Drought Risk Assessment For Maize In The United States Under Global Change Scenarios

Global climate change is the main trend and feature of the global climate in the past century.In terms of extreme precipitation events,drought events have shown a statistically significant increase trend in the continental United States(CONUS),which poses a huge challenge to the production of maize in the United States.As the world's largest maize planting and exporting country,quantitative evaluation of the drought exposure,vulnerability and risk loss of maize in the United States will help to better fortify and manage future drought disasters in the United States,thereby reducing U.S.maize production risks and safeguarding food security.According to the regional disaster system theory,this study started from the hazard factor and the hazard-bearing body,and analyzed different scenarios(RCP4.5-SSP2,RCP8.5-SSP3)and different periods(historical period: 1986-2005;near-term: 2016-2035;mid-future: 2046-2065),to comprehensive assess maize drought risk from three aspects: drought exposure,drought vulnerability,and drought risk loss.The hazard factor is the drought frequency calculated by the Palmer drought index;the hazardbearing body is the distribution of maize planting estimated by Max Ent model and redistribution method;the drought exposure is obtained by the superposition of the hazard-bearing body and the hazard factor;the drought vulnerability is mainly constructed by the EPIC model;and the drought risk loss is mainly simulated by the EPIC model.Thus,A "multi-scenario,multi-period,and multi-dimensional" crop drought risk assessment method was formed.This paper drew the following conclusions:(1)From the spatial perspective,the drought frequency in the U.S.maize growing period shows a pattern of high in the eastern and western CONUS and low in the central CONUS;from the temporal perspective,it showed a trend of decreasing in the nearterm and increasing in the mid-term.In each period,the drought frequency in the eastern and western CONUS was about 10%-15% higher than that in the central CONUS.The drought frequency in the near-term will decrease by about 10% compared with the historical period,and the highest drought frequency will not exceed 35%.The distribution of high-value areas of drought frequency during the maize growth period in CONUS is staggered from the distribution of high-density areas of maize planting in CONUS.This kind of hazard disaster and hazard-bearing bodys are spatially staggered,avoiding the impact of high intensity hazard disaster on high-density hazard-bearing body.(2)In the future,the distribution of maize planting in CONUS may move to the south,and the overall distribution pattern is consistent with the historical period.In near-term,due to the decrease in the frequency of droughts,a large-scale north-south non-exposed area will appear in the central and western Central Plains.The eastern maize planting is mainly concentrated in the maize belt in the northern part of the Central Plain,and it shows a clear southward trend compared with the historical period.The secondary major maize planting areas will mainly be the northeastern CONUS and the Atlantic coastal plain in the future.Compared with the near-term,the high-density maize planting area will be larger in the mid-term.In terms of exposure area composition,the future U.S.maize drought exposure area is mainly from grids of 1000-2500 million hectares,followed by grids larger than 2500 million hectares or grids of500-1000 million hectares.From the perspective of drought exposure intensity,the drought exposure intensity of maize in the mid-term is mainly the drought frequency of more than 30%,and the drought exposure intensity of maize in the near-term is mainly the drought frequency of less than 25%.(3)The drought vulnerability curve of maize is dominated by "S" and "J" types.Generally,the vulnerability corresponding to the "S" type curve is larger than that of the "J" type curve.There are clear spatial differences in maize drought vulnerability in CONUS.The starting point of the rapid growth of the maize drought vulnerability curve in CONUS is mainly below 0.4.Generally,the starting point of rapid loss growth in the east is low(overall Di1<0.4),and the starting point of rapid loss growth in the west is high(overall Di1>0.4).In CONUS,the inflection point of rapid loss growth in the drought vulnerability curve in the maize growth period of is in the range of 0.3-0.6.Generally,the inflection point of rapid loss growth in the east is low(the overall Di2 is between 0.3 and 0.4),and the inflection point of rapid loss growth in the west is high(Overall Di2>0.4).The end point Di3 of the rapid growth of the maize drought vulnerability curve in CONUS is greater than 0.4,and the difference between east and west is not obvious.The cumulative loss rate of CLr during the growing period of maize in CONUS was greater than 40%,and the cumulative loss rate of maize during the growing period in the northeastern CONUS(CLr>50%)was generally higher than that in the southwest(CLr was between 40% and 50%).(4)In the future risk of maize drought in CONUS,the rate of maize drought yield loss is inconsistent with the spatial distribution of drought yield loss.The drought risk loss in the United States in the mid-term will be significantly higher than that in the near-term,and compared with the historical period,except for the northern Central Plains,the risk of maize drought in CONUS will increase to varying degrees.South Dakota and Texas will see the most severe maize drought risk losses in mid-term.Although maize-producing states such as Indiana and Ohio have larger maize acreage,due to the low rate of maize drought losses in the states,maize drought yield losses did not exceed 1,000 kilotons in each period.Although Texas has less maize acreage than Illinois and other large maize-producing states,due to the high rate of maize drought loss,maize drought will lose nearly 4,000 kilotons of yield in the future period.