Long-Term Monitoring of the Flooding Regime and Hydroperiod of Doñana Marshes with Landsat Time Series (1974–2014)

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 . 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 ( < 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 < 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.

Fast and Automatic Data-Driven Thresholding for Inundation Mapping with Sentinel-2 Data

“…The average annual rainfall is 550 mm, with an interannual variation ranging from 170 mm (2004)(2005) to 1000 mm (1995)(1996). A diagram of the long-term average rainfall over the study area is provided in Díaz-Delgado et al [2]. Rainfall occurs mainly from October-April, and the dry season is between May and September.…”

“…Flooded areas are variable in depth, turbidity and vegetation cover, being driven mainly by the amount and seasonal pattern of rainfall. These seasonal marshes constitute the largest flooded surface in the Doñana wetlands and are breeding and wintering habitat for many species of European water birds [2]. On the aeolian sand deposits that close the mouth of the Guadalquivir River, there is an extensive system of temporary ponds [34].…”

“…Hydroperiod is a critical parameter that shapes the distribution of aquatic plants and animals and determines the habitat available for many of the living organisms, including migratory and endemic water birds, in the marshland [2,49].…”

“…The approach used for the generation of the Landsat inundation maps is described in detail in Díaz-Delgado et al [2] and relies on Landsat band 5 (Short-Wave Infrared (SWIR)). Resulting inundation maps have a coarser spatial resolution than the product of the Sentinel-2 that is evaluated in this study.…”

“…Several approaches in the literature aiming to identify shallow inundated wetland areas rely on the low reflectance values of water in the SWIR band, since it is less sensitive to sediment-filled waters and therefore more suitable for delineating the boundaries between water and dry ground in shallow wetland areas [2,41]. Hence, the unsupervised approach is based on the selection of a threshold on SWIR (Band 11) of S2.…”