基于CERES-Maize模型的玉米水分关键期干旱指数天气保险:以陕西长武为例

Drought Index Insurance of Maize in Water Critical Period Based on CERES-Maize Model:A Case Study of Changwu,Shaanxi

水分关键期干旱是影响玉米生长和产量的主要限制因子,构建此时期玉米干旱损失模型,研究干旱指数天气保险,对于合理设计天气指数保险和解决目前传统农业保险的困境,转移农业气象灾害风险具有重要意义。针对作物特定阶段单因子气象灾害影响难以剥离的问题,本研究在西北农林科技大学旱作农业长武试验站进行了连续3a的雨养玉米观测试验,利用田间试验数据(玉米生长发育数据、气象数据、土壤数据和田间管理数据)对CERES-Maize模型进行参数校正和验证,模拟玉米水分关键期(6月21日-8月31日)干旱对生长和产量的影响,构建干旱损失模型;依据长武1990-2019年的气象数据,利用EasyFit软件筛选出玉米水分关键期干旱指数最优分布模型,模拟干旱发生概率;结合干旱损失模型,利用纯费率精算方法厘定玉米水分关键期干旱指数保险费率;采用投影寻踪的统计方法,设计干旱指数保险赔付方案。结果表明,CERES-Maize模型校正和验证的平均绝对相对误差ARE和相对均方根误差RRMSE都小于10%,符合作物模型模拟精度的要求;模拟的干旱指数(DI)与玉米减产率(y,%)间呈显著的线性函数关系,即y=-0.55DI+107.17;Log-logistic模型对干旱指数分布的拟合精度最高,Anderson-Darling(AD)检验值仅为0.20,轻旱、中旱、重旱和特旱发生的概率分别为9.75%、5.90%、3.71%和3.50%。基于Log-logistic模型厘定的玉米水分关键期干旱指数保险费率为5.6%。在玉米生长水分关键期,干旱指数保险的起赔点为DI=185,DI≤185时,进行分级赔付。

The policy-based agricultural insurance of maize in Shaanxi province was impeded due to its moral hazard,adverse selection and high management cost.Weather index agricultural insurance takes specific meteorological index as trigger which can avoid the defects of the traditional agricultural insurance,and is one of the effective solutions to the current predicament of agricultural insurance.Changwu county located in Shaanxi,an important maize production region,drought stress in the water critical period is the main limiting factor that inhibits maize growth and yield.Therefore,constructing drought stress model for maize in its water critical period and studying the drought index insurance are of great significance for designing the weather index insurance and solving the dilemma of current traditional agricultural insurance.To isolate the influence of a single meteorological factor at a specific crop growth stage,a field experiment of rain-fed maize was conducted in Dryland Agriculture Experiment Station of Northwest A&F University in Changwu from 2011 to 2013.The field experimental data of weather variables,soil,management practices and maize growth and development,were used to calibrate and validate CERES-Maize model.The accumulated precipitation from June 21 to August 31 in Changwu was defined as the drought index(DI)of maize during the water critical period.The DI in 2013 was treated with±20,±40,±60,±80,±100,±120,±140,±160,±180,±200,±220 and±240mm and then distributed daily to simulate the maize yield using CERES-Maize model.The water treatment corresponding to the maximum simulated yield was set as the critical point,and the water treatment less than the critical point was set as the drought treatment.The drought stress model was constructed based on the data of drought treatment and the corresponding simulated yield,in combination with the disaster grade of yield reduction rate,the drought levels and the corresponding drought index thresholds were determined.The optimal distribution model of drought index was selected through EasyFit software using the meteorological data of Changwu from 1990 to 2019,and the occurrence probability of different drought levels in the water critical period of maize were estimated by the selected model.The drought index insurance rate of maize in water critical period was determined by ratemaking method based on the occurrence probability of each drought grade and the corresponding yield reduction rate.The compensation scheme of drought index insurance was designed using the projection pursuit regression method.The results showed that the average absolute relative error(ARE)and relative root mean square error(RRMSE)of CERES-Maize simulation were less than 10%,which was in line with the requirements of crop model simulation accuracy.A linear relationship was showed between maize drought index(DI)during the water critical period and the simulated yield loss(y,%),that was y=-0.55DI+107.17.The Log-logistic model performed best for the drought index distribution,and the Anderson-Darling(AD)test value was only 0.20.The occurrence probability of light,moderate,severe and excessive drought was 9.75%,5.90%,3.71%and 3.50%,respectively.The premium rate of drought index insurance of maize in water critical period was 5.6%.The compensation will start when DI is≤185 and be graded as the maize under drought stress.