Vegetation greening accelerated the propagation from meteorological to soil droughts in the Loess Plateau from a three-dimensional perspective

Investigating the propagation from meteorological drought to hydrological and soil droughts is critical for drought early warning and forecasting. Vegetation is a main factor affecting drought propagation process. However, how the changing vegetation cover affects the drought propagation, especially over semiarid regions with strong coupling between drought and vegetation, remains unknown. Moreover, existing studies are often analyzed in lower dimensions, ignoring the nature of the evolution of droughts over space and time simultaneously. Focusing on the Loess Plateau with significant greening due to the implementation of vegetation restoration programs and climate warming, this study identifies the characteristics of the three types of droughts and their propagations from a three-dimensional perspective. Two sensitivity experiments based on a highresolution land surface model, driven by static and dynamic leaf area index (LAI), are conducted to investigate the impact of vegetation greening during 2001-2021. The results show that vegetation greening has significantly exacerbated soil droughts and accelerated the propagation from meteorological to soil droughts via transpiration that directly consumes soil water. However, the impact of greening on hydrological droughts is relatively smaller. Specifically, vegetation greening has increased the duration, affected area and severity of soil droughts by approximately 5 months (38 %), 84 % and 98 % respectively. Meanwhile, the greening has shortened the propagation time from meteorological to soil droughts by 0.47 months, and increased the propagation probability by 17 %. In addition, more soil drought events are likely to migrate eastward and the drought migration distance is increased by 139 % under vegetation greening. This study provides new insights into the impact of greening on drought propagations from a three-dimensional perspective and highlights greater impact on soil droughts over the Loess Plateau.