Submitted by: John Hiatt, Conservation Chair
The Deserts of southeastern California and those lands on the east side of the Sierra Nevada Mountains, including most of Nevada, are the driest areas in the United States. Hence, the effects of changing climate are of particular interest. In order to understand what the future may have in store for our deserts it is necessary to understand some basic definitions and concepts.
Climate is often defined as weather averaged over time. While this is generally true, it misses the very important point that plant and animal communities are more heavily influenced by the extremes of weather than averages. The average annual daily high temperatures in Honolulu and Las Vegas only differ by a degree or two yet nobody who is familiar with these two places in January or July would mistake one for the other.
The term “global warming” is generally used to describe the changes causing melting of the arctic ice pack and glaciers worldwide, but for those of us at mid-latitudes and low elevation the term “global climate change” is more appropriate. If we think of climate change as an expression of a more energetic weather regime with greater extremes of rainfall, drought, and temperature we can begin to comprehend what the future may have in store for us. For plant communities the concept of “effective precipitation” as opposed to “total precipitation” is the key to understanding the relation between precipitation and plant life. Large areas of the Great Basin receive 8-10 inches of annual precipitation and so does the arctic slope in Alaska. The difference between the plant communities in these two places, the Great Basin Desert and Arctic muskeg lies in the evapotranspiration rates, or ET. The ET is the amount of water lost to the atmosphere be direct evaporation and transpired by the leaves of plants. In the Great Basin ET greatly exceeds precipitation while in the arctic rainfall exceeds ET. [Read more...]
