Efects Of Disaster Climatic Characteristics During Rice And Rape Key Growing Stage On Rice And Rape Production In The Lower Reaches Of Yangtze River Last 30 Years

The lower reaches of Yangtze River is not only China’s major rice-rapeseed production area,but also one of the areas which were largely affected by potential impact of climate change.For the regional adjustment of agricultural structure and the development of agricultural disaster prevention and mitigation measures,it is of great significance that assessing the impact of disaster climate during rice and rape key growing stage on rice and rape production.In this paper,climate dates and records of rice and rape yield over the period during 1980-2009 in the lower reaches of Yangtze River was collected.Mathematical statistics methods were conducted to reveal the temporal and spatial variation of disaster climate characteristics during rice and rape key growing stage.Correlation analysis and linear regression analysis were carried out to analyse the effect of disaster climate factors on crop yield,in order to provide a theoretical basis for developing appropriate measures to cope with disaster climate in the future.The main conclusions were as follows:1.An upward trend was found out in minimum temperature during rape wintering period in the lower reaches of Yangtze River(1989-2009).The number of days which minimum temperature is less than-5℃ during rape wintering period in Anhui and Jiangsu provinces significantly reduced,but the years which the number of days greater than three days is still exist.From analysis of the spatial characteristics,the number of days which minimum temperature is less than-5℃ in most areas of Anhui and Jiangsu provinces in 1980s was greater than three days,and nearly 10 years area of the region which the number of days greater than three days significantly reduced.2.In the lower reaches of Yangtze River,minimum temperature during rape squaring to flowering showed a significant upward trend by 0.09-0.13℃ per year since 1980s,.The number of days which minimum temperature is less than 0℃ during rape squaring to flowering stage showed a downward trend.From analysis of the spatial characteristics,minimum temperature during budding to flowering in the southern region was higher,while nearly 10 years the case of minimum temperature<0℃ was rarely.From 1980s to 2000s,the number of days which minimum temperature is less than 0℃ in most parts of northern partition(Anhui and Jiangsu Provinces)were significantly reduced during budding to flowering,but the number of days were still more than three days.Especially in the most northern region,the number of days which minimum temperature is less than 0℃ exceeded 5 days.3.Throughout 1980-2009 average values of precipitation during rape silique maturity stage(March to May)in the lower reaches of Yangtze river,except in Jiangsu province,the average annual rainfall of the other three provinces and city were higher than 250mm,especially in Zhejiang Province the average value was more than 400mm.Integrated spatial and temporal distribution of precipitation,we found a few more years which rainfall was more than 250mm in Shanghai.In Zhejiang Province,areas which precipitation was larger are mainly concentrated in the southwest.Anhui and Jiangsu provinces showed lack of precipitation in the north,and more precipitation in the south.Due to moderate precipitation in Jiangsu Province,the possibility of waterlogging occurred in Jiangsu province was small,4.In the lower reaches of Yangtze River,freezing injury during rape wintering period and squaring stage had declined since 1980s.Year of severe and moderate freezing injury significantly reduced,the number of year which present no and mild freezing injury increased significantly.From 1980s to 2000s,the severity of waterlogging during March to May was different in study region.In south division(Shanghai and Zhejiang),year of mild and moderate waterlogging was more,the number of year which no waterlogging and severe waterlogging existed was less.In northern district(Anhui and Jiangsu)did not occur waterlogging in most years and the year occurred waterlogging was only mild disaster year.5.The influence of disaster climatic factors during rape key growing stages on yield of rape was different in the lower reaches of Yangtze River(1980-2009).Large rainfall from March to May had a negative effect on rape yield in the lower reaches of Yangtze River,especially had a significant impact on rape yield in Anhui and Zhejiang provinces.Minimum temperature during squaring to flowering had positive effect on rape yield in most areas of the lower reaches of Yangtze River,rapeseed yield in Zhejiang,Jiangsu and Anhui provinces were highly significant positive correlation.The impact of minimum temperature during rape wintering period on rapeseed production in the lower reaches of Yangtze River was not very clear.Minimum temperature during wintering period had an increasing effect on rapeseed yield in Jiangsu and Zhejiang province,and there was a significant correlation of rapeseed yield in Zhejiang Province.6.In the lower reaches of Yangtze River,both minimum temperature and average temperature from heading to maturing on rice showed a significant upward trend since 1980s.The past 10 years rice yield in Zhejiang province and Shanghai had less affected by low-temperature damage.Nearly 30 years the number of days which average temperature is less than 20℃ between heading and maturity stage on rice in Anhui and Jiangsu provinces significantly reduced,but the year which the number of days was more than three days was still remain.Reviewing the spatial characteristics,in 1980s the number of days which average temperature is less than 20℃ in most areas of Anhui and Jiangsu Provinces was greater than five days,while nearly 10 years area of the region which the number of days more than 5 days was significantly reduced.Throughout 1980-2009,a significant downward trend was found out in chilling injury grading from heading to maturing on rice in the lower reaches of Yangtze River.The occurrence of severe chilling was less,moderate chilling injury year reduced significantly and the number of year which presented no and mild chilling injury increased significantly.The effect of minimum temperature and average temperature from heading stage to ripe period on rice yields in the lower reaches of the Yangtze River were positive.The impact of both minimum temperature and average temperature on rice yield in Zhejiang Province was maximum,which rice yield significantly increased;and the impact was smallest on rice yield in Anhui provinces.7.Booting and flowering are the most sensitive stages of rice to high temperature stress.Several heat stress indices were developed to quantify heat intensity,frequency,and duration between booting and flowering based on measured maximum temperature records of the last 30 years from 219 stations in the main rice-growing region of China.The heat stress(HSD,HSI,and HDD)between booting and flowering increased faster in EC subregion and SW subregion,indicating that heat stress between booting and flowering in CC was more severe than the cast and west subregion.The trend of heat stress between booting and flowering has increased in the last decades in most of the main rice production areas of China,but the rate was higher in Sichuan(SC)Province,Chongqing(CQ),south Jiangsu(JS)Province and southwest Yunnan(YN)Province.8.Heat degree-days(HDD)considering the duration and intensity of heat stress was required to describe the correlation of heat stress and yield variability.Significant negative impacts of the variability of heat stress on the observed grain yield were found in CC and SW,while no significant impacts was found in EC.Since heat stress is a major cause of yield loss and the number of heat events is projected to increase in the future,quantifying the future impact of heat stress on rice production and developing appropriate adaptation and mitigation strategies are critical for developing food security in Northern China.