Large-Scale Afforestation Enhances Precipitation by Intensifying the Atmospheric Water Cycle Over the Chinese Loess Plateau

Afforestation is an appropriate approach to control soil erosion, but consumes extra water resources. It also exerts feedbacks on local precipitation, affecting the water availability for water-limited areas. The Chinese Loess Plateau (LP) has implemented the world's largest afforestation program to mitigate severe soil erosion. However, it remains unclear how the atmospheric water cycle responds to large-scale afforestation under climate change. Here we show that afforestation elevates precipitation in rainy season by intensifying the atmospheric water cycle over the LP. Results show the upward trend of vegetation coverage fraction increased by 3.15% decade(-1) and climatological precipitation increased by 54.62 mm after launching the large-scale afforestation in 1999. Such afforestation also enhanced evapotranspiration by 22.56 mm. We found the moisture inflow and outflow continuously decreased, but more atmospheric moisture was retained since the rate of decline of inflow was less than that of outflow. Using a dynamic precipitation recycling method, we explored changes in precipitation recycling and components of the atmospheric water budget. The precipitation recycling ratio increased from 9.16 +/- 0.35 to 10.18 +/- 0.28% after the afforestation. Both external and internal branches of the atmospheric water cycle have been strengthened, and their contributions to the increased precipitation are 84.93% and 15.07%, respectively. The afforestation caused a more humid atmosphere, heightened soil moisture-vegetation-precipitation feedback, stronger moisture convergence, and more clouds; these changes favored precipitation generation. This study advances the understanding of how afforestation affects regional climate from a precipitation recycling perspective, further assisting decision-makers to establish sustainable afforestation strategies.

Automated summary

Afforestation is an effective method to control soil erosion, but it consumes water resources and has feedback effects on local precipitation. The world's largest afforestation program in China has increased precipitation and strengthened the atmospheric water cycle on the Loess Plateau. Afforestation has created a more humid atmosphere, enhanced the soil moisture-vegetation-precipitation feedback, and favored precipitation generation.