UC Riverside

Soil temperature plays an important role in physical, biological and microbiological processes occurring in the soil. It can be used as indicative of regional climate change. A long-term soil temperature database was collected at 75 locations in the Mojave Desert region by the Pallmann method from 1982-2000. This long-term database of soil temperature is invaluable and was used to analyze the spatiotemporal change pattern of soil temperature, and to examine the relationship between regional climate change and soil temperature over an extended period of time.

The main conclusions of this research are: 1) the accuracy and consistency of the Pallmann method was good in comparison with two other temperature measurement methods: thermistor sensor and diffusion-cell method. The Pallmann method is an ideal method for studying the spatial variation in soil temperature and long-term climate changes. 2) Elevation is the dominated factor governing the spatial variation of soil temperature in the Mojave Desert region and can be used to estimate the spatial distribution of soil temperature. In the Mojave Desert region, hyperthermic soil is the most extensive one, which accounts for around 55% of the whole region. Thermic soil accounts for 38.7%. Frigid and mesic soils only occur at high elevation mountains. 3) Seasonal soil temperatures vary greatly in the Mojave Desert region and decrease linearly with elevation. The differences of the summer and winter soil temperature are around 20 °C under the same elevation. The effect of elevation on soil temperature is more pronounced in summer season than in winter season. 4) Soil and air temperature are highly correlated in the Mojave Desert region. Both of the soil and air temperature were found to be highly correlated with elevation and their spatiotemporal variations are highly positively correlated. 5) The Mojave Desert is experiencing a warming trend. Based on continued measurements across the region, the air and soil temperatures have risen at the rates of 0.79 and 0.63°C per 10 year from 1982 to 2000. The anomalies of annual precipitation were inversely correlated with those of soil temperature. The soil temperature of the Mojave Desert would be cooler than normal under El Niño conditions. 6) The climatic variables of air temperature, precipitation and evaporation had significant correlation with soil temperature. The spatial-temporal variation of soil temperature can be predicted based on the linear regression equation with air temperature and precipitation as independent variables.