THE GROUNDWATER-CLIMATE CONNECTION: AMPLIFICATION OF SEASONAL TO CENTURY SCALE OSCILLATIONS IN CLOSED BASINS

In the western US, the Great Basin region of the Basin and Range physiographic province, and individual closed-lake basins (e.g. the Great Salt Lake), form a macrocosm of the water cycle where a balance of regional-scale natural and human impacts can be studied in a system forced by global weather and climate. Topographically and hydrologically, the region is a closed system, in that no rivers drain the region, and the water cycle is completed through a balance of precipitation and evaporation. It is often held that closed basins have the effect of “amplifying” the climate or the orbital signal. However, the physical mechanism to explain the dominant low-frequency behavior of lake fluctuations is largely based on the relatively short time scales of surface processes. Evidence suggests that low-frequency components in the Great Salt Lake level/volume record (Lall and Mann, 1995; Mann et al. 1995), are consistent with the El Nino-Southern Oscillation, quasi-biennial, quasi-decadal signal. The sun-climate relation has also been proposed to be correlated with lake levels (e.g. Hoyt and Schatten, 1997). However, the physical role that the basin-lake hydrology, topography and geology play is unresolved.

A preliminary hypothesis is that random fluctuations and weak low-frequency oscillations in seasonal to interdecadal climatic/solar forcing in closed basins, may interact with the longer time scales of deeper soil-moisture and groundwater storage to amplify low-frequency modes in runoff and lake levels. A discussion of how weather and thermal noise might amplify groundwater-lake levels through a phenomenon known as stochastic resonance. The role of nonlinear processes, feedbacks and threshold effects are described in terms of mountain-front runoff (e.g. groundwater-stream-lake interaction) as well as lake-groundwater evaporation.