Future Spatio-Temporal Pattern Of Global Crop Yields And Food Security Assessment Under Climate Change And Human Activities

Human survival requires food as a material basis,but Food and Agriculture Organization of the United Nations（FAO）estimated that more than 800 million people suffer from hunger in the world.As the global population continues to grow with industrialisation and urbanisation,and as diets change,the demand for food increases greatly.It is expected that global crop production will have to double by 2050 to meet human needs.However,with human activities and greenhouse gas emissions,temperatures and CO₂ concentrations are increasing,which will significantly affect the food production.In addition,land use changes caused by climate change and human activities are important impacting factors on global food production.Therefore,it is of great practical and scientific significance to conduct global yield simulation of major crops in the future by combining climate change and land use change,analyze the influencing factors of future crop production changes and assess the balance between food supply and demand in different regions.Many studies have conducted a long and extensive study on the impact of climate change on crop yield,such as the negative impact of temperature increase on crop yield under the RCP scenarios.However,current simulations of future crop yields ignore the impact of future land use changes,which can not be neglected in the simulation.It has led to a lack of adequate understanding of the spatial and temporal characteristics and influencing factors of global future crop production changes.In addition,the balance of food supply and demand in different countries in SSP-RCP scenarios is still poorly understood.In response to the above,the study estimated future global maize,rice,soybean and wheat crop distribution and harvested areas based on future land use changes under different climate change scenarios.Also,based on this data and future climate scenarios,we construct a multi-scenario,long time series global spatial and temporal distribution of crop production coupled with human activities and natural impacts.The study further explored the spatial and temporal trends of global crop production and the contribution of climate change and land use change to production changes.Finally,the global future balance of food supply and demand in different regions was assessed based on the crop productuin.The main findings and conclusions are as follows:（1）This study constructs a global spatial and temporal pattern of multi-crop yields at 10 km resolution at 10-year intervals from 2020 to 2100 based on SSP-RCP scenarios that consider future climate change and human activities.In order to calculate the crop production,the harvested area of new cropland in the future must be estimated in advance.The study innovatively uses the random forest to obtain the future crop harvest area from 2020 to 2100 by recursive simulation based on historical crop harvest area,future climate and land use data and field management data.The results showed that the harvested area of four crops experienced an increasing trend in five SSP-RCP scenarios.However,the trend of the crop area between different scenarios and regions was significantly varied.Because of the uneven distribution of crops,changes in cropland will disproportionately affect the harvested area for one or several kinds of crops.In addition,the future yields of major crops were simulated based on SIMPLE crop model in combination with the harvested area.Comparing with the historical crop yield data,it was found that the yield simulateion were accurate.The range,mean and standard deviation of the simulation yield are close to the observed data.The simulation results can accurately reflect the real yield of the crop.（2）Based on the crop yield simulations,this study analyzed the future crop production change trends and spatial and temporal patterns at the global scale.It is found that the yield trends of maize and wheat show significant variations under different scenarios,rice mainly shows a decreasing trend under all scenarios,while soybean yields basically experienced an increasing trend.However,the yield trends of many crops shift from decreasing to increasing with irrigation increasing,which indicating that field management can effectively change the pattern of climate affects crops in the future.According to the results of Theil-Sen trend analysis and MK test analysis,it was found that the crop production showed an increasing trend in the future.But the trend in boreal shows a significant increase,while it shows decrease in tropical.（3）To examine the impact of future climate and land-use change on crop production,we analysed the impact of climate change,land-use change and their combined effect on production,respectively.To examine the effects of climate factors,we first de-trended the time series data to avoid data self-correlation,then used partial correlation analysis between climate and yield,and counted the number of pixels with both significant climate change and yield change.We found that future crop yields are mainly influenced by changes of solar radiation and temperature.Increases in solar radiation can improve crop yield.Future temperature increases will be beneficial to crops in boreal,but detrimental to those in tropical.And increased precipitation can improve crop yield in the future.However,the dominant climatic influences that affect yield differ between different scenarios.Both solar radiation and temperature have a significant impact on yield in low emission scenario,while temperature is the dominant factor on yield in high emission scenario.The CO₂ fertilisation effect has a significant impact on future global crop yields,which could increase global production by around0.4-2.4 billion tonnes.In addition,the study uses spatial analysis to calculate the impact of land-use change on changes of total production.The results show that the decrease of production mainly caused by the land use change from cropland to forest and grass,while the increase of production mainly attributed to the land use change from shrub and forest to cropland.By 2100,about 13.5%-21.1%of crop production occurs on new cropland,and 6.5%-9.0%of reduction in production caused by cropland loss.The loss in cropland resulted in a 14.8%-21.6%reduction in rice production,which may have impact on people who make rice as their staple food.In addition,urban expand can not be ignored.About 2.5%production loss attributed to urbanization in some scenarios.Meanwhile,the cropland occupied by urban have high quality,and the yield of these cropland is higher than the local mean yield.It can be up to 2.3 times the local mean yield.Spatially,the contributions of climate and land use are similar in the low emissions scenario,while the contribution of climate is higher in the high emissions scenario.However,in terms of impact on total production,climate change leads to a reduction in future production by 1%～10%,while land use change increases the global production by 6%～16%.Land use change dominates production change in most of scenarios（54%to 91%）,except for the SSP5-RCP8.5 scenario（58%for climate）.（4）This study projects future global crop demand,and assesses the balance of food supply and demand in different regions based on the crop production simulated by previous section.The results indicate that about 1 to 3 billion people will face the food shortage from four crop deficits by 2100.The SSP3-7.0 scenario has the highest population growth,resulting in the highest demand for food,and the highest number of people facing food shortages in this scenario.And SSP4-6.0 has the lowest food shortage due to the highest production increase and the lower food demand.Although the increased production from future land use change could meet the demand of170～440 million people,people in Africa,South Asia and Southeast Asia remain also at high risk of food security.The study finds that maintaining crop species and field management could lead to food shortages in many countries with the changing climate and land use.But with adequate water,increased crop production could ease hunger and reduce the people by about 0.9 to 1.3 billion.It reveals that crop species or management practices should be improved in order to reduce the risk of hunger in the future.