Evaluation Of The Impact Of Spatial And Temporal Evolution Of Drought On Maize Growth And Yield

Drought has always been one of the most threatening natural disasters in the world.Drought will cause serious losses to China’s food production and national economy,thus affecting the stable development of the country.Maize is one of the three major food crops in China.More than 70%of the planting area of maize in China is threatened by drought,resulting in more than 1500×10⁴t yield losses every year.Analyzing the impact of drought on maize production under the background of climate change has reference significance for relevant agricultural departments to formulate effective drought response measures to meet the increasing food demand under the background of future population growth.In this paper,Firstly,referring to climate zoning and agricultural zoning,the maize planting sites in this study area are divided into northwest desert area（sub-region I）,North China humid and semi humid warm zone area（sub-region II）and northeast humid and semi humid warm zone area（sub-region III）;Secondly,based on the meteorological drought index（SPEI）and agricultural drought index（SMDI）,combined with the GCM data in CMIP6,this paper analyzes the temporal and spatial evolution of agricultural drought and meteorological drought in each sub-regions at various timescales during the growth period of spring/Summer maize in the study area in the historical period（1961～2018）and the future period（2021～2100）under SSP1-2.6,SSP2-4.5,SSP3-7.0 and SSP5-8.5 scenarios;Then,the genetic coefficients of maize in DSSAT-CERES-Maize model were calibrated and verified through the measured maize phenological period and yield data,then,the DSSAT-CERES-Maize model was used to simulate the key growth period,maximum LAI_max,aboveground biomass and yield in the historical and future periods to analyze the variation characteristics of maize growth and yield;Finally,through the correlation between drought index and maize yield related factors,the impact of drought on maize growth and yield during maize growth period is analyzed,and the key months,key time scales and the most suitable drought index are explored.The main conclusions are as follows:（1）The temporal and spatial variation characteristics of agricultural drought and meteorological drought in maize growth period are different in each sub-region.In the historical period（1961-2018）,in the sub-region I and the sub-region II,the agricultural drought degree at the depth of 10-40 cm soil layer is higher than that at the depth of 0-10 cm soil layer.In the sub-region III,the severity of agricultural drought at the depth of 0-10 cm and10-40 cm soil layer is similar;During the growth period of maize,the severity of meteorological drought changes greatly,and there are more alternations of dry and wet;The severity of agricultural drought in maize growth period changes slightly,and usually presents a consistent agricultural dry and wet state in the whole growth period.In the future period（2021-2100）,under the scenarios of SSP1-2.6,SSP2-4.5,SSP3-7.0 and SSP5-8.5,the frequency of meteorological drought in July,August and September during the growth period of maize in the sub-region II will decrease;Under the scenarios of SSP1-2.6 and SSP2-4.5 in the future,the agricultural dry and wet state of 0-10 cm depth soil layer and 10-40 cm depth soil layer in the three sub-regions is basically the same,the severity of agricultural drought in10-40 cm depth is higher than that in 0-10 cm depth,there are many inter annual dry and wet alternations between 2021 and 2060,and the severity of agricultural drought is not high,the frequency of agricultural drought will increase from 2061 to 2100;Under the scenarios of SSP3-7.0 and SSP5-8.5 during 2021-2040,the agricultural dry and wet state of 0-10 cm depth soil layer and 10-40 cm depth soil layer in three sub-regions is inconsistent,when the agricultural drought occurs in 0-10 cm soil layer,the 10-40 cm soil layer is in a normal or relatively wet state,during 2021-2070,the 0-10 cm depth soil layer will be in an agricultural drought state for a long time,After 2065,the frequency of agricultural drought in 10-40 cm depth soil layer will increase;Under SSP5-8.5 scenario,0-10cm soil depth will be in the state of agricultural drought for a long time from 2021 to 2070,and there will be continuous extreme agricultural drought about every 20 years.（2）The growth and yield of spring maize and summer maize show differentchanges in historical period and future period.DSSAT-CERES-Maize model can well simulate the growth and yield of spring maize and summer maize.The R² of observed and measured values is greater than 0.72,and the RRMSE is about 15%（less than 20%）.The simulation effect of DSSAT Ceres Maize model on Maize phenology is better than that of yield.In the historical period,the maximum LAI_max of spring maize in the sub-region II and the sub-region III was higher than that in the sub-region I;The aboveground biomass of spring maize in the three sub-regions was similar at maturity;From 1961 to 2018,the yield of spring maize and summer maize in each region showed a slight downward trend;The maximum LAI_max,aboveground biomass and yield of spring maize were higher than those of summer maize.In the future,there will be little difference in the key growth period,maximum LAI_max,aboveground biomass and yield of maize under SSP1-2.6,SSP2-4.5,SSP3-7.0 and SSP5-8.5scenarios from 2021 to 2060,and great difference from 2061 to 2100;The anthesis and maturity of spring maize will be advanced,the yield of spring maize has a downward trend under SSP1-2.6,SSP2-4.5,SSP3-7.0 and SSP5-8.5 scenarios;The anthesis period and maturity period of summer maize will be postponed,especially in 2021-2060;From 2021 to2060,the yield of summer maize has an upward trend under the scenarios of SSP1-2.6,SSP2-4.5,SSP3-7.0 and SSP5-8.5,and decreases from 2061 to 2100.（3）Drought has different effects on spring maize and summer maize.The correlation between maize growth and yield and meteorological drought index（Standardized Precipitation Evapotranspiration Index,SPEI）is better than agricultural drought index（Soil moisture deficit index,SMDI）;The effect of agricultural drought on maize growth and yield lags behind that of meteorological drought;The linear slope of drought index had the best correlation with the linear slope of spring maize yield,while the linear slope of drought index had the best correlation with the linear slope of the maximum LAI_max in the growth period of summer maize;For summer maize,drought had the greatest effect on yield before and after anthesis（July to August）;SPEI in August and four months in three sub-regions can better identify the meteorological drought in the growth period of maize.The Key months and timescales with the highest positive correlation between drought indicators(SPEI,SMDI_0-10 and SMDI_10-40)and maize yield related elements(maximum LAI_max in growth period,aboveground biomass at maturity and yield)under SSP1-2.6,SSP2-4.5,SSP3-7.0 and SSP5-8.5 scenarios in the future are similar to those in the historical period.In the future,the yield of spring maize has an obvious downward trend under various scenarios.Spring maize varieties should be improved to adapt to the climate change in the future;In the subsequent agricultural production process,SPEI at 4-month timescale in August can be used to effectively identify the drought in the growth period of spring maize,and DSSAT-CERES-Maize model can be used to predict the trend of maize yield,so that relevant agricultural departments can formulate Countermeasures in advance.