中国西南地区石漠化对玉米旱灾风险的影响

为做好喀斯特地区农业旱灾风险防范,揭示石漠化程度对作物旱灾风险的影响机制。该文基于灾害系统理论,引入基于物理过程的农作物模型EPIC(erosion productivity impact calculator),考虑西南喀斯特地貌背景,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,基于此开展不同石漠化程度区玉米旱灾产量的致灾和成灾损失风险评估。结果显示,中国西南喀斯特地区玉米受旱减产的风险呈现从西北到东南增加的趋势。在4种风险水平(2、5、10、20年一遇)下,面积占比最大的产量损失率主要集中分布在0.4~0.5区间内,这主要由地形地势、降水差异和承灾体的脆弱性所共同决定的;受石漠化影响,土层厚度为40 cm时,4种风险水平对应的减产率分别为5.8%、6.1%、7.8%、8.2%;该研究可以为中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重要的科学依据和技术支持。

Impacts of rocky desertification on maize drought risk in Southwest China

Abstract: Frequent drought stress was one of the major factors limiting the crop growth and distribution in the Karst region of Southwest China. In order to prevent the risk of agricultural drought in Karst region and reveal the impact mechanism of rocky desertification degree on the crop drought risk, based on the disaster system theory and the EPIC (erosion productivity impact calculator) crop model, the risk assessment of hazard-inducing factors and disaster loss of maize drought in different areas of rocky desertification was carried out. Taking 1 km grid as the evaluation unit, 2 scenarios were set up in simulation during the period of 1966-2010. The Scenario S1 was completely satisfied with the moisture requirement of maize, the Scenario S2 was completely rain fed, and the other parameters were the same. The difference in maize yield between the 2 scenarios was considered to be the drought loss due to water stress. Considering the Karst topography in Southwest China, taking the accumulated value of water stress during the whole growth period as the hazard-inducing factor, the physical vulnerability curve was simulated with the maize yield loss. The results showed that, in 4 risk levels (once in 2, 5, 10 and 20 years), the yield loss rate with the largest distribution area in Southwest China was mainly distributed in the 0.4-0.5 range. With the increase of annual occurrence rate, the proportion of extreme yield loss risk grade (0.6-1) area accounting for the total maize distribution area was gradually increasing, which was 5.02%, 14.39%, 23.37% and 23.37% at the level of once in 2, 5, 10, and 20 years. Eastern Sichuan, central-eastern Hubei, northern Guizhou, central-southern Guangxi and southern Guangdong reached the loss risk grade higher than 0.5, which was mainly decided by the terrain, precipitation differences and vulnerability of hazard-affected body. Generally when simulating maize production in the Northeast and North China by the crop model, the soil thickness was much larger than the root length of maize. In the Karst area, due to the influence of rocky desertification, the thickness of soil layers of the same soil type was significantly different in space, and the thickness of the soil layer in the serious rocky desertification area was often less than the main root length of maize (40 cm). Under the same rainfall conditions, the time to maintain transpiration for the crops from the field water-holding capacity that the soil can maintain in Karst areas was shorter than the Northeast, North China and other places. The results showed that under different levels of disaster risk, the maize yield loss rate due to soil thickness was quite different. When the soil thickness was 40 cm, the corresponding yield loss rates were 5.8%, 6.1%, 7.8% and 8.2% respectively at the level of once in 2, 5, 10 and 20 years. When the soil thickness was 80 cm, the corresponding yield loss rates were 3.8%, 4.5%, 5.5%, and 6.0%, respectively. Therefore, studying the mechanism of maize yield affected by different soil layer thicknesses was the key to prevent maize drought risk in Karst areas. This research can provide important scientific basis and technical support for agricultural drought disaster reduction and food security of maize regions in Southwest China.