基于机器学习和未来气候变化模式的埃塞俄比亚粮食产量预测

Crop yield prediction in Ethiopia based on machine learning under future climate scenarios

  • 摘要: 对于以农业产业为支柱的埃塞俄比亚, 粮食供应和安全对国家安全和人民的生计尤为重要。由于作物生长和气候因素之间的复杂耦合关系, 预测气候变化对农作物产量影响具有较大难度, 机器学习技术为这种复杂系统变化的预测提供了一种有效途径。本研究利用37个全球气候模式(GCM)的数据以及土壤数据, 基于机器学习模型, 预测了埃塞俄比亚2021年至2050年5种主要粮食作物在SSP1-2.6、SSP2-4.5和SSP5-8.5情景下的产量变化。经GCM和变量的筛选后, 利用梅赫季和贝尔格季中5种主要粮食作物的10个产量数据对直方图梯度提升决策树、极端梯度提升随机森林、轻梯度提升决策树、随机森林、极限树以及K近邻6种机器学习模型进行训练。经过模型评估, 选择表现良好的3个模型, 采用线性回归算法进行堆叠, 然后使用堆叠模型进行预测。研究结果表明, 未来30年埃塞俄比亚梅赫季5种主要粮食作物产量变化以增产<2 t·hm−2为主; SSP126情景下的贝尔格季将出现更明显的减产现象, 这可能是由于温室效应的减缓降低了CO2的施肥效应。随着人类活动造成的生态环境恶化, 研究区农业生产对粮食结构改变和重新分配生产力的需求不断增长, 导致农作物生产力向新的适宜地区转移。研究区在SSP126和SSP585情景下将分别因为干旱缓解和温室效应加剧而获得更高的粮食作物生产力。

     

    Abstract: Crop yield and agricultural development are the foundation of human survival. In Ethiopia, where agriculture is the economic backbone, food supply and security are crucial for national security and people’s livelihoods. Crop yield is greatly influenced by climatic conditions, but the coupling relationship between them has not been clearly explained, which poses difficulties for quantitatively analyzing crop yields under climate change. The development of machine learning techniques provides a method for predicting changes in such complex systems. This study predicts the changes in the yield of five major staple crops in Ethiopia from 2021 to 2050 by using machine learning methods combined with climate predictions from Global Climate Models (GCMs) under different future scenarios in the Sixth Coupled Model Intercomparison Project (CMIP6). Data on 9 climate variables from 37 GCMs under four scenarios (i.e., historical, SSP1-2.6, SSP2-4.5 and SSP5-8.5) in CMIP6 were obtained. A Taylor diagram was used to select the best-performing GCMs and calculate their weighted averages. These averages were combined with five soil indicators to form an independent variable database. After removing highly correlated variables using Spearman’s correlation coefficient, machine learning models were trained using 10 yield data variables of teff, maize, wheat, barley and sorghum for two major growing seasons in Ethiopia from 1995 to 2020 as dependent variables. This paper employed histogram gradient boosting (HGB), extreme gradient boosting random forest (XGBRF), light gradient boosting machine (LGBM), random forest (RF), extra trees (ET) and K-neighbors as machine learning models. After model evaluation, the top-performing three models were stacked using linear regression. The independent variables were input into the final model to predict the yields of the 5 main staple crops in Ethiopia from 2021 to 2050. The results were analyzed, and the following conclusions were drawn. 1) CMCC-CM2-SR5, MPI-ESM1-2-LR, EC-Earth3-Veg-LR, EC-Earth3-Veg and MPI-ESM1-2-HR obtained higher overall scores in the Taylor diagram analysis, indicating better simulation of climate in Ethiopia compared to other GCMs. 2) The coefficient of determination (R2), mean absolute error (MAE), and explained variance score (EVS) of the XGBRF, RF and ET were higher than those of HGB, LGBM and K-neighbors. The stacking method of ensemble learning improved the performance of the ensemble model over individual models. 3) Over the next 30 years, the changes in crop yield during the Meher season (the longer growing season in Ethiopia, which is generally from April to December) were mainly within 2 t·hm−2. In the Belg season (the shorter growing season in Ethiopia, which is generally from February to September), there was a greater decrease in yield under SSP126 scenario, while the other two scenarios showed an increase, possibly due to the mitigation of greenhouse effects reducing the fertilization effect of CO2. 4) With intensification of social conflicts and environmental degradation caused by human activities, there is a growing need in the research area to change the agricultural structure and redistribute productivity, and this leads to the transfer of agricultural productivity to new suitable areas. Under SSP126 and SSP585 scenarios, the research area will achieve higher crop productivity due to the alleviation of drought conditions and the exacerbation of greenhouse effects, respectively. Results of this study demonstrate the changes in crop yield in the research area under different future climate change scenarios, providing references for determining agricultural production potential and formulating agricultural policies in the research area.

     

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