HYDROPERIOD OF DONANA MARSHES: NATURAL OR ANTHOPIC ORIGIN OF INUNDATION REGIME?

摘要

There is a major concern on current restoration and management programmes being applied over Donana Ramsar Site. Historical inundation regime has been largely changed according to human transformations. On site measurements along short and recent periods have provided scant local information on inundation variability. Historical inundation patterns on a spatial basis are necessary to understand short and long time effects of human transformations on natural regimes. By compiling a long time series of Landsat MSS, TM and ETM images (1975-2006) we have mapped inundation levels for every available scene over Donana wetlands. After coregistration, radiometric correction and time series normalization, we applied the best semiautomathic method for discriminating inundation levels according to ground-truth data. Then, we reconstructed for each hydrological cycle the hydroperiod value for every pixel. The value is calculated as the minimum number of days detected as flooded for the available dates during every cycle. Results reveal a significant increase on the average number of days inundated for the whole marsh and local hydroperiod changes related to human transformations and rainfall variability. Hydroperiod maps are therefore helping to understand hydrological implications of future management decisions.