Showing papers by "Gordon B. Bonan published in 1999"
TL;DR: In this article, a 10-yr climate simulation with a global climate model using natural and modern vegetation maps for land surface boundary conditions showed that the conversion of forest to cropland in the eastern and central United States cooled climate.
Abstract: The modern vegetated landscape of the United States little resembles the “natural” landscape prior to colonial settlement. Two 10-yr climate simulations with a global climate model using natural and modern vegetation maps for land surface boundary conditions showed that the conversion of forest to cropland in the eastern and central United States cooled climate. Mean annual surface air temperature decreased by 0.6°–1.0°C in the United States east of 100° W. The decrease in daily maximum temperature exceeded that for daily minimum temperature for a decreased diurnal temperature range of about 0.6°C, averaged over the year. The cooling was greatest in the Midwest in summer and autumn, when daily mean temperature decreased by >0.5° and 2.5°C, respectively; daily maximum temperature decreased by 1°–3°C; and diurnal temperature range decreased by about 1°C. U.S. temperature records show that much of the 1800s was anomalously cold, particularly in summer and autumn in the Midwest. Although this was likely cause...
149 citations
TL;DR: In this paper, the sensitivity of regional terrestrial climate to the characteristics of tundra ecosystems has been investigated by a series of sensitivity experiments concentrating on the summer of 1995, and the results indicate that vegetation variation within the Arctic has substantial climatic effects that extend beyond the Arctic.
Abstract: The sensitivity of regional terrestrial climate to the characteristics of tundra ecosystems has been investigated by a series of sensitivity experiments concentrating on the summer of 1995. Validation of the NCAR Land Surface Model and the Arctic Regional Climate System Model for this season indicate their adequacy for this study. Comparisons of the simulated climate in response to a wet meadow tundra or a dry heath tundra results in an expected cooling and moistening of both the local area and the adjoining sea ice and forested regions. The impact of atmospheric cloud-radiation feedbacks is to reduce the cooling as the summer progresses, although moistening continues, associated with increased precipitation in some areas. The spatial variability of the response is dependent upon prevailing synoptic conditions, which act to enhance moisture advection in certain areas. This study indicates that vegetation variation within the Arctic has substantial climatic effects that extend beyond the Arctic. In addition, the perturbations in the summer season could have profound implications of Arctic wintertime climate and issues of snow-albedo feedback and spring melt.
66 citations