GEOGRAPHY

How the regional climate affects the return of farmland to forests (grasslands) on the Loess Plateau


Schematic diagram of the influence mechanism of large-scale vegetation construction on regional temperature on the Loess Plateau. Courtesy of the research group

Schematic diagram of the impact mechanism of large-scale vegetation construction on regional atmospheric water circulation on the Loess Plateau. Courtesy of the research group

Recently, the team of Tian Leihe, a young researcher at the Yellow River Basin Green Development Research Institute of Lanzhou University, and Professor Zhang Baoqing carried out numerical simulation of the hydrology and climate of the Loess Plateau, which systematically elucidated the response mechanism of regional climate to the project of returning farmland to forests (grasslands) on the Loess Plateau, and the relevant results were published online in the Journal of Geophysical Research: Atmosphere.

The Loess Plateau, located in the middle reaches of the Yellow River Basin, plays a very important role in China’s economic and social development and ecological security. Since the implementation of the project of returning farmland to forests (grasslands) in the 1990s, a large number of slope arable land has been converted into grassland and woodland, the level of regional vegetation cover has been significantly improved, and the amount of yellow sediment has been greatly reduced. Vegetation construction can have an impact on the hydroclimatic processes of the Loess Plateau by changing land use types, vegetation cover and surface albedo. Studies have shown that the project has caused a sharp increase in regional evapotranspiration water consumption, consuming already limited water resources, resulting in a sharp decline in the yellow runoff and exacerbating the regional drought and water shortage. However, these existing conclusions only consider the hydrological effects of the land surface in a one-way manner, ignoring the feedback effect of regional climate. When assessing the impact of large-scale vegetation construction, it is necessary to consider the two-way effect between land surface and atmosphere at the same time, but at present, the feedback effect of large-scale vegetation construction on regional temperature and precipitation on the Loess Plateau is not clear, and the impact of large-scale vegetation construction on regional climate needs to be answered urgently.

Based on the coupling model of land and air, multi-source remote sensing observation data and climate reanalysis data, the impact of large-scale vegetation construction on regional temperature, precipitation, water vapor transmission and water vapor-precipitation conversion was quantitatively evaluated, and the following two scientific understandings were mainly obtained.

First, the greening of vegetation caused by large-scale vegetation construction leads to a significant decrease in albedo, which leads to an increase in net short-wave radiation, which in turn leads to an increase in the sensible heat flux. Although the latent heat flux also increased significantly, at the interannual scale, the energy process changes caused by radiation are stronger than the energy process changes caused by non-radiation (evapotranspiration), which eventually makes vegetation construction show a warming effect on the Loess Plateau on an annual scale.

Second, large-scale vegetation construction significantly increases regional evapotranspiration, makes the near-surface atmosphere more humid, enhances the positive feedback between soil moisture- vegetation and precipitation, leads to stronger water vapor radiation and increased cloud cover, improves the precipitation recycling rate, and strengthens the regional atmospheric water cycle, and finally makes vegetation construction have a positive effect on the increase of precipitation on the Loess Plateau.

This research work provides a new perspective for understanding the regional climatic effects of vegetation construction on the Loess Plateau, which is conducive to in-depth understanding of the impact of afforestation on regional climate, has important academic value for exploring the interaction between human activities and climate, and has important theoretical and practical significance for the ecological protection and high-quality development of the Yellow River Basin, as well as the sustainable management of vegetation restoration and reconstruction. (Source: China Science Daily Wen Caifei Faisa)

Related paper information:https://doi.org/10.1029/2022JD036738



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