Investigation of flood inundation on playas within the Zone of Chotts, using a time-series of AVHRR

Our principal objectives were to examine the application of a time-series of advanced very high-resolution radiometer (AVHRR) data to contrast the inundation regimes of a range of large, climatically sensitive playas in the Zone of Chotts regions of southern Tunisia and northeastern Algeria. In doing so, we aimed to: (i) refine methods for monitoring monthly changes in lake areas and seasonal water balance, building from previous studies; (ii) explore the extent to which simple hydrological models can be developed for individual playas; and (iii) compare the hydrologic response of individual playas to seasonal rainfall inputs within North Africa. Here, analyses were conducted using two time-series of AVHRR data (c.2 images per month) for southern Tunisia and northern Algeria (1983-1993 and 1987-1999), with coincident meteorological data. These data were used to detect and monitor inundation events within specific playa catchments in the Zone of Chotts region. Key analyses methods included: (a) the use of reflectance profiles for each time-series to infer inundation processes for each playa and (b) the extraction of lake areas from sequential image data to determine the extent of inundation with an accuracy of between 2% and 6% (depending on lake size). For those playas which were found to inundate as a direct result of precipitation records of lake area change were used to drive simple hydrological models to allowed mean monthly precipitation (P), monthly effective precipitation (P-E), and monthly evaporation (E) to be estimated. The techniques presented here make an important contribution to our understanding of the hydrology of playas in this region. Results for individual playas also suggest that these techniques may be useful in highlighting the dynamic response of these environments to the forcing mechanisms for regional precipitation (e.g., North Atlantic Oscillation [NAO]). In addition, the findings suggest that more widespread monitoring of playa inundation processes in this manner may impact on our understanding of the precipitation/evaporation status of a number of dryland regions. (C) 2002 Published by Elsevier Science Inc.