RESEARCH HIGHLIGHT
Climate change and increasing wildfires in the Western US/California
A significant increase in wildfire activity has been observed around the globe, especially in the Western US. The question of to what extent the increase is due to anthropogenic warming or natural variability has raised particular interest. My study combined the results from both observational and modeling and estimated a likely range of anthropogenic contribution (68-88%) to the increase trend of Vapor Pressure Deficit (VPD), a fire weather risk index that is closely linked to warm season burned area.（Zhuang et al. 2021, PNAS (ESI Highly Cited Paper); Turco et al. 2023, PNAS)
Evaporative demand versus precipitation deficit in contributing to Western US drought
The 2020-21 US Southwest drought is a record-breaking event. Our study shows that before the 21st century, drought intensity/coverage was mainly controlled by rainfall variability; however, the contribution of evaporative demand, i.e., potential evapotranspiration (PET), has increased significantly due to anthropogenic warming. This PET impact on drought has already surpassed precipitation for most of the US West and will continue to rise, according to both observation and models. Our results imply the US West is susceptible to more extensive and extreme droughts in the future even with normal precipitation. (Zhuang et al. 2024, Sci. Adv.)
Local/Non-local land-atmospheric interaction and drought
The influence of large-scale oceanic forcing on the US Great Plains (GP) summer drought has been suggested for a long time, yet the underlying mechanisms and role of land-atmospheric interaction are still unclear. We found an inter-seasonal non-local land surface feedback mechanism that potentially links the cold season SST to GP summer drought through spring dryness of the US Southwest (Zhuang et al. 2021, JHM), which can serve as a potential source for seasonal predictability and drought onset. Our another work highlights the significance of lower tropospheric moisture in influencing land-atmospheric coupling and afternoon precipitation in GP under dry soil conditions (Wang et al. 2024, ACP).
Characterizing and quantifying the relationship between atmospheric circulation and surface anomalies
The US Great Plains (GP) is a central part of the global food supply but prone to extreme droughts in history. Earlier studies have identified many factors influencing precipitation and drought here, but the responsible anomalous circulation pattern and thermodynamic condition can vary in different events or areas. I applied the multivariate Self-Organizing Maps (SOM), an unsupervised neural network approach, as well as circulation analogue, to identify a tapestry of large-scale circulation/thermodynamic patterns related to rainfall variability in different parts of GP. Further study of the patterns that were disproportionally responsible for extreme drought can potentially improve understanding and predictability of GP drought (Zhuang et al. 2020, JGRA). Lately I also developed a SOM-Analogue approach that combined the advantages of both SOM and flow analogue (e.g., Zhuang et al. 2021, PNAS) and better quantified the circulation contribution to surface anomalies (Zhuang & Fu 2024, ACP).
Entraining parcel buoyancy model and shallow-to-deep convection transition across climate regimes
Our study Zhuang et al. 2018 (JAS) developed an entraining parcel approach that partitions parcel buoyancy into contributions from different processes (e.g., adiabatic cooling, condensation, freezing, and entrainment). We applied this method to radiosonde profiles from the Atmospheric Radiation Measurement (ARM) program at six sites and evaluated how atmospheric thermodynamic conditions and entrainment influence various physical processes that determine the vertical buoyancy structure across different climate regimes as represented by these sites.
Shallow-to-deep convection transition in the Central Amazon
Editor Highlights for our study Zhuang et al. 2017 (JGRA):
This study examines the role of the diurnal cycle in the transition from shallow to deep convection over the Amazon Basin. The authors found shallow clouds to be more prevalent during the wet season, whereas deep convection was most intense during the transition season. They also found that controlling environmental factors such as Convective Available Potential Energy, convective inhibition, vertical wind shear, and the moist layer very seasonally. This study exemplifies how observations and numerical simulations in combination can provide more insights to physical processes than each alone can.