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Climate history and landscape change - RVDE

Activities > Climate History and Landscape Change

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Dust devil near Saratoga Springs, Death Valley. Photo by David Miller, USGS.

Climate, particularly precipitation, alters the desert landscape and the rate of recovery from natural and human disturbances. Yet, short-term (historical) natural climate variability and its influence on desert landscapes is not well known. The problem, therefore, is to understand climate variability and its effect on the physical components of the Mojave Desert ecosystem.

Methodology

Field studies on alluvial processes in the Mojave Desert provide evidence of the frequency and magnitude of hillslope runoff, debris-flow activity, and floodplain alluviation in desert washes.

Snow near the Granite Mountains in the Mojave National Preserve. Photo by Tonya Troxler, USGS.

These studies focus on identifying the timing of alluvial processes as well as developing a climate dataset based on daily observations of temperature and precipitation. Collected at 52 long-term weather stations, the data give a comprehensive picture of Mojave Desert climate for the period 1893-2000. Because archival data (original Weather Bureau records) were used, the temporal extent of these data is unusually long. This permits placement of recent data into a long-term context.

Highlights and Key Findings

Although the climate and landscape of the Mojave Desert, or any desert for that matter, are typically viewed as static and unchanging on historical time scales, this research demonstrates that climate, particularly precipitation, has varied substantially, and that the alluvial landscape is dynamic, changing in direct response to climate variation in many cases.

Precipitation in the Mojave Desert region varied substantially in the 20th century largely in response to global climate variability, specifically, El Niño/Southern Oscillation and the Pacific Decadal Oscillation. Multidecadal episodes of relatively moist conditions have alternated with dry conditions. The past two decades have been unusually wet with increased frequency of high- and low-intensity precipitation. The multidecadal episodes, particularly the drought-like conditions of 1942–1975 and the wet episode of 1976–1998, are contemporaneous with changes in the Pacific Decadal Oscillation. This relation suggests that the long-term climate of the Mojave Desert may be predictable. If so, the desert may undergo (or is now undergoing) drought-like conditions similar to those of 1942–1975.

One century of Mojave Desert precipitation data, summarized as the long-term average (horizontal line), dry years (below the line), and wet years (above the line). Purple indicates drier years and green indicates wetter years.These long periods correspond to the Pacific Decadal Oscillations that influence weather throughout the western U.S.

The implications for land management are that policies established from research done in the past two decades may not apply in another, drier climate scenario. Moreover, climate variation in a majority of the cases altered the frequency of surface runoff and sediment yield, the occurrence of debris flows, and alluviation in the major washes. The net effect has been temporal clustering of geomorphic activity that coincides with the main episodes of wet and dry climate as discussed above.

Products

Hereford, R., Webb, R.H., and Longpre, C.I., 2004, Precipitation history of the Mojave Desert region, 1893-2001: U.S. Geological Survey Fact Sheet 117-03, 4 p.

Hereford, R., and Longpre, C., 1998, Climate history of the Mojave Desert region, 1892 -1996, including data from 48 long-term weather stations and an overview of regional climate variation, USGS website.

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