THE RESPONSE OF LAKE LEVELS AND AREAS TO CLIMATE-CHANGE

The levels and areas of lakes, particularly closed lakes (those withou t outlet) are known to be sensitive indicators of changes in climate, and so in principle they can play a role in monitoring current and fut ure climatic changes. In this paper we derive solutions to the water b alance equation giving the response of the level and area of closed la kes to steps, spikes and sinusoidal variations in aridity, and show th at such a lake acts approximately as a simple low pass filter having a characteristic equilibrium response time tau(e). We also review the s imilar response of open lakes to changes in runoff. It is shown how ta u(e) depends on lake geomorphology and climate, and for a number of la kes we calculate tau(e) values, ranging from 1.5 to 350 yr for closed lakes, and from 2.9 days to 2 yr for open lakes. We propose methods in volving Fourier analysis for inverting closed lake level or area recor ds to obtain plots of a simple aridity index C. It is shown that for a ll almost-equal-to 200 of the world's large (greater-than-or-equal-to 100 km2) closed lakes, satellite remote sensing of lake levels and are as is currently sensitive enough to monitor variations in C (e.g. in a verage basin precipitation) of order 1% to 10% on the time-scale of ye ars to decades.