陕北地区不同植被改善方案对环境影响的数值模拟

Sensitivity of local weather to different vegetation schemes using meso-scale model (MM5)

植被一直是地气相互作用研究的重点。数值模拟是目前研究植被对大气反馈作用的主要方法。全球和区域气候模式的网格距较大 ,以致于不能真实地描述地表植被覆盖差异 ,因而模拟结果存在一定的不确定性。目前 ,耦合陆面植被模式的中尺度气象模式已成为研究实际的植被建设方案影响天气过程的唯一有效手段。运用中尺度气象模式 MM5 ,模拟了陕北黄土高原地区一次区域性降雨过程及局地环境要素对两种不同的退耕还林方案的敏感性。模式的中心点定于 (37.8°N、1 0 8.8°E) ,模拟区域为(1 0 4 .0 2～ 1 1 3.5 8°E ,33.93～ 4 1 .4 8°N) ,水平分辨率 9km,垂直分层 2 3层 ,时间积分步长 30 s,以美国国家环境预测中心(NCEP)再分析资料作为大尺度背景场。模拟结果表明 ,陕北地区下垫面植被改善后 ,能够使区域降雨的雨带北移 ,降雨量增加 ,降雨过程延长 ,这对于改善陕北地区干旱的气候环境 ,扩展动植物的生存区域具有重要的意义。此外 ,陕北地区植被改善还能够使区域的地表径流减少 ,对于减少黄河输沙量 ,清洁黄河水源 ,保持当地水土具有积极的意义。由于下垫面的变化 ,局地的环境要素也发生了一些相应的变化 :空气湿度增加 ,土壤湿度在短时间内有一定程度的减少 ,长期有增加的趋势 ,气温和土壤温度有一定程度升高 ,

Vegetation plays an important role in land-air interaction. Physically based modeling is an important tool for studying the feedback processes of vegetation to atmosphere. However, it is hard for us to study the effect of different land use on local environments using general climate models (GCMs) and regional climate models (RegCMs) owing to their low resolutions. Meso-scale models have advantages of high resolution, so, coupled with the land surface model, they can be employed to simulate the effect of real vegetation scheme to local weather. In this paper, we use MM5V3 to investigate the sensitivity of local rainfall and environmental conditions to two different vegetation development schemes in northern Shaanxi Province. The domain for simulation is located at (104.02~113.58°E ,33.93 ~41.48°N), centering at (37.8°N,108.8°E), with 9km horizontal resolution. The vertical atmosphere is divided to 23 levels. Time step is 30s. We adopt the reanalysis data from National Centers for Environmental Prediction (NCEP) as the larger scale background weather field. Results indicate that improving the vegetation of northern Shaanxi may shift the local rainbelt northward, increase local precipitation, prolong the rainfall process, which would be good for alleviating the local drought and enlarging the life-form's living space. Furthermore, it can also decrease the surface runoff, and clear the water resource of the Yellow River by holding back the quicksand, which flowing with surface runoff. It is showed that the local environmental conditions would occur some changes accordingly, such as increasing air moisture, air temperature and soil temperature; and decreasing surface temperature and soil moisture, but the soil moisture has showed the increasing tend in the long term. Our research shows that different vegetation schemes may lead to almost uniform variation except for some difference of quantities. The larger the vegetation variation scale is, the more notable these influences are.