Yongqiang Liu

Future wildfire trends under changing climate Climate models have projected significant climate change for this century due to the greenhouse effect, including an overall increase in temperature worldwide and a drying trend in some regions. Thus, it is likely that wildfire would increase in many regions. Meanwhile, the warming and drying trends would increase safety risk for prescribed fire. This study understands climate-fire relationships and projects future wildfires for the development of mitigation strategies. The objectives include understanding fire-weather relationships based on historical data, developing fire projection models using statistical and dynamical tools, and projecting future global, regional, and local wildfire trends, the impacts of changing fire and fuel conditions on fire emissions and smoke transport, and prescribed fire safety risk and windows.

Seasonal wildfire variability Wildfire activity of a fire season varies dramatically from one year to another. Seasonal prediction of wildfires is needed for fire management to plan and implement fire prevention and mitigation. This study investigates atmosphere-wildfire interactions to improve seasonal prediction skills of regional and global wildfires. The objectives include identifying atmospheric factors for seasonal wildfire variability, understanding the local and remote impacts of atmospheric circulation patterns and ocean conditions on wildfires, and developing and applying seasonal wildfire prediction models.

Smoke dynamics Smoke plume dynamic science focuses on understanding the various smoke processes that control the movement and mixing of smoke. An improved scientific understanding of smoke plume dynamics will allow for more accurate assessments and predictions of the fate and impacts of wildland fire emissions. This study is focused on smoke plume rise, the height of smoke plume. This property determines how far smoke can be transported to affect air quality in downwind direction and is required as an initial condition in many regional air quality models. The objectives include measuring smoke plumes from experimental fires in the Southeast and other US regions, developing smoke plume rise models, and simulating and predicting smoke plume processes and interactions with the atmosphere, fire behavior, and fuel.

Air quality and human health impacts of smoke Wildfires emit large amounts of pollutant particles and gases. Fire emissions accounted for approximately one-third of the total emissions of PM2.5 in the US. The fire emissions of O3 precursors such as volatile organic compounds and NOx can elevate tropospheric O3 level. PM2.5 and O3 pose severe threats to air quality and human health and are two of the air pollutants subject to the US Environmental Protection Agency’s National Ambient Air Quality Standards. This study estimates emissions from wildfires and prescribed fires in the Southeast and the CONUS and evaluates the air quality and human health impacts. The objectives include developing fire detection algorithms, measuring fuel conditions, estimating fire emissions, developing regional air quality modeling tools, and simulating the local and regional air quality and human health impacts of wildland fires.

Roles of wildfire in climate and hydrological variability This study simulated radiative and climatic responses to biomass burning in the Amazon region, simulated the climate impacts of the 1988 Yellowstone wildfires, developed a theoretical model based on atmospheric fluid dynamics to investigate interactions between wildfires and the Santa Ana winds, detected fire induced vegetation changes in the US, and analyzed impacts of wildland fires on water resources in the CONUS. The results show that wildfires can feedback climate by modifying surface water and heat fluxes and increasing atmospheric stability, and delaying monsoon onset, the 1988 Yellowstone wildfires could have enhanced the drought by creating the anticyclonic circulations trend and reducing precipitation, wildfires in southern California can intensify the Santa Ana winds, and large wildfires reduce vegetation coverage, increase surface albedo, leading to increased temperature and reduced humidity, and more annual river flow in the western regions.

The climate and hydrologic effects of afforestation This study simulated the hydroclimatic impacts of the Green Great Wall (GGW) project in North China and the conversion from farmland to forests in the Southeast US in the early 1900s, compared the impacts of afforestation between dry and wet conditions, investigated the remote role of ocean conditions, and analyzed the roles of vegetation in affecting future drought trends. The results show that the GGW is likely to improve overall hydroclimate conditions by increasing precipitation and reducing prevailing winds and air temperature, overall precipitation decreases in July and increases in January in the restoration region of the Southeast in response to the forest restoration, afforestation would modulate hydrological cycles by reducing evapotranspiration on clear days and elevating it on rainy days, a significant hydrologic response to afforestation only occurs if ocean temperatures are allowed to vary and the oceanic source of moisture to the continent is enhanced, and future droughts would increase more significantly on forest lands (grasslands) than the corresponding farmlands (drylands) in warm and moist/dry climate regimes.

Land-atmosphere interactions This study developed coupled systems based on linearized soil and air energy and water conservation equations with analytical solutions to obtain time scales of land-air interactions, analyzed global distributions of time scales of the air-land disturbances, simulated land breeze with a three-dimensional large-eddy model, analyzed major processes for the formation of shallow convective clouds induced by land breeze, and developed a parameterization scheme. The results show that the air-land system includes time scales from daily to seasonal, the air-land interactions increase the seasonal time scale from about one to three seasons, the interactions with soil water are the most important factor for scale length, and land-surface heterogeneity can generate local and mesoscale circulations, which can further modify land-surface heat and water exchanges and clouds.

My research is focused on climate-forest ecosystem interactions. It is aimed at understanding forest disturbances (wildfire, land cover change, and forest water stress), their interactions with climate variability and climate change, and the environmental consequences. The combined approach of field measurements, numerical modeing, and theoretical and statistical analyses is used to investigate the processes, mechanisms, and impascts of the disturbances and to develop evaluation and prediction techniques. This research is expected to help strategy development and implementation to reduce forest vulnerability to forest disturbances and their adverse environmental impacts.

Wildfire is a natural process with many ecological benefits. However, wildfire and smoke damage trees, properties and human life, adversely affect air quality and human health, and modify regional and global climate. The impacts are getting more severe under the changing climate due to the greenhouse effect. On the other hand, the increasing concerns about the air quality and safety under warmer and drier conditions limit the capacity in implementing prescribed fires, which are extensively used as a forest management tool to maintain forest health and reduce wildfire risk.

My research on fire-smoke-atmospheric interactions improves understanding and quantification of wildfire regimes, smoke dynamics, and the relationships with atmospheric conditions, provides scientific foundations for developing analysis, simulation, and prediction tools to evaluate fire and smoke impacts, and aids managers and policymakers to develop strategies for better implementing forest management tools and reducing vulnerability of forest ecosystems, society, and the public to wildfire disturbance, smoke hazard, and climate change/variability.