|Holifield Collins, Chandra|
|Scott, Russell - Russ|
Submitted to: Water Resources Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/18/2008
Publication Date: 5/20/2008
Citation: Holifield Collins, C.D., Emmerich, W.E., Moran, M.S., Hernandez, M., Scott, R.L., Bryant, R., King, D., Verdugo, C.L. 2008. A remote sensing approach for estimating distributed daily net carbon dioxide flux in semiarid grasslands. Water Resources Research, Vol. 44, W05S17, doi:10.1029/2006WR005699. Interpretive Summary: Semiarid grasslands cover a significant portion of the Earth’s land surface and may play an important role in absorbing atmospheric carbon dioxide (CO2). Atmospheric CO2 is increasing and the potential impact on climate change has caused an increased effort to more accurately determine how much CO2 is being released and absorbed by land surfaces. Local scale measurements of CO2 flux (release and absorption) are being made using micrometeorological instrumentation at various locations around the world, but measurements at a larger scale are needed. Information that can be obtained from satellite imagery has the potential to provide measurements at this larger scale. In this study, Landsat satellite imagery was combined with local measurements of CO2 flux to create maps of daily net CO2 flux estimates over an area of semiarid grassland spanning 2,224 acres in southeastern Arizona. These regional maps have great potential as a tool for better understanding the role of semiarid grasslands in the carbon cycle.
Technical Abstract: Semiarid systems compose a significant portion of the world’s terrestrial area and may play an important role in the global carbon cycle. A model was developed using the relation between surface reflectance and temperature obtained from satellite imagery to determine a Water Deficit Index (WDI) that estimated distributed plant transpiration, and by extension carbon dioxide (CO2) flux, for a point in time. Relationships were developed to scale these instantaneous flux measurements up to daytime estimates, which were then used to obtain measures of nighttime flux. Satellite images were acquired for a five-year period (1996-2000) during which transpiration and net CO2 flux were measured for a semiarid grassland site in southeastern Arizona. Manual and automatic chamber data were also collected at the same site during the monsoon growing seasons of 2005 and 2006 and used to develop the relationship between and daytime and nighttime CO2 flux. Strong linear relationships were found between WDI-derived instantaneous and daytime net CO2 flux estimates (R2 = 0.97), and between daytime and nighttime fluxes (R2=0.88). These relations were used to generate maps of distributed total daily net CO2 flux. The error for the model was within the range of error inherent in the data sets used to create it, and remained reasonable when used with WDI values less than 0.9. This study demonstrated that remote sensing can offer a physically-based means of obtaining daily net CO2 flux in semiarid grasslands.