Climatological Conditions Driving Lake Levels During Past Cold and Warm Periods in Western North America

Abstract:

Terrestrial paleoclimate records from target time periods provide information to benchmark the amount and distribution of precipitation simulated by climate models. Evidence for the persistence of large inland lakes in western North America during the Pliocene and Pleistocene provides first-order constraints on regional water balance. The spatial distribution of terminal lakes records the interaction between regional moisture delivery dynamics and topography. We investigate the climatological conditions driving lake levels in western North America during the mid-Pliocene warm period and Pleistocene glacial maxima. Geologic evidence suggests wet conditions persisted in this region during both periods despite dramatically different boundary conditions and pCO₂ levels.

We modify the pluvial hydrologic index, a dimensionless measure of lake surface area to the draining tributary area, to include watershed rainfall-runoff relationships and basin-scale vapor recycling. We do so by including water isotope constraints and calibrated Budyko curves at the individual watershed scale. We apply this modeling framework to the spatial distribution of terminal lakes documented in the Basin and Range during Pleistocene glacials and during the Pliocene. The results are quantitatively compared to climate model simulations of the Last Glacial Maximum (LGM, ~21 ka) and mid-Pliocene (~3 to 3.3 Ma) from the Paleoclimate Modelling Intercomparison Project (PMIP and PlioMIP). Reduced evaporation and moderate increases in precipitation, relative to modern, drive lake levels during the LGM, while large precipitation increases are the primary driver during the Pliocene. Water isotope constraints in our lake mass balance model bring precipitation estimates in closer agreement with those from climate model simulations. Future inclusion of lakes in climate model boundary conditions will improve both the simulation of inland vapor recycling and proxy-model agreement in western North America.