我国西南喀斯特山区玉米旱灾风险评估与防范研究

Based on the disaster system theory and the EPIC crop model（Erosion Productivity Impact Calulator）, aiming at the topography characteristics of Southwest Karst mountainous, which is the most prominent area of environmental degradation in China, taking a typical maize varieties as the research object, "regional and growth-staging" risk assessment modes of maize drought disaster are put forward. Under the analysis of "regional vulnerability of different rocky desertification areas", taking the accumulated value of water stress as the hazard-inducing factors, the physical vulnerability curves were simulated with the maize yield loss. Based on this to carry out the "regional" maize drought risk assessment (different rocky desertification areas), the effect mechanism of degree of rocky desertification on maize drought yield loss was explored. Based on analyzing "growth-staging biomass loss varitation", the drought response rules of different maize growth-stages to the thickness of soil layer were revealed. Based on this, the "growth-staging" maize drought risk assessment (different growth-stages) was carried out, the validation field experiment of simulated results were done. According to the effect mechanism of Southwest Karst mountainous topography on maize drought risk, the risk prevention countermeasures of "different regions and growth-stages" were put forward, it can provide scientific base and support for agricultural drought disaster reduction and food security of Southwest China Maize Regions.

本研究基于灾害系统理论，引入基于物理过程的农作物EPIC模型，针对我国环境退化最为突出的地区-西南喀斯特山区的地貌特点，选取典型玉米品种，构建了"分区-分时"玉米旱灾风险评估模型。在分析"不同石漠化区脆弱性差异"的基础上，以水分胁迫累加值作为致灾因子，与玉米产量损失进行脆弱性曲线模拟，基于此开展"分区"（不同石漠化分区）玉米旱灾风险评估，探讨不同石漠化程度对玉米旱灾产量损失的影响机理。在分析"分时生物量损失差异"的基础上，揭示不同生育期玉米生物量对土层厚度的旱灾响应规律，基于此开展"分时"（不同生育期）玉米旱灾风险评估，并对模拟结果进行野外实证。依据喀斯特地貌对玉米旱灾成灾风险的影响机理，提出"分区-分时"的旱灾风险防范对策，为我国第三大玉米主产区-西南山地玉米区的农业灾害预警和保障国家粮食安全提供了重要的科学依据和技术支持。

中国西南地区是世界三大集中连片分布区中面积最大、岩性发育最强烈、生态环境最脆弱的喀斯特连续地带，也是石漠化灾害面积最大、影响最深刻的区域。石漠化是土地生产力下降，土层变薄，地表逐渐呈现类似荒漠景观的土地退化过程。我国西南喀斯特地区由于基岩裸露、土体浅薄、水分下渗等因素，使得该地区水土流失严重，水资源调蓄能力大大降低，一旦遭遇降水不足，极易导致农业旱灾发生。本研究基于EPIC作物模型，研究不同石漠化程度区，同一土壤类型不同土层厚度条件下田间持水量的变化规律，以水分胁迫累加值作为致灾因子，与产量损失进行脆弱性曲线模拟，基于此开展石漠化对玉米旱灾风险的影响研究。结果表明，旱灾致灾指数总体从西北—东南呈阶梯型分布的趋势。旱灾致灾指数≥0.3区域约占93.50%，0.4-0.5区域约占55.78%，0.3-0.4区域约占31.61%，大致分布在四川盆地的东部地区、重庆西北部以及广西、广东省的中部等区域。另外，重度致灾干旱（0.5-0.7）的2个高值区集中分布在湖北省的中东部和广东省南部，约占全国玉米分布区面积的6.10%。这主要与降水系统的异常以及下垫面的地域差异即地形地貌条件有关。四种风险水平下，占西南玉米分布区面积最大的产量损失率值主要分布在0.4-0.5这个区间内。在2年一遇、5年一遇、10年一遇、20年一遇的风险水平下，产量损失率等级（0.4-0.5）的玉米产区占西南玉米总产区的比例分别为55.89%、54.17%、48.99%、44.33%。西南喀斯特地区石漠化分布和玉米旱灾等级分布规律大致相同，表明我国西南地区玉米旱灾风险与石漠化关联密切。本研究可为区域农业旱灾风险防范提供重要的科学依据和技术支持。