Climatic characteristics under the influence of basin-mountain coupled topography and its influence on the ecological restoration of rocky desertification in Mengzi karst graben basin, Southwest China

Clarifying the vertical difference of climate characteristics of karst rocky desertification mountains affected by altitude can help provide a more scientific understanding on the karst mountainous climate and the combined conditions of water and heat, which is of great significance to study on evolution and comprehensive treatment on rocky desertification. In this work, three meteorological observation stations were set up along the basin to the mountainous area in a typical rocky desertification region (Mengzi graben basin area in Yunnan Province) to collect meteorological data in vertical profiles. The vertical climate characteristics and the possible influence on the evolution of rocky desertification were analyzed on monthly and diurnal scale. The results show that: (1) The observation section is the leeward slope for the wind mainly comes from southeast. As a consequence, annual rainfall is the highest on the mountain area (1 027.4 mm), followed by the basin (662.6 mm), and the lowest on the hillside (574.4 mm). The “mountain-valley wind” effect is remarkable, and the valley wind blows during the day, so the rainfall ratio is larger. The topographic fluctuation makes the annual variation coefficient of rainfall in the basin reached 152.36%, which is much larger than the hillside (113.81%) and the mountain (99.36%) and amplified the change of “dry and wet” in the vertical direction. The aridity index shows that the basin is the highest (1.74), the hillside is the second (1.70), and the mountain area is the lowest (0.88). (2) The precipitation difference in the vertical direction makes the annual solar radiation in the mountain area (5 492 MJ·m-2) slightly lower than that of the basin (5 817 MJ·m-2). From basin to the mountain area, the temperature drop rate is of 0.74 per 100 m. There's a big difference in light and heat conditions between the basin and the plateau. (3) The impacts of vertical climate characteristics on ecological restoration of rocky desertification are as follows: concentrated rainfall within the year combining with steep terrain was easy to accelerate soil erosion. Due to less rainfall during the daytime strong evaporation could aggravate the loss of soil moisture and harm the restoration of vegetation. Drought-tolerant crops should be selected in vegetation restoration and treatment because of water shortage in this area. In addition, photothermal crops should be selected in the basin and thermotropic crops should be selected in the mountain area due to the differences in light and heat conditions. In conclusion, selecting species according to local conditions is of great significance to ecological restoration of rocky desertification areas.