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.