Quantitative Assessment Of Regional Agricultural Drought Risk Based On Experiments And Simulation

With the effect of global warming,urbanization,and water shortage,the influence of agricultural drought hazard has increased significantly.Drought risk assessment is the core content of drought risk management,however,due to the drought formation progress was complex,the theoretical basis and application of drought risk assessment still have the following problems:(1)The criteria definition of drought hazard risk was not unitary.(2)The assessment of drought risk was short of pertinence on the objects,which lack verification.(3)The assessment results cannot reflect the physical formation process of agricultural drought risk.Huaibei Plain of Anhui Province is an important grain production base in China,however,due to the natural and social factors,this region was seriously influenced by the frequent drought hazard.To solve these problems,this study conducted a quantitative evaluation model for regional agricultural drought risk assessment based on the water deficit experiments and crop growing simulation in the Huaibei Plain of Anhui Province.The study included drought-causing-factor identification,drought-affected-body analysis,drought-affected-body sensitivity assessment,and drought loss risk assessment.The main research contents and results are as follows:(1)To identify the severity of drought-causing factors,this study estimated the occurring frequency and analyzed the temporal and spatial distribution characteristics of drought events that occurred during 1955-2012 in the Huaibei Plain of Anhui Province.The drought events were identified by the SPI and CI through run theory,and the joint distribution of drought duration and intensity was calculated based on the Copula function.This study compared and analyzed the identification results of SPI and CI,and then plotted the distribution maps of regional drought characteristics and recurrence periods of drought events.The results showed that the northern cities like Huaibei and Suzhou were the prevalent region with minor drought events(with lower intensity and shorter duration),while the southern cities like Huainan and Bengbu were with moderate drought(with higher intensity and longer duration).Moreover,the drought events frequently occurred in summer(during June-September),which were coincided with the growth period of summer crops(soybean and maize).These research results can provide a reference for regional agricultural drought monitoring work,and provide scientific basis and data support for quantitative assessment of regional agricultural drought risk.(2)To understand the responsive mechanism of crops under drought stress,this study discussed the drought damage sensitivity of crops during different growth stages based on crop water deficit experiments.Soybean water deficit experiments were conducted in 2015 and 2016,and the drought stress levels were simulated by controlling the soil water content during different growth stages.The crop growth indicators and final yield formation under different drought scenarios were compared and analyzed,and the relationship curves between SWD(soil water deficit degree)and the loss rate of crop indicators in each growth stage were established.The results showed that the branching stage was the key period for vegetative growth,during which the drought stress has significant effects on plant leaf development.The flowering and pod-setting stage was the critical period for grain formation,during which the drought stress may lead to lower yield.Moreover,there was a compensation effect after irrigation recovery,and the earlier the recovery,the better the effect.The drought damage sensitivity of different growth stages was as following:flowering and pod-setting stage > pod-filling stage > branching stage > seedling stage.These results can provide a reference for irrigation optimization,and sets the basis for constructing crop drought loss sensitivity curves in the study area.(3)To evaluate the crop drought damage sensitivity quantitatively based on the drought hazard mechanism,this study constructed S-shape crop drought loss sensitivity curves based on field experiments and crop growth simulation.Field observation experiments were conducted in the 2016 and 2017 seasons,and the crop genetic parameters of the DSSAT model were calibrated and verified based on the experiment data.The crop drought loss sensitivity curves during different growth stages were constructed based on the Sigmoid function and different simulated rainfall scenarios.The results showed that the soil water content and evapotranspiration were hysteresis of drought stress.The drought that occurred in the seedling stage may lead to less loss but with a faster development rate,while in the jointing stage,the drought stress may lead to higher loss with a slower rate.Therefore,the drought stress degree during the seedling stage should be noted,and the irrigation level during the jointing stage should be guaranteed.These results could be used for irrigation scheme decision support,and provide a means of realization of drought loss risk curves.(4)On the basis of the above research results,this study constructed a quantitative evaluation model of regional agricultural drought risk assessment.―Drought frequency-crop drought loss-irrigation levels‖ relationship curves and drought risk distribution maps were built based on drought events identification and DSSAT model.The results showed that the western part of the study area had a high loss risk when without irrigation activity.For example,the yield reduction of Bengbu city was more than 80% when there was no irrigation activity,which means the drought-resistant capacity should be improved.However,the yield reduction of all cities were decreased from 34%-56% when with full irrigation,especially in Huainan city.Combined with the drought characteristics of ―long average duration and high severity‖ of Huainan city,irrigation scheme optimization was recommended for local agricultural management.These results can provide references for agricultural drought risk assessment,which is meaningful for improving regional agricultural drought risk management ability.In summary,this study combined crop drought experiments and crop growth model simulation to evaluate the regional agricultural drought risk assessment in the Huaibei Plain of Anhui Province,which helps better understand the agricultural drought formation mechanism and promoted the development of the interdisciplinary field(Disaster,agriculture,and management science).Moreover,this study also supports the development of agricultural production and regional agricultural drought risk management.