| Based on the daily temperature,precipitation and sunshine data and monthly temperature and precipitation data of 117 meteorological stations in the main early rice producing areas of China from 1960 to 2017 in the early rice growing season,Using standardized precipitation evapotranspiration index(SPEI),accumulated temperature,M-K mutation test,wavelet analysis,meteorological yield,gray correlation,etc.To study the temporal and spatial variation characteristics of agroclimatic resources and meteorological disasters in the early rice growing season of the early rice growing areas,and the effects on early rice,The aim is to provide a theoretical basis for China’s early rice to cope with future climate change and provide technical support for the potential of early rice yield increase.The results show that:(1)In the past 58 years,the average maximum and minimum temperature,average temperature,extreme minimum and maximum temperature,accumulated temperature(≥10℃)and frequency of high-temperature heat damage in the growing season of the study area showed an upward trend,while the frequency of cold in late spring and May showed a downward trend.In terms of time variation,the average temperature of early rice growing season in the study area showed a very significant upward trend in the past 58 years,with a tendency rate of 0.17℃/10a.After 1990s,the range of temperature rise increased;the average minimum and maximum temperatures,extreme minimum and maximum temperatures all showed a significant upward trend.The accumulated temperature(≥10℃)showed a very significant upward trend,with a tendency rate of 20.9 d/lOa and an obvious increase at the beginning of the 21st century.From the point of view of spatial change,the spatial distribution of the tendency rates of the highest and lowest temperatures and extreme lowest temperatures were the same,both of which were decreasing from north to south.The region with the fastest heating rate was Zhejiang,and the region with the slowest heating rate was Guangxi,Guangdong and Fujian.The accumulated temperature(≥10℃)is higher in the South and lower in the north.Except for Badong,the tendency rate of accumulated temperature(≥10℃)is negatively increasing,and the other areas showed an upward trend.The highest rate of increase is Cixi,Zhejiang(53.2℃/10a).On the whole,the accumulated temperature(≥10℃)shows a significant upward trend.In terms of time variation,the frequency and longest duration of late spring cold events in recent 58 years showed a significant decreasing trend,and the early rice in the 1960s-1980s study area was greatly affected by late spring cold,while the ratio of stations without late spring cold showed a significant upward trend,indicating that the area affected by late spring cold was narrowing.On the whole,the station-to-station ratio of late spring cold events at all levels showed a decreasing trend,with the lowest in 2000 s and the largest in 1960s and 1970s;the frequency of cold events in May showed a significant decreasing trend,with the average frequency of cold events in May being 0.56 times/a;the high-temperature heat damage showed a significant upward trend,and the frequency of high-temperature heat damage at all levels showed an upward trend;From the perspective of spatial change,the frequency of mild late spring cold decreases from north to south.The moderate and severe late spring cold have 68、98 sites occour a frequency of 0.Anhui and Zhejiang Province are the regions that are greatly affected by severe late spring cold.The average frequency of cold in May is higher in the north than in the South and higher in the elevation.The duration of cold in May is longer and the intensity of cold in May is higher in Zhejiang,Hunan,Anhui and Hubei.The highest frequency of high temperature hazards occurred in the Jiangxi of central part of the study area,and the lowest in the southern part of the study area is Guangdong and Guangxi and Fujian.16 years,24 years and 24 years are the first main periods of occurrence frequency of cold in late spring,cold in May and high temperature.(2)Rainfall days in the growing season of the study area showed a downward trend in recent 58 years.The maximum continuous 5-day precipitation,precipitation,precipitation intensity,rainstorm precipitation and rainstorm days in the critical period of early rice all showed an upward trend,and the study area tended to be wet in recent 33 years.In terms of time variation,the precipitation in early rice growing season showed an upward trend in recent 58 years,with the most precipitation in 1990s and the least in 1960s;the number of rainy days showed a fluctuating downward trend;the maximum continuous 5-day rainfall showed a significant upward trend,gradually rising after the mid-1990s;the precipitation intensity showed a very significant upward trend,and increased significantly after 1980s.From the point of view of spatial change,the annual average precipitation is generally high in the South and low in the north.About 74%of the stations show an upward trend.The fastest rate of decline is Wugang,Hunan(-17.45mm/10a),and the fastest rate of increase is Guangzhou(61.68mm/10a).The annual average and trend rate of rainfall days are high in the South and low in the north.93 stations show a downward trend.The fastest rate of decline is Dachen(-1.3d/10a),and the fastest rate of increase is Guangzhou(1.2d/10a).The distribution pattern of maximum 5-day continuous rainfall and precipitation intensity is consistent with that of rainfall,which indicates that precipitation intensity is closely related to rainfall.16 stations show a downward trend in precipitation intensity,while the others show an upward trend.24 years is the first main period of rainfall days.From the point of view of time variation,the larger the time scale of early rice growing season in the study area in recent 58 years,the smaller the fluctuation of SPEI value and the overall trend of drought,but the trend of wetting in recent 33 years.From the point of view of spatial change,the frequency of drought occurrence in April in the study area based on the monthly time scale showed a distribution pattern of high around and low in the middle.From April to July,the high value areas in the South and North tended to move towards the center.Based on the four-month time scale,the spatial distribution of drought occurrence frequencies of different grades is consistent.The high-value areas are the northern part of Hubei and Anhui,the southern part of Guangdong and Guangxi,the South of the Junction of Hunan and Jiangxi,and the eastern part of Fujian.The propensity rate of SPEI values based on the four-month scale is-0.16(10a)-1～0.16(10a)-1,and 64 sites show a downward trend.25 years is the first main period based on the SPEI values of four months time scale.From the point of view of time variation,the number of rainstorm days in the critical period of early rice in the study area showed a very significant upward trend in the past 58 years,declining before 90s and rising after 90s.From the point of view of spatial variation,the spatial distribution characteristics of rainstorm days and rainstorm precipitationt are consistent.The high value areas are in the south of the study area,and the junction of Hube、Anhui and Jiangxi.(3)In the past 58 years,the sunshine hours of early rice growing season and late growing season in the study area showed a very significant downward trend.The declining rates of sunshine hours in growing season and later growing season were-16.7h/10a and-12.2h/10a,respectively.From the point of view of spatial change,the average sunshine hours for many years decreases gradually from north to south,with 106 stations showing a downward trend;The distribution of sunshine hours in the late growing season was high in the north and south,low in the middle and high in the east and low in the west.In the late growing season,the sunshine hours at 110 stations showed a downward trend.The first main cycle is 22 years,which is consistent with the sunspot cycle.(4)Overall,agroclimatic resources have a significant impact on the meteorological yield of early rice in the study area.At present,water resources have the greatest impact on the yield of early rice in China,especially extreme precipitation has a very significant negative correlation with meteorological yield,followed by light resources and heat resources.The actual yield reduction of early rice in the study area is closely related to flooding.The fluctuation of meteorological yield in the study area and all provinces is large,and the negative value of meteorological yield coincides with the time of early rice yield reduction.Before 1990s,the fluctuation of meteorological yield of early rice was large,and after 1990s,the fluctuation was small;The correlation between heat resources and meteorological yield of early rice was strong,mean maximum temperature,mean temperature,extreme minimum temperature,late spring cold and high temperature heat hazards have strong correlation,meteorological yield in the study area is negatively correlated with frequency of late spring cold and high temperature heat hazards,and positively correlated with extreme minimum temperature.Water resources and meteorological yield show a significant negative correlation,especially the maximum continuous 5-day precipitation and precipitation intensity of extreme precipitation index show a very significant negative correlation.Therefore,the main early rice producing areas in China should actively prevent the adverse effects of extreme precipitation on early rice in order to improve the yield of early rice.The correlation degree and correlation of light resources are strong,mainly showing positive correlation,especially in Anhui,Guangxi,Hubei and Zhejiang. |
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