DETERMINING AND APPLYING THE RESPONSE OF EPHEMERAL LAKES TO EXTREME FLOOD EVENTS USING EO Dr Robert G. Bryant and Michael P. Rainey SCEOS and Department of Geography, University of Sheffield, Winter Street, Sheffield S10 2TN, UK, Phone Number: +44 (0)114 222 7966, Fax Number: +44 (0) 114 222 7912 Email address:
[email protected] Abstract It is known that closed lake-volumes fluctuate in response to changes in evaporation and precipitation rates within their catchment basin. Measurement of lake-volume changes are, therefore, not only important for hydrological and economic purposes, but can also provide a climate record. By integrating the precipitation over the catchment basins, they can provide a fuller picture of precipitation changes than the more localised in situ measurements. Playas are common features of closed, arid basins, and are the most sensitive of closed systems to regional climate changes. However, as playa systems operate under a high-evaporation/low-rainfall regime (often > 20:1), hydrological changes are not generally expressed in terms of simple volumetric changes within a lake. Instead, playas record changes in terms of variations in the timing, magnitude, frequency and residence time of specific ephemeral flooding events; generally a much more complex response, that is less well understood Using a time-series of NOAA-AVHRR data (1979-present), and associated climate data for playas in southern Tunisia, appropriate methods are presented for the accurate monitoring and detection of ephemeral flooding within specific catchments. Results have led to a greater understanding of playa response to of these often-extreme events, and further analyses of specific large floods have shown that values of P-E (or the hydrologically effective precipitation, PE) can be estimated for specific dryland catchments by inverting a simple water-balance model allied to an EO-derived curve of basin volume against area.