Study On Dynamic Assessment And Zoning Of Comprehensive Risk Of Compound Drought And Heat Stress For Soybean In Northeast China

In the context of global warming,extreme heat has become more frequent,persistent,and intense,while drought conditions are expected to worsen,posing a serious threat to agricultural production.The "synergistic effect" of droughts and high temperatures has already led to reduced agricultural production in many areas.The Northeast China(NEC),which is the most important soybean-producing region in China,is experiencing more rapid warming than the national and global averages.Currently,there are concerns about declining soybean production capacity and acreage,as well as outstanding contradictions in planting structure.Therefore,the urgent task at present is to improve soybean production capacity,expand soybean cultivation,optimize the layout of soybean production,and mitigate the impact of meteorological disasters and resultant losses.Since the 21 st century,academic research on natural disaster risk assessment has evolved from a focus on single hazards to multi-hazards,from site-based to grid-based assessments,and from static to dynamic approaches.Research on the risks associated with compound drought and heat stress(i.e.,drought,high temperature,and high temperature drought)has become a research hotspot in the academic field as well as a practical issue that requires urgent attention from government and agriculture-related departments.Therefore,it is crucial to conduct dynamic assessments and zoning research on the comprehensive risk assessment of compound drought and heat stress in the NEC soybeanproducing region for national agricultural restructuring,ensuring food security,and formulating disaster prevention and mitigation measures.In this study,we applied the "four-factor" disaster risk formation theory to investigate the risk formation and climate change context of compound drought and heat stress in NEC soybean at different developmental stages.We utilized multi-source data fusion,controlled experiments,crop model scenario simulation,multi-model coupling,trend analysis,and correlation analysis to analyze meteorological,remote sensing,soil,crop,disaster,and socio-economic data.Then,meteorological(drought,high temperature,and compound drought and heat)indices,climate suitability indices,and comprehensive drought and heat indices were constructed to investigate the risk formation and climate change context of compound drought and heat stress of soybean in NEC.We also explored the distribution pattern of disasters and key factors affecting soybean yield,and established a comprehensive risk assessment framework that integrates probability distribution hazard assessment,crop model scenario vulnerability assessment,and comprehensive index system.Furthermore,we proposed a comprehensive risk assessment and zoning technology system for composite hazards and corresponding comprehensive risk management and adaptation strategies to avoid disaster.The main conclusions of this study are as follows.(1)Temporal and spatial distribution patterns of compound drought and heat in NEC and their effects on soybean yieldsThe growing season of soybean in NEC showed a trend of warm-dry during 1961-2020.Heilongjiang Province showed a trend of wetter in the early stage of the growing season The accuracy of disaster event identification was improved by using daily scale drought,high temperature,and compound drought and heat indices.The years 1982,2000,and 2007 were identified as typical drought,high temperature,and compound drought and heat years in NEC,respectively.The study also revealed cyclicity of changes in compound drought and heat intensity of approximately 19,42,and 30 years.Based on the Hurst index,it was predicted that the intensity of the compound drought and heat would continue to increase in the short term.The occurrence of disasters during the second developmental stage(flowering and podding)of soybean had the greatest impact on meteorological yield,with the degree of impact being compound drought and heat > drought > high temperature.(2)Dynamic assessment and zoning of the climatic suitability of soybean in NECThe farming region in NEC has experienced an increase in heat resources and a decrease in moisture and sunlight resources during 1961-2020.Using two methods,namely crop response function and zonal index affiliation function,the study investigated the climatic suitability of optimal soybean varieties in NEC by combining the climatic suitability of early,medium,and late maturing varieties.The results showed a decreasing trend in climatic suitability.The second method was found to be superior in expressing soybean yield distribution and yield stability,and the spatial distribution of suitability was close to the actual soybean planting distribution extracted from remote sensing.Based on the yield reduction rate,the climate suitability classes were classified as unsuitable,subsuitable,suitable,and most suitable.The refined climate zone of soybean climate suitability,which covered 1 km × 1 km farmland,had the largest area in the suitable class,and the most suitable area for soybean cultivation was decreasing as climate warming expanded to higher latitudes and altitudes.The climate suitability results can be used as a potential exposure to participate for comprehensive risk assessment.(3)Dynamic hazard assessment and zoning of the of compound drought and heat stress for soybean in NECThe study found that the Standardized Multiple Source Data Comprehensive Drought and Heat Index(SMCDHI)was superior to a single indicator in indicating drought impacts in NEC.It was found that 2001-2010 was the most severely affected by compound drought and heat stress in NEC.The daily hazard of compound drought and heat stress for soybean in NEC was highest in the early growing season,decreased rapidly in the middle of the season,and tended to increase in the late growing season.The overall spatial pattern of hazard was highest in the western part of the study area,followed by the eastern part and lowest in the central part.The hazard was divided into low,medium,high,and extremely high based on the levels of compound drought and heat stress,and the static zoning results for the three developmental stages of soybean had the highest coverage of high hazard(40.8%,36.4%,and 35.7%).The dynamic zoning results had the largest coverage of low hazard,with multi-year averages above72.5% for all developmental stages.However,the hazard pattern in typical disaster years(1982,2000 and 2007)exhibited obvious spatial heterogeneity due to the uncertainty of meteorological disaster occurrence.(4)Dynamic assessment and zoning of the vulnerability of compound drought and heat stress for soybean in NECBoth drought and compound drought and heat stress were found to reduce the photosynthetic rate,leaf area,and aboveground dry matter mass of soybean,ultimately leading to lower yield.The CROPGRO-Soybean model,with an average relative error of 11.12% or less for yield simulations,was found to be suitable for simulating a large-scale of drought and compound drought and heat stress scenarios for soybean in different maturity groups in NEC.The leaf area index,aboveground dry matter mass,and yield were selected as indicators of disaster damage for the first,second,and third developmental stages of soybean.Spatially,the loss rates for each developmental stage showed a decreasing trend from south to north in NEC,and the loss rates for the compound drought and heat scenario were higher than those for the drought scenario in the same regions,and the vulnerability curves were "S" shaped.The vulnerability of the compound drought and heat stress scenarios was the smallest in the first developmental period(0.096)and the largest in the third developmental period(0.522).Notably,the trend of vulnerability changes at each developmental stage turned around in about 2000,showing an increase to a decrease.Vulnerability was divided into mild,medium,severe,and extremely severe,according to yield loss rates of 50.37%,70.98%,and 85.62%.The proportion of soybean with severe vulnerability at each developmental stage was the highest(34.9%,35.5%,and 37.7%).There was spatial heterogeneity in vulnerability patterns across years,highlighting the degree of impact of extreme weather on soybean yields.(5)Dynamic comprehensive risk assessment and zoning of the of compound drought and heat stress for soybean in NECThe study constructed a dynamic assessment and zoning method for comprehensive risk assessment of compound drought and heat stress in soybean throughout the growth process by coupling multi-source data,crop models,and risk assessment models,taking into account four aspects of disaster risk formation: hazard,vulnerability,exposure,and capacity of disaster prevention and mitigation.The comprehensive risk of compound drought and heat stress in NEC soybean was found to be highest at the third developmental stage(0.454).The comprehensive risk for different developmental stages of soybean reached its highest in the2000 s(2001-2010),and the risk levels were classified based on the quantitative relationship between yield loss rate(same as vulnerability)and risk value.The results showed that comprehensive risk levels exhibited a spatial pattern of high in the south but low in the north,and high in the west but low in the east in NEC.In addition,the risk of soybean production in NEC affected by compound drought and heat stress in recent decades was found to have diminished in the late stage of soybean growth,but remained severe in the early and middle stages.Combining the results of climate suitability and comprehensive risk zoning,the study proposed targeted management and adaptation measures to divide soybean compound drought and heat stress safe production levels.The high,medium,low and safety production levels focused on mitigating the risk and exposure,enhancing disaster prevention and mitigation,and strengthening disaster warning capabilities,respectively.This study addressed the fine-scale dynamic identification and quantitative impact assessment of soybean compound drought and heat stress risk based on multi-source data fusion and multi-model coupling.The study fills the gap in the research foundation for comprehensive risk dynamic assessment of multi-disaster agro-meteorological disaster and improved risk assessment and zoning at the temporal(different years and developmental stages),spatial(4 km× 4 km),varietal(different maturity groups),and disaster types(compound drought and heat)levels.The results of this study not only provide a better understanding of soybean production in NEC but also provide scientific basis for optimal production layout,higher and stability yield,and disaster mitigation reduction and efficiency enhancement of soybean production in NEC.The related technology can also be applied to other disaster species,crops,and regions to promote the development process of dynamic assessment and management of comprehensive risk of compound disasters.