2013 Progress Report: Response of Regional Air Quality to Severe Drought

EPA Grant Number: R835191
Title: Response of Regional Air Quality to Severe Drought
Investigators: Allen, David T. , Huang, Ling , Kimura, Yosuke , McDonald-Buller, Elena , McGaughey, Gary , Zheng, Jeff
Institution: The University of Texas at Austin
EPA Project Officer: Chung, Serena
Project Period: June 1, 2012 through May 31, 2015 (Extended to May 31, 2016)
Project Period Covered by this Report: June 1, 2013 through August 31,2014
Project Amount: $750,000
RFA: Extreme Event Impacts on Air Quality and Water Quality with a Changing Global Climate (2011) RFA Text |  Recipients Lists
Research Category: Air Quality and Air Toxics , Global Climate Change , Water and Watersheds , Climate Change , Air , Water


In recent years, the effects of drought in Texas have been among the most severe in the southern United States. Most climate models suggest that droughts will become more frequent in the future in response to increased concentrations of greenhouse gases and other radiative forcing species in the atmosphere. Drought-induced changes in natural and anthropogenically managed and cultivated land cover systems have the potential to affect regional air quality. The implications of these effects are important to understand as Texas concurrently faces requirements to achieve or maintain attainment with the National Ambient Air Quality Standards (NAAQS) for ozone and fine particulate matter in several large metropolitan areas. This work characterizes land cover for eastern Texas climate regions, explores the variability in meteorological conditions, biogenic emissions, and dry deposition rates during years with severe to exceptional drought conditions as well as years with average to above average precipitation patterns, and assesses the effects on predictions of Texas air quality.

Progress Summary:

Annual biogenic emissions in Texas ranked first within the continental United States in the 2011 National Emission Inventory. Recognition of the roles of biogenic volatile organic compounds in tropospheric ozone and organic aerosol formation has been critical for air quality planning efforts in the state. This research has investigated the interannual variability in leaf area index derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) and isoprene and monoterpene emissions estimates from Model of Emissions of Gases and Aerosols from Nature (MEGAN) in four eastern Texas climate regions with diverse climatology and land cover shown in Figure 1. The analyses focused on the time period of 2006-2011, years with recurring extreme to exceptional drought (2006 and 2011) and average to above average precipitation patterns (2007).
Figure 1: Thirty-six land cover/land use types in eastern Texas (Source: Popescu et al., 2011) with boundaries of Texas climate divisions (Source: National Oceanic and Atmospheric Administration). Developed metropolitan areas are shown in red. Dallas and Fort Worth are located in North Central Texas, Austin and San Antonio in South Central Texas, and Houston in the Upper Coast.
Interannual variability of LAI in climate regions with low-growing vegetation was greater than in more heavily forested areas and exceeded 20%, with reductions of LAI exceeding 0.5 m2/m2 in drought years. Maximum interannual variability in estimated monthly isoprene emissions exceeded 30%. Estimates of isoprene and monoterpene emissions in the two central regions were lower by as much as -24% due to significant reductions of LAI during droughts in 2006 and 2011. Estimates of isoprene and monoterpene emissions were influenced by potentially competing effects of LAI and meteorological fields, such as temperature and solar insolation, during drought years. As efforts to examine the effects of drought on vegetation health and mortality in Texas and other information are incorporated into a better understanding of land cover change in the future, it will be important to consider the effects on biogenic emissions.
In MEGAN, the adjustment to emissions from a standardized set of environmental conditions is determined using a multiplication of individual activity factors for leaf age, soil moisture, and the canopy environment. This work also quantified the variability of environmental inputs on isoprene and monoterpene emissions by tracking the seasonal and interannual changes in activity factors intrinsic to MEGAN’s empirically-based algorithms; this methodology maintained an environmentally consistent (i.e., “real-world”) set of model inputs. Within our eastern Texas study region, temperature was found to be the primary driver of seasonal and interannual variations of isoprene and monoterpene emissions estimates. Drought evolves through a complex interaction of land/atmosphere processes; typical components of drought include reductions in volumetric soil moisture and increases in land/atmospheric temperatures. Comparisons of results between drought and non-drought years reinforced the importance of temperature on predicted emissions; reductions in LAI and slight decreases in emissions associated with reduced soil moisture availability (isoprene only) during periods of drought were overwhelmed by emission increases caused by the much warmer temperatures.

Future Activities:

During the third year, we will (1) characterize and contrast the influence of a regionally-specific land cover dataset with high spatial resolution (30 m) to a widely used global land cover product derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) on biogenic emissions estimates in eastern Texas, (2) evaluate interannual variations in predicted dry deposition velocities and component surface resistances using two different dry deposition algorithms that are incorporated into the Comprehensive Air Quality Model with Extensions (CAMx), which has historically been used for air quality planning in the state, (3) simulate meteorological fields using the Weather Research and Forecast (WRF) model for representative average-to-wet and drought periods during 2006-2011 and compare predicted ozone and fine particulate matter distributions over eastern Texas climate regions using CAMx, and (4) explore spatial, seasonal, and annual variability in agricultural yields during 2006-2011 and implications for land cover characterization.

Journal Articles on this Report : 1 Displayed | Download in RIS Format

Other project views: All 11 publications 4 publications in selected types All 4 journal articles
Type Citation Project Document Sources
Journal Article Huang L, McDonald-Buller EC, McGaughey G, Kimura Y, Allen DT. Annual variability in leaf area index and isoprene and monoterpene emissions during drought years in Texas. Atmospheric Environment 2014;92:240-249. R835191 (2013)
R835191 (2014)
R835191 (Final)
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  • Abstract: ScienceDirect-Abstract
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  • Supplemental Keywords:

    biogenic emissions, drought, dry deposition, ozone, particulate matter, MEGAN, CAMx

    Progress and Final Reports:

    Original Abstract
    2012 Progress Report
    2014 Progress Report
    Final Report