A User's Guide to the VEMAP Phase 1 Database

The Vegetation/Ecosystem Modeling and Analysis Project (VEMAP) is an ongoing multi-institutional, international effort addressing the response of biogeography and biogeochemistry to environmental variability in climate and other drivers in both space and time domains. The objectives of VEMAP are the intercomparison of biogeochemistry models and vegetation-type distribution models (biogeography models) and determination of their sensitivity to changing climate, elevated atmospheric carbon dioxide concentrations, and other sources of altered forcing. The VEMAP exercise allows us to identify important commonalties and differences among model controls and responses. Where the models differ, the comparison highlights areas of uncertainty or error and identifies problems for future research. Inter-model differences also help to quantify the uncertainty in modeled responses to changing climate and other drivers. The completed Phase I of the project was structured as a sensitivity analysis, with factorial combinations of climate (current and projected under doubled CO2), atmospheric CO2, and mapped and model-generated vegetation distributions. The highly structured nature of the intercomparison allowed rigorous analysis of results, while constraining the range of questions explored. Maps of climate, climate change scenarios, soil properties, and potential natural vegetation were prepared as common boundary conditions and driving variables for the models (Kittel et al. 1995). As a consequence, differences in model results arose only from differences among model algorithms and their implementation rather than from differences in inputs. Results from VEMAP I are reported in VEMAP Members (1995) and selected files are available through UCAR's anonymous FTP server (see Section 2.3). Abstracts describing the six modeling groups participating in VEMAP Phase I can be found under the subdirectory /docs. The VEMAP input database for the Phase I model intercomparison is documented in this Technical Note. It includes compiled and model-generated datasets of long-term mean climate, soils, vegetation, and climate change scenarios for the conterminous United States. The data are on a 0.5? latitude/longitude grid. There are both daily and monthly representations of the mean climate. The climate data and climate change scenarios are presented in both gridded and time-sequential format. We developed the time-sequential, "site" file format to facilitate extractions of information for individual grid cells (Sections 4.3 and 12).