Abstract

Some internally draining lakes in northwestern New South Wales, Australia, are contained in structural basins but owe their lack of external outlets to arid climate. Former high lake shorelines are defined in part by precipitated crusts or by deltas. Radiocarbon dating, although as yet less than satisfactory, suggests that the high lake stands occurred not later than about 14,500 B.P. They may eventually be correlated with lacustrine episodes that, elsewhere in inland New South Wales, occurred in the range 23,500 to 15,500 B.P. Whether or not the lakes under discussion existed at the time of maximum cold is uncertain; but they were indubitably associated with low paleotemperatures.

Reconstruction of former temperatures involves little or no controversy. Use of paleotemperatures to reconstruct former evaporation rates produces results that stand up well to checking. Manipulation of the equilibrium equations for closed lakes produces precipitation equations that involve evaporation, area ratio between lake and rest of basin, and evapotranspiration. Empirical studies and some paleohydrologic work supply values or ranges of evapotranspiration and basin loss. Even in the lowest observed or estimated range of evapotranspiration, the precipitation equations indicate former precipitation about 50 percent greater than that of today. Calculation of evapotranspiration rates for former conditions of radiation and temperature and for a range of sunshine incidence, and entry of these rates into the precipitation equations, show that very low values of sunshine incidence would be required to drive calculated precipitation down to, or below, today's levels. That is to say, any hypothesis that the former high lake stands were associated with reduced precipitation demands inordinately low rates of evapotranspiration, plus a combination of reduced precipitation with inordinately high cloudiness.

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