Abstract
This paper presents a semi-automatic procedure to discriminate seasonally flooded areas in the shallow temporary marshes of Doñana National Park (SW Spain) by using a radiommetrically normalized long time series of Landsat MSS, TM, and ETM+ images (1974–2014). Extensive field campaigns for ground truth data retrieval were carried out simultaneous to Landsat overpasses. Ground truth was used as training and testing areas to check the performance of the method. Simple thresholds on TM and ETM band 5 (1.55–1.75 μm) worked significantly better than other empirical modeling techniques and supervised classification methods to delineate flooded areas at Doñana marshes. A classification tree was applied to band 5 reflectance values to classify flooded versus non-flooded pixels for every scene. Inter-scene cross-validation identified the most accurate threshold on band 5 reflectance (ρ < 0.186) to classify flooded areas (Kappa = 0.65). A joint TM-MSS acquisition was used to find the MSS band 4 (0.8 a 1.1 μm) threshold. The TM flooded area was identical to the results from MSS 4 band threshold ρ < 0.10 despite spectral and spatial resolution differences. Band slicing was retrospectively applied to the complete time series of MSS and TM images. About 391 flood masks were used to reconstruct historical spatial and temporal patterns of Doñana marshes flooding, including hydroperiod. Hydroperiod historical trends were used as a baseline to understand Doñana’s flooding regime, test hydrodynamic models, and give an assessment of relevant management and restoration decisions. The historical trends in the hydroperiod of Doñana marshes show two opposite spatial patterns. While the north-western part of the marsh is increasing its hydroperiod, the southwestern part shows a steady decline. Anomalies in each flooding cycle allowed us to assess recent management decisions and monitor their hydrological effects.
Highlights
Doñana temporary marshes are one of the largest protected wetlands in Europe with an extent of340 km2, of which 300 km2 are included in the Doñana National Park
We chose a classification tree as the most accurate according to high Kappa and global accuracy and low variance
We evaluated interannual variation on hydroperiod dynamics by estimating the time series mean hydroperiod from 1974 to 2014 and calculating mean hydroperiod from 1974 to 2014 and calculating the the hydroperiod anomalies per flooding cycle (Figure 7)
Summary
Doñana temporary marshes are one of the largest protected wetlands in Europe with an extent of. 340 km , of which 300 km are included in the Doñana National Park. The dominant clay and silt substrates of Doñana marshes are soaked with the first showers and a shallow water layer (0.51 m average water column) spreads over the floodable area (Figure 1, solid blue area). Average water column) spreads over the floodable area (Figure 1, solid blue area). Evaporation becomes most important factor in and the hydrological balance and the marshes dry up most important factorthe in the hydrological balance the marshes dry up almost completely by the almost completely the end of July. During groundwater plays an important role in end of July
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