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biotaModern Climatic Conditions on the Colorado Plateau

Capitol Reef

Monsoon clouds over a classic "strike valley" along the eastern edge of Capitol Reef National Park. Photo © 1999 Ray Wheeler

Much of the Colorado Plateau is considered arid or semi-arid with annual precipitation amounts in most areas of less than 10 inches. The high plateaus and small mountain ranges, however, receive considerably more precipitation than the more widespread middle and lower elevations due to orographic lifting and cooler temperatures. Most areas above 8000 feet receive 20-25 inches annually, while mountains above 11,000 feet often receive about 35 inches per year.

Climatic patterns vary from south to north across the Colorado Plateau. Much of the northern Plateau shares a climatic regime with the Great Basin. The region generally lies outside the typical major pathways of winter and summer moisture-bearing masses. Winter moisture comes infrequently from Pacific air masses, and summer are generally hot, with infrequent convective rainfall.

streamflow.gif (4555 bytes)

Streamflow data from Holbrook, Arizona shows the bi-seasonal precipitation regime typical of the southern Colorado Plateau.

The southern Colorado Plateau, however, has a bi-seasonal precipitation regime, with distinct precipitation maxima in both the winter mer seasons. Winter precipitation comes from incursions of Pacific air, while summer precipitation is monsoonal, with a moisture source to the south, southwest, or southeast. Precipitation is low to moderate in the early winter, increasing in February and March, and then dropping off quickly into April. May through June are very dry throughout the region. Precipitation increases in July with the advent of the Arizona summer monsoon, particularly on the southern Plateau. During this time a large dome of high pressure sitting over eastern New Mexico and Texas drives warm, moist air from the Gulf of Mexico into the Southwest. Rapid daytime heating leads to upwelling of the moist air and the formation of widespread and occasionally intense thunderstorms.

The monsoon can continue into mid-September but more commonly ends in late August or early September. With the onset of autumn comes dry conditions and sunny skies. Temperatures begin to cool and often an extended period of comfortable, fair weather ensues. Conditions commonly remain dry until the first winter cyclonic storms develop and pass through the region beginning roughly in late September or November in the north and as late as December on the southern Plateau.

These bi-seasonal and north-south climatic gradients have led to development of a vegetation gradient as well, with species more dependent upon summer precipitation occurring dominantly in the southern and southeastern Colorado Plateau and declining toward the northwest. Locally, these generalizations are modified by high topographic diversity.

Click here for a discussion of the importance of climate studies to understanding the land cover history of the Colorado Plateau.
Click here for a description of the causes of long-term cycles of climate change in the Southwest (off-site).


Research:

Fire-Southern Oscillation Relations in the Southwestern United States. A close linkage between fire and climate could diminish the importance of local processes in the long-term dynamics of fire-prone ecosystems. The structure and diversity of communities regulated by fire may have nonequilibrial properties associated with variations in global climate. Successful prediction of vegetation change hinges on a better understanding of climatically driven disturbance regimes and the relative contributions of regional versus local processes to community dynamics. Adapted from a journal article by Thomas W. Swetnam and Julio L. Betancourt.


Resources:

Gutzler, D. S. and Preston, J. W. 1997. Evidence for a relationship between spring snow cover in North America and summer rainfall in New Mexico. Geophys. Res. Lett. 24: 2207-2210.

Hereford, R. and Webb, R. H. 1992. Historic variation of warm-season rainfall, southern Colorado Plateau, southwestern U.S.A. Climate Change 22: 239-256.

Higgins, R. W., Yao, Y. and Wang, X. L. 1997. Influence of the North American monsoon system on the United States summer precipitation regime. J. Climatology 10: 2600-2622.

Lin, G., Phillips, S. L. and Ehleringer, J. R. 1996. Monsoonal precipitation responses of shrubs in a cold desert community on the Colorado Plateau. Oecologia 106: 8-17.

Mitchell, V. 1976. The regionalization of climate in the western United States. Journal of Applied Meteorology 15: 920-927.

Mock, C. J. 1996. Climatic controls and spatial variations of precipitation in the western United States. Journal of Climate 9: 1111-1125.

Neilson, R. P. 1986. High-resolution climatic analysis and southwestern biogeography. Science 232: 27-34.

Neilson, R. P. 1993. Ecotone response to climate change. Ecological Applications 3: 385-395.

NOAA. National Climatic Data Center. <http://www.ncdc.noaa.gov/> 8/1.

Pearson, G. A. 1931. Forest types in the southwest as determined by climate and soil. Technical Bulletin 247. USDA Forest Service, Washington, D.C., 27 pp.

Peterson, K. L. 1994. Modern and Pleistocene climatic patterns in the west. In:  Harper, K., Clair, L. L. S., Thorne, k. H. and Hess, W. M., editors. Natural history of the Colorado Plateau and Great Basin. University Press of Colorado, Niwot.

Richmond, A. J., Jr. 1987. Historic precipitation sequences on the Colorado Plateau, 1859-1983. M.S. Thesis. Northern Arizona University, Flagstaff, AZ.

Ropelewski, C. F. and Halpert, M. S. 1986. North American precipitation and temperature patterns associated with the El Niño/Southern Oscillation (ENSO). Monthly Weather Review 114: 2352-2362.

Savage, M., Brown, P. M. and Feddema, J. 1996. The role of climate in a pine forest regeneration pulse in the southwestern United States. Ecoscience 3: 310-318.

Sellers, W. D. and Hill., R. H., editors. 1974. Arizona climate, 1931-1972. University of Arizona Press, Tucson, AZ.

Slack, J. R. and Landwehr, J. M. 1992. Hydro-Climatic Data Network (HCDN)---A U.S. Geological Survey streamflow data set for the United States for the study of climate fluctuations, 1874-1988.Open-File Report 92--129. U.S. Geological Survey, Washington, D.C., 193 pp.

Swetnam, T. W. and Betancourt, J. L. 1990. Fire-Southern Oscillation relations in the southwestern United States. Science 249: 1017-1021.

Swetnam, T. W. 1990. Fire history and climate in the Southwestern United States. Pp. 6-17 In:  Krammes, S. J., editor. Proceedings of Symposium on Effects on Fire in Management of Southwestern Natural Resources. General Technical Report RM-191.   U.S. Forest Service.

Swetnam, T. W. and Betancourt, J. L. 1992. Temporal patterns of El Niño/Southern Oscillation - wildfire teleconnections in the southwestern United States. Pp. 259-270 In:  Diaz, H. F. and Markgraf, V., editors. Historical and paleoclimatic aspects of the Southern Oscillation. Cambridge University Press, New York, NY.

Swetnam, T. W. and Betancourt, J. L. 1998. Mesoscale disturbance and ecological response to decadal climatic variability in the American Southwest. Journal of Climate 11: 3128-3147.

style="mso-pagination:none;mso-layout-grid-align:none; Tarboton, D. G. 1994. The source hydrology of severe sustained drought in the Southwestern United States. Journal of Hydrology 161: 31-69.

Touchan, R., Allen, C. D. and Swetnam, T. W. 1996. Fire history and climatic pattens in ponderosa pine and mixed-conifer forests of the Jemez Mountains, northern New Mexico. Pp. 179-195 In:  Allen, C. D., editor. Fire Effects in Southwestern forests: Proceedings of the Second La Mesa Fire Symposium. General Technical Report RM-286.   USDA Forest Service, Fort Collins, CO.

Van Devender, T. R. and Spaulding, W. G. 1979. Development of climate and vegetation in the southwestern United States. Science 204: 701-710.