Impacts of changes in land cover and topography on a heavy precipitation event in Central Asia

Abstract

Future variations in precipitation due to the effects of topography and possible trends in land-use change in Central Asia are evaluated by utilizing numerical experiments based on a case study. Considering possible changes in land cover, oasification leads to a 0.23 mm increase in regional-averaged precipitation, accounting for 3.0% of the total. Meanwhile, desertification and urbanization decrease precipitation, by about −5.3% and −4.7% proportionally, mainly through changing the near-surface humidity and thermal environment and related upward transport of heat fluxes in the boundary layer. Relatively, varied terrain height produces a more prominent impact on precipitation (up to −13.1% and −24.9% in the 1/2 and 1/4 original terrain height runs), mainly via varying the wind field and microphysical processes (low-level jet and cloud). Furthermore, the heavier rainfall happens over the mountains, while the more sensitive response of precipitation to varied topography and land use occurs over the plains. As the main microphysical conversion pathways of the rainwater budget, the greater peaks of PSMLT (snow melting into raindrops) and PGMLT (graupel melting into raindrops) present over the mountains but not the plains are responsible for the difference in precipitation between the mountains and plains. However, the more sensitive response of plain rainfall might be related to the rapid transit of rainfall over the plains but prolonged mountainous precipitation lasting together with relatively slowly varying microphysical conversion processes when airflows climb the mountains. The findings of this study have important strategic significance for improving the environment of ecosystems and strengthening the capacity for disaster prevention.摘要本研究利用数值试验方法, 定量评估了地形效应和土地利用类型的变化对中亚降水事件的影响. 考虑到可能的地表覆盖变化趋势, 绿洲化, 沙漠化和城市化可改变近地表湿热环境和边界层向上热通量, 导致区域平均降水增加3.0%, 减少5.3%和4.7%; 相对而言, 地形效应对降水的影响更为显著 (1/2和1/4原始地形高度时, 降水减少13.1%和24.9%), 主要影响途径是风场和微物理过程 (低空急流和云) 的变化. 以上研究结果对改善生态环境, 加强防灾能力具有重要战略意义.