Historical Climate Series (TCLIMATE)
The first objective for VEMAP Phase 2 dataset development is the creation of a ~100-year gridded monthly and daily time series of climate for the conterminous United States that includes realistic interannual variability.
A beta-version of the VEMAP2 1895-1993 multivariate climate dataset was completed in early 1998 and distributed to VEMAP participants for evaluation and preliminary model runs. A final version of the historical dataset has since then been publicly released . This effort was in collaboration with the NSF Geophysical Statistics Project at NCAR. Development of the dataset is reported in Kittel et al. (1997).
As in the VEMAP1 database,
the historical dataset has: (1) daily and monthly versions, (2) physical
consistency among variables on a daily basis, (3) consistency between climate
and topography, and (4) needed input variables for VEMAP2 models (minimum
and maximum temperature, precipitation, vapor pressure, and solar radiation).
Key steps in the development of the gridded, multivariate, monthly and daily historical dataset were:
(1) Input monthly datasets. Monthly mean minimum and maximum temperature (Tmo) and monthly precipitation (PPTmo) historical time series were derived from:
(a) NCDC's Historical Climate Network (HCN) monthly data from 1895 (~1200 stations)
(b) Shorter period (e.g., 1951-1990) cooperative network monthly station data (for an additional ~6000-8000 stations)
(c) SNOTEL site data
This merged input dataset provides a high density of stations
and adequate-to-excellent spatial sampling of climate throughout most of
the conterminous U.S., including at higher elevations (primarily from the
(2) Serially-complete records. We created serially-complete 99-year monthly min/max Tmo and PPTmo records for climate stations from Step(1) using a local (moving-window) kriging model, following Haas (1990, 1995) (Royle et al., in preparation, Kittel et al. 1997). The model imputes monthly climate anomalies where station records are discontinuous or limited in length.
(3) Spatial interpolation with topographic adjustment.
The serially complete station data were then passed to Chris Daly
(Oregon State University) for spatial interpolation with topographic adjustment.
Min/max temperature and precipitation station data were spatially interpolated
to the 0.5deg. lat/long VEMAP grid for each month in the 99-yr record using
a newly expanded version of PRISM (Daly et al., submitted). PRISM incorporates
elevation, aspect, and other topographic information to grid temperature
and precipitation data. Daly was funded for this task by USDA Forest Service
Global Change Research Program.
(4) Daily temperature and precipitation generation. We generated daily min/max temperature and precipitation using a modified version of Richardson's (1981, Richardson and Wright 1984) stochastic weather generator WGEN. The version was provided by Sue Ferguson (USFS) and incorporated modifications from Rick Katz and Linda Mearns (NCAR). We further modified the code to permit separate parameterizations for wet vs. dry periods in the record (following the work of Dan Wilks).
We parameterized the model based on HCN and coop network daily station data and ran it for the VEMAP grid for the 99-yr record. The daily values were constrained by gridded monthly T and PPT data from step (3), so that the daily and monthly versions of the historical dataset represent the same climate.
As part of our quality checking process, we compared daily
statistics from the gridded, generated product and station data. We found
that daily frequency distributions and extremes match well for a range of
climates across the domain.
(5) Estimation of solar radiation and humidity. We implemented a new version of MTCLIM (version 3; Thornton et al., in preparation) for VEMAP2 to create daily (and monthly) vapor pressure (VP), daytime relative humidity, total incident solar radiation (SR), and irradiance (IRR) from daily T and PPT. This version of MTCLIM includes improved estimation of radiation and humidity, as developed by Peter Thornton, Steve Running, John Kimball, and Rob Kremer (U. of Montana) (Kimball et al. 1997, Thornton et al., in preparation).
Generated vapor pressure fields compare well with the Marks (1990) VP climatology and simulated SR with NCDC/NREL SAMSON data. In the coming year, we plan to extend coverage for the historical dataset to Alaska and Hawaii. The domain of the Alaskan dataset will include northwestern Canada (Yukon, etc.).
For VEMAP2, our second major objective is to develop transient climate change scenarios based on coupled atmosphere-ocean general circulation model (AOGCM) transient climate experiments. The purpose of these scenarios is to reflect time-dependent changes in surface climate from AOGCMs in terms of both (1) long-term trends and (2) changes in multiyear (3-5 yr) to decadal variability patterns, such as ENSO.
We have processed scenarios from transient greenhouse gas
experiments with sulfate aerosols from the Canadian
Climate Center (CCC) and the Hadley Centre (HADCM2; Mitchell et al.
1995, Johns et al. 1997); accessed via the Climate
Impacts LINK Project, Climatic Research Unit, University of East Anglia.
We also plan to process model output from GFDL and the NCAR
CSM when these become available.
Haas, T.C. 1990. Lognormal and moving window methods of estimating acid deposition. J. Amer. Stat. Assoc. 85:643-652.
Haas, T.C. 1995. Local prediction of a spatio-temporal process with an application to wet sulfate deposition. J. Amer. Stat. Assoc. 90:1189-1199.
Johns T.C., Carnell R.E., Crossley J.F., Gregory J.M., Mitchell J.F.B., Senior C.A., Tett S.F.B. and Wood R.A. 1997 The Second Hadley Centre coupled ocean-atmosphere GCM: Model description, spinup and validation. Climate Dynamics 13:103-134.
Kimball, J S, Running, S W, and Nemani, R. 1997. An improved method for estimating surface humidity from daily minimum temperature. Agricultural and Forest Meteorology. 85:87- .
Kittel, T.G.F., J.A. Royle, C. Daly, N.A. Rosenbloom, W.P. Gibson, H.H. Fisher, D.S. Schimel, L.M. Berliner, and VEMAP2 Participants. 1997. A gridded historical (1895-1993) bioclimate dataset for the conterminous United States. Pages 219-222, in: Proceedings of the 10th Conference on Applied Climatology, 20-24 October 1997, Reno, NV. American Meteorological Society, Boston.
Marks, D. 1990. The sensitivity of potential evapotranspiration to climate change over the continental United States. Pages IV-1 - IV-31 in: Biospheric feedbacks to climate change: The sensitivity of regional trace gas emissions, evapotranspiration, and energy balance to vegetation redistribution. Gucinski, H., Marks, D., and Turner, D.P. (eds.) EPA/600/3-90/078. U.S. Environmental Protection Agency, Corvallis, OR.
Mitchell J.F.B., Johns T.C., Gregory J.M. and Tett S. 1995 Climate response to increasing levels of greenhouse gases and sulphate aerosols. Nature 376:501-504.
Neilson, R.P., I.C. Prentice, B. Smith, T. Kittel, and D.Viner. 1997. Simulated changes in vegetation distribution under global warming. Annex C, pp. 439-456, in: Watson, R.T., M.C. Zinyowera, and R.H. Moss (eds.), The Regional Impacts of Climate Change. An Assessment of Vulnerability. A Special Report of the IPCC Working Group II. Cambridge University Press, New York.
Richardson, C.W. 1981. Stochastic simulation of daily precipitation, temperature and solar radiation. Water Resources Research 17:182-190.
Richardson, C.W., and D.A. Wright. 1984. WGEN: A Model for Generating Daily Weather Variables. U.S. Department of Agriculture, Agricultural Research Service, ARS-8, p 83.
Royle, J.A., L.M. Berliner, N. Rosenbloom, T. Kittel, and D. Schimel. Construction and evaluation of the VEMAP long-term precipitation data set. In preparation.
Royle, J.A., L.M. Berliner, N. Rosenbloom, T. Kittel, and D. Schimel. Construction and evaluation of the VEMAP long-term temperature data set. In preparation.
Thornton, P., et al. Daily surface radiation and humidity
algorithms for the MT-CLIM model: implementation and testing over the continental
U.S. In preparation.
Page authors: T. Kittel, D.S. Schimel, N. Rosenbloom, H. Fisher, A. Royle, C. Daly, P. Thornton and C. Kaufman.