Risk Analysis And Adaptation Measures Of Combined Heat And Cold Hazards For Double-season Rice Under The Changing Agro-climatic Resources

Under the background of global warming,different increments in temperature have been detected in regions,and a larger warming magnitude is recorded across the China's mainland.As an important rice cropping system in southern China,double-season rice is inevitable to be affected by climate change,especially threat from the changes of heat and cold hazards.It is necessary to take adaptation measures during double-season production in response to future continuous warming.Up to date,there is still lack of the research on thermal resource utilization under climate change,combined risk analysis of heat and cold hazards,as well as future adaptation in response to climate change for double-season rice.Based on the updated dataset of meteorology observation,phenology observation and climate projection,well-performed multi-models ensemble is obtained through downscaling methods and used to project future warming characteristics.Furthermore,the impact of climate change on thermal resource are assessed by the usage of thermal resource assessment index,and future thermal resource and risk dynamic of heat and cold hazards are projected based on well-performed multi-models ensemble across double-season rice planting area.For the purpose of minimizing disasters risk,the optimal adaptation is explored by adjusting sowing date,thermal accumulation and stress resistance.The main results are as follows:(1)There was an obvious bias between the outputs from 21 raw global climate models(GCMs)or regional climate model(here is Providing Regional Climates for Impacts Studies,PRECIS)and observation,which was much smaller after bias correction spatial disaggregation for GCMs(BCSD-GCMs)and bias correction for PRECIS(BC-PRECIS).The bias for mean temperature,maximum temperature,minimum temperature and diurnal temperature range between BCSD-GCMs/BC-PRECIS and observation was within±0.2 ^oC,which for frost days and heat days was within±2 d.The results projected from the ensemble of top five well-performed models individually for each climatic zones demonstrated that national warming would be characterized by increasing temperature with a rate of 0.64-0.67 ^oC·10a^-1,decreasing frost intensity with a rate of-4442 d·km²·10a^-1and increasing heat intensity with a rate of 3557 d·km²·10a^-1,during the period of 2006-2100 under RCP8.5.These rates could be nearly two times larger than that under RCP4.5.The warming increment would be higher in Xinjiang,Eastern part of Northwest China,Northeast China,North China,Inner Mongolia and Tibetan Plateau,while diurnal temperature range would be generally decreased.Besides,a significant downward trend in frost intensity would be expected in these zones,implying that the current colder areas would warm up much faster.A lower increment in temperatures and upward trend in diurnal temperature range would be projected in Huanghuai,Jianghuai,Jianghan,Jiangnan,South China and Southwestern China.A higher value and upward rate in heat intensity would be highlighted in Jianghuai,Jianghan,Jiangnan and South China,which were being prone to heat wave and would be more severe in the future.(2)Relative to 1986-2000,observed sowing date for double-season early rice during 2001-2015 was1-7 d earlier and to a small extent mature date for double-season late rice was postponed,while secure sowing date was 2-15 d earlier and secure mature date was 2-10 d delayed.The changes of sowing and mature date led to increase in useful accumulated temperature during actual and secure growing season,but the thermal resource utilization was generally worsen.In the future,secure sowing date for early rice would be in advance and mature date for late rice be postponed,which magnitudes under RCP8.5would be higher than RCP4.5.Moreover,the contribution of the prolongation in mature date to the longer secure growing season would be larger than that of the advancement in sowing date.Given longer secure growing season,accumulated temperature>=10 ^oC would increase in mid-to late-21th with larger increment under RCP8.5 than RCP4.5,which would be beneficial to utilizing more thermal resource and take adaptation.(3)There would be a decreasing trend in the risk probability of cold hazard for early and late rice but increasing trend in that of heat hazard for early rice under future scenarios.The risk probability of combined cold tress for early rice and cold hazard for late rice would tend to decrease,while that of other hazard combinations would decrease in 2021-2035 but increase after 2041.The risk assessment models of hazard shown that risk intensity of heat hazard would be larger than that of cold hazard,and risk intensity of heat hazard would tend to increase but that of cold hazard tend to decrease.Contrary to an obvious decreasing trend projected in the combined risk intensity of cold tress for early rice and cold hazard for late rice,the risk intensity of other combinations would be likely to increase,and higher risk would be highlighted in southern Jiangsu,northern Zhejiang,central Jiangxi and eastern Hunan.The characteristics of risk intensity for cold and heat hazard would be more obvious under RCP8.5compared to RCP4.5.(4)Under future change of thermal resource for double-season rice,yearly change of optimal adaptation in the future would elucidate a general advance in sowing date for early rice,a slight advance in mature date for early rice,a slight delay in sowing date for late rice,a general delay in mature date for late rice,a slight decrease in accumulated temperature during early rice growing season but a general increase in accumulated temperature during late rice growing season.At the spatial scale,the optimal sowing date for early rice would delay from south to north while that for late rice would delay from north to south.As time periods go on,there would be a general advance in optimal sowing date and mature date but a general decrease in accumulated temperature for early rice,and a general delay in sowing date and mature date but a general increase in accumulated temperature for late rice.Under the optimal adaptation of sowing date and accumulated temperature,accumulated stress temperature of cold hazard for early rice and late rice would be much smaller,but accumulated stress temperature of heat hazard for early rice would be larger and tend to increase in the future.In order to keep with the current accumulated stress temperature of heat hazard,much higher heat-resistance temperature threshold would be projected in the future and would be above 36.6 ^oC in 2081-2095 under RCP8.5.