A comparison of summertime water and CO2 fluxes over rangeland for well watered and drought conditions

Continuous measurements of the surface energy balance components (net radiation Rn, sensible heat flux H, latent heat flux LE, ground heat flux G, and CO2 fluxes began in early June of 1995 at the Little Washita Watershed, near Chickasha, Oklahoma. A severe drought during 1998 provided a unique opportunity to evaluate the range of fluxes that can be expected during the summer period. Data obtained during four continuous summer periods were used to evaluate the year-to-year variability in summertime energy and CO2 fluxes. During the summer period (day 150–240), total evapotranspiration for non-drought years ranged from 224 to 273 mm with a mean and standard error of 253 ± 12 mm. The mean and standard error of the net ecosystem exchange (NEE) rate of carbon dioxide for the same summer period was −120 ± 36 g C/m2. In a year with severe drought (1998) total evapotranspiration for the summertime period was 145 mm. The lack of precipitation during this time resulted in total losses to the atmosphere of 155 g C/m2 from soil respiration. © 2001 Elsevier Science B.V. All rights reserved.