day was explored,and the difference between the meteorological factors and the comprehensive factors of the comparison index was selected.The main conclusions are as follows:(1)The relative humidity values of the whole layer and layered soil layers are in accordance with the normal distribution and the soil relative humidity of the A and B samples in each soil layer are independent of each other and passed the significance test.The relative humidity of the whole layer and layered soil layer affects the dry-hot wind disaster thresholds between 58%-65% and 56%-75% and the threshold increases with the depth of the soil layer.(2)The coincidence rate of the relative humidity threshold of the whole layer and layered soil layer is between 72.5% and 85% and the average value is about 80% which can reflect the influence of soil relative humidity on dry and hot wind disaster of wheat better.Considering the factors such as threshold conformity rate and business application convenience,the relative humidity of soil with 10-20 cm soil is selected as the critical threshold for the influence of soil relative humidity on high temperature and low humidity dry hot wind disaster in North China.(3)The newly constructed high-temperature and low-humidity dry-hot wind hazard grade index based on soil relative humidity and the high-temperature and low-humidity dry-hot wind hazard index of Hexi in Gansu Province have improved the ability to reflect the daily maximum temperature in the dry hot wind hazard factor.The best alternative indicators for the rate and the standardization have increased by 17%-37%.The threshold value of the meteorological factors of the dry and dry hot air indicators after the current standard is more than 72% which is better than the new generation of the optimal alternative index return rate and still has good applicability.(4)The three-factor(day maximum temperature,daily minimum relative humidity and daily maximum wind speed)of the high-temperature and low-humidity dry hot wind disaster day in North China are relatively consistent.The three-factor extreme value of the Class A sample mainly appears at 14 o'clock.The minimum daily relative humidity and daily maximum wind speed of the Class B sample mainly occurres at 15 o'clock and the daily maximum temperature mainly appeares at 16 o'clock.(5)About analysis results of the time difference of dry hot air index factors,the return rate of the highest daily temperature is higher than the return rate of the temperature at 14 o'clock.The return rate of the daily minimum relative humidity is not much different from the return rate of the 14 h relative humidity.The return rate of the maximum wind speed on the day is not much different from the return rate of the 14 o'clock wind speed.(6)The composite hot air index shows the comprehensive comparison results of the temperature,relative humidity and wind speed factors.The newly constructed level index selects the highest daily temperature,14 hours relative humidity and 14 hour wind speed whose mean value is above 60% which is much higher than the level return value of the 14-hour value and the daily extreme value.In summary,the rationality of the newly constructed dry hot wind hazard level index factor time selection day maximum temperature,14 o'clock relative humidity and 14 o'clock wind speed is verified.