THE TIMING AND MAGNITUDE OF LAKE-LEVEL VARIABILITY, IN RESPONSE TO INTERANNUAL CLIMATE VARIABILITY

Some of the primary uncertainties and most critical consequences of both past and future climate change concern Earth's hydrological cycle. Lakes are key indicators of a region’s hydrological cycle, directly reflecting the basin-wide balance between evaporation and precipitation. Lake-level records can therefore hold valuable information about the history of these climate variables. However, the interpretation of such records is not necessarily straightforward; because lakes integrate year-to-year climate fluctuations they will exhibit persistent fluctuations on timescales of decades or more. Any system with 'memory' (i.e., inertia, or a dynamic response time) will produce similar behavior. This inertia can make it difficult to distinguish lake-level fluctuations in response to stochastic climate forcing from a true shift in the climate -- a change in the mean or standard deviation of one or several climatic variables. The size and shape of a lake determines the response time to both stochastic forcing and climatic change, meaning that each individual lake will respond with a unique timescale and magnitude.

We develop a general lake-level model to constrain a lake’s response to interannual climate fluctuations. Because of its long historical lake-level and climatological records, we use the Great Salt Lake as a case-study for this work. We use mass-balance models to track the lake’s response to synthetic, random time series of precipitation and evaporation, then compare the magnitude and frequency of our model’s response to the historical record of the Great Salt Lake’s rise and fall. We then compare simplified geometric representations of several lakes to illustrate how the timing and amplitude of a lake’s response differs under unique climatic and geometric scenarios. We find that interannual climate variability alone can explain much of the decadal-centennial variations in the lake-level record. It is only after removing this background variability that a lake's response to a true climatic shift can be understood.