Ecological Controls on Water Cycle Response to Climate Variability Study Funded by U.S. Department of Energy Pantex Plant

Bridget R. Scanlon, principal investigator

Understanding relationships between climate forcing, ecology, and hydrology is critical for waste containment in semiarid/arid regions. This study focused on evaluating the role of vegetation in controlling the impact of climate forcing on subsurface water movement by analyzing detailed weighing lysimeter data from the Nevada Test Site within the Mojave Desert, Nevada . Results of the study indicate that the impact of climate variability on the water cycle in desert ecosystems is controlled by biospheric feedbacks at interannual to millennial timescales. The study describes a unique field data set from weighing lysimeters beneath nonvegetated and vegetated systems that unequivocally demonstrates the role of vegetation dynamics in controlling water-cycle response to interannual climate variability related to El Niño Southern Oscillation (ENSO) in the Mojave Desert, USA. Extreme El Niño winter precipitation (2.3 to 2.5 times normal) typical of the U.S. Southwest would be expected to increase groundwater recharge, which is critical for water resources in semiarid and arid regions. However, lysimeter data indicate that rapid increases in vegetation productivity in response to elevated winter precipitation reduced soil water storage to half of that in a nonvegetated lysimeter, thereby precluding deep drainage below the root zone that would otherwise result in groundwater recharge. Vegetation dynamics have been controlling the water cycle in interdrainage desert areas throughout the U.S. Southwest, maintaining dry soil conditions and upward soil water flow since the last glacial period (10,000 to 15,000 yr ago), as shown by soil water chloride accumulations. Although measurements are specific to the U.S. Southwest, correlations between satellite-based vegetation productivity nd elevated precipitation related to ENSO indicate that this model may be applicable to desert basins globally. Understanding the two-way coupling between vegetation dynamics and the water cycle is critical to predicting how climate variability influences hydrology and water resources in water-limited landscapes.

 

For more information, please contact:

Bridget R. Scanlon, principal investigator. Telephone (512) 471-8241;
E-mail bridget.scanlon@beg.utexas.edu.

July 2005