Revisiting Biophysical Impacts of Greening on Precipitation Over the Loess Plateau of China Using WRF With Water Vapor Tracers

Abstract

The Loess Plateau is a highland area covering approximately 640,000 km 2 in north central China. Historical longterm deforestation and crop expansion, as well as the semiarid background climate, cause severe soil erosion and land degradation (Fu et al., 2011;He et al., 2006). Moreover, the plateau serves as the ecological safety barrier of the upper reach of the Yellow River. Soil erosion augments the sediment discharge of the Yellow River, increasing the flooding risk in densely populated areas downstream (Fu et al., 2017). To address these issues, China has carried out a series of large-scale ecological programs over the plateau, including the most influential "Grain for Green Program" (GFGP) initiated in 1999 (Bryan et al., 2018). Benefiting from the GFGP, the plateau has shown a significant greening trend since then, with the vegetation fraction increasing from 31.6% in 1999 to 59.6% in 2013 (Chen et al., 2015).Greening is beneficial to soil erosion control and, on the other hand, can influence the terrestrial water balance through biophysical processes (Piao et al., 2020;Zeng et al., 2018). Greening can facilitate surface evapotranspiration due to the larger leaf area, aerodynamically rougher surface and higher canopy conductance for tran-

Greening vegetation cools mean and extreme near-surface air temperature in China

“…Meanwhile, vegetation restoration and conservation in arid/semiarid regions can help to combat land degradation and desertification. However, the cooling effect of greening is achieved at the expense of consuming more terrestrial water in the form of evapotranspiration [59][60][61]. Thus, water resource security also needs to be considered when large-scale revegetation (e.g.…”

Spatial Pattern of Plant Transpiration Over China Constrained by Observations

“…In this regard, the transpiration bias we identified in LSMs may introduce uncertainties in the assessment of the hydrological and temperature effects of vegetation changes. This observation has important ramifications given the backdrop of nationwide ecosystem restoration practices in China, for which growing attention is paid to the biophysical impacts on regional climate, and particularly on water resources, as the associated assessments are largely model‐based (Bai et al., 2020; Li et al., 2018; Liu et al., 2023). It is, therefore, imperative to improve large‐scale estimates of transpiration to aid the robust assessment of afforestation impact on climate in China.…”

Improving Tree Cover Estimation for Sparse Trees Mixed with Herbaceous Vegetation in Drylands Using Texture Features of High-Resolution Imagery

“…The final predictions of the RF model are based on the average of the individual trees generated from bootstrap samples [38]; hence, RF predictions may tend to be biased toward the mean. (5) The image spatial scales do not entirely match. The mismatch in spatial scales between the resampled image pixels and the Landsat 8 remote sensing image pixels introduces errors in extracting different resolution texture features.…”

“…In order to alleviate the deteriorating ecological environment and soil erosion, the government began to implement ecological restoration projects such as returning farmland to forest and grassland and closing mountains to grazing in 1999 to accelerate the restoration of forest and grass vegetation on the Loess Plateau [3,4]. Due to vegetation restoration in recent years [5], it has been possible to study the vegetation coverage in the Loess Plateau region.…”