Heat Injury Risk Assessment for Single-Cropping Rice in the Middle and Lower Reaches of the Yangtze River under Climate Change

Under global warming,the risk of heat injury for crops increases,which leads to increasing instability in agricultural production.In this study,based on phenological observation data and yield data during 1981-2011 and daily meteorological data during 1961-2011 in the middle and lower reaches of the Yangtze River（MLRYR）,the risk of heat injury for single-cropping rice in this area and its response to climate change were assessed and analyzed.The risk was decomposed into such elements as hazard,exposure,vulnerability,and disaster prevention/mitigation capacity,in accordance with natural disaster risk assessment theory and the formation mechanisms of agrometeorological disasters.First,a hazard assessment model was established to identify spatiotemporal variations of the heat injury in the MLRYR during 1961-2011,and the relationship between heat injury hazard and air temperature was analyzed to identify the response of hazard to climate change.It was found that the heat injury hazard of single-cropping rice was positively correlated with the mean and maximum temperatures during the rice heading period of 20 days,with the hazard increasing sharply when the mean temperature exceeded26.5℃ and the maximum temperature exceeded 31℃.Then,exposure,vulnerability,and disaster prevention/mitigation capacity were also quantitatively examined.The results show that vulnerability and hazard were the two most important factors in the heat injury risk assessment for single-cropping rice at most stations in the MLRYR.The risk assessment considering only the first three natural elements produced high-risk values（〉 0.46）mainly in the northeast of the study area.By adding the regional capability in disaster prevention/mitigation into account,the risk assessment produced high-risk values in a much smaller area in the northeast but somewhat larger areas in the southwest of the study domain.In general,the risk of heat injury differed greatly within the MLRYR.Particular rice varieties should be adopted for specific regions,according to the local risk features quantified by this study.Under the warming climate,the risk of heat injury for single-cropping rice is likely to continue to increase.

Projection of Heat Injury to Single-Cropping Rice in the Middle and Lower Reaches of the Yangtze River, China under Future Global Warming Scenarios

Based on simulation results from the 16 CMIP5 model runs under three Representative Concentration Pathways(RCP2.6, RCP4.5, and RCP8.5) in combination with the recent five years of growth-stage data from agrometeorological observation stations in the middle and lower reaches of the Yangtze River, changes in heat injury and spatial distribution patterns of single-cropping rice in China during the early(2016–35), middle(2046–65), and late(2080–99) 21 st century were projected by using quantitative estimations. Relative to the reference period(1986–2005), the occurrence probabilities of heat injury to single-cropping rice under different RCP scenarios increased significantly, showing a trend of mild > moderate > severe. The occurrence probabilities increased with time and predicted emissions, especially the average and maximum occurrence probabilities, which were ～48% and ～80%,respectively, in the late 21 st century under the RCP8.5 scenario. The spatial patterns of the occurrence probabilities at each level of heat injury to single-cropping rice did not change, remaining high in the middle planting region and low in the east. The high-value areas were mainly in central Anhui and southeastern Hubei provinces, and the areas extended to the northwest and northeast of the cultivation area over time. Under the RCP2.6, RCP4.5, and RCP8.5 scenarios, the total area of heat injury to single-cropping rice showed a significant linear increasing trend of 7.4 × 10~3, 19.9× 10~3, and 35.3 × 10~3 ha yr^(–1), respectively, from 2016 to 2099, and the areas of heat injury were greatest in the late21 st century, accounting for ～25%, ～40%, and ～59% of the cultivation area.

南方水稻复种指数变化对国家粮食产能的影响及其政策启示（英文）

Changes in rice production in Southern China are crucial to national food security.This study employed Landsat images to map the distributions of paddy rice-cropping systems in Southern China in 1990 and 2015.The impact of rice multiple cropping index changes on grain production capacity was then evaluated.Three important results were obtained for the 1990 to 2015 study period.First,the multiple cropping index for rice decreased from 148.3% to 129.3%,and 253.16×10^4 ha of land area was converted from double-cropping to single- cropping rice,termed “double to single”.The area with the most dramatic changes is in the Middle-Lower Yangtze Plain.The rice-cropping system distribution in Southern China showed a change from north to south with double-cropping rice shrinking and single-cropping rice expanding.Second,the “double to single” conversion led to a reduction of 6.1% and 2.6% in rice and grain production,respectively.Hunan and Jiangxi Provinces,located in the main rice producing areas,and Zhejiang,which has shown better economic development,exhibited large reductions in rice production due to the “double to single” conversion,all exceeding 13%.Third,the grain production capacity of converted “double to single” paddy fields is equivalent to that of 223.3 × 10^4 ha of newly reclaimed cultivated land,which is 54% of the total newly cultivated land reclaimed through the 2001–2015 land consolidation project.It is also 1.7 times the target goal for newly cultivated land in the national land consolidation plan for 2016–2020.Making full use of the converted “double to single” paddy fields can save 167.44 billion yuan in newly reclaimed cultivated land costs.Therefore,instead of pursuing low-quality new arable land,it is better to make full use of the existing high-quality arable land.Based on these results,the government should change the assessment method for cultivated land balance,and incorporate the sown area increased by improving the multiple cropping index into the cultivated land compensation indicator.