27th Annual Meeting and Symposium of the
Desert Tortoise Council, March 22-24, 2002
Abstracts

The Tortoise and the Hare: The Varied Paces of Desert Climates

Kelly T. Redmond
Regional Climatologist, Western Regional Climate Center, Desert Research Institute, Reno, Nevada

This talk will cover the main general aspects of the climates of the Southwest where desert tortoises are found.

1) Time-averaged or "static" characteristics. These include things such as the spatial distribution of annual precipitation, the seasonal cycle of precipitation and its variations in space (including altitude), and the principal "precipitation seasons" (primarily winter, and the summer monsoon). Paradoxically, in this driest of all climates, water is a major element of change. The way in which water arrives and causes things to happen plays a strong role in the resulting biology that we observe. Essentially, not much happens (or appears to) for very great lengths of time, interspersed with short periods where a lot happens. Much of life revolves around preparing for and responding to these short episodes, at least as regards moisture. For temperature, a different set of issues are at work, including long periods of life-threatening extremes, large day-night differences, and occasional frosts or cold extremes. Humidity is generally very low, but gets very high when the monsoon invades. The progression of the monsoon will be presented.

2) Temporal variations. Climate is constantly varying on all time scales. There is no true "normal" climate, except in an approximate sense. The factors which produce the "static" climate mentioned above are generally different for different seasons, and there is no particular reason why the variations through time for one season should be the same as for other seasons. Mean conditions can vary from year to year, decade to decade, century to century, and so on. Similarly, the likelihood of "events" can vary over the same time scales. Examples of "events" are heavy downpours, extended wet spells, playa flooding, tropical storms, and so forth. The relation between event occurrence and average climate conditions is not always clear. The variations in climate can express themselves as slow changes, or as regimes separated by fast transitions. Usually these variations reflect influences from other more distant parts of the climate system.

3) Spatial connections. Local climates cannot be properly understood from purely local perspectives. The climate at a spot (any spot on earth) is the local expression of an integrated system involving connections across a range of scales from a few meters to the size of the earth. All these scales matter. Among the climate connections we know about for this area, the behavior of the faraway tropical Pacific Ocean is known to have influences on the winter precipitation of this area, both positive and negative.

4) Monitoring and data. How do we know what we know about desert climates? There are particular and peculiar difficulties in making long term measurements, including access and inhospitability issues, the extreme spottiness of precipitation, degree of sampling in space (mountains versus valleys, especially), accurately capturing rare but significant events, various presumptions about what we expect to find via measurement, and methods of distilling and disseminating findings gleaned from these observations.

5) Change. As time permits, some thoughts on change and stasis in desert climates, and on climate in general, will be offered.

Web Pages 

http://www.wrcc.dri.edu 
Background climates for particular stations

http://www.wrcc.dri.edu/climsum.html 
Precipitation maps

http://www.wrcc.dri.edu/precip.html (esp regional, and pct annual) 
Excessive precipitation rates, return values for engineering

http://www.wrcc.dri.edu/pcpnfreq.html
ENSO connections 

http://www.wrcc.dri.edu/enso/soipcpn.html 

http://www.wrcc.dri.edu/enso/maps.html
Hourly historical data from around the Nevada Test Site, low to high desert

http://www.cemp.dri.edu/index.html 
Recent climate behavior from airports

http://www.wrcc.dri.edu/recent_climate.html 
Divisional climate data, highly interactive, 1895 thru latest month

http://www.wrcc.dri.edu/divisional.html 
A potpourri of climate monitoring information, relevant to the West

http://www.wrcc.dri.edu/monitor/wdccmon.html 
Abstracts from a recent workshop relevant to this area, including climate 

http://www.wmrs.edu/SW-GreatBasin/abstracts.htm