In the course of our work at Digital Earth Africa we are always delighted when unexpected, positive outcomes present themselves to us. For Dr Meghan Halabisky, the Senior Science Advisor and Lead of the Product Development Task Team (PDTT) at Digital Earth Africa, such a serendipitous episode occurred when she found that Digital Earth Africa’s datasets extended into a tiny corner of Southern Spain. This presents exciting opportunities not only for the sharing of data but also, for Digital Earth Africa, a robust set of existing ground data that can be used for further validation.
Dr Halabisky has been collaborating with a Spanish wetland remote sensing researcher, Ricardo Diaz-Delgado who spoke about the famous Doñana wetlands where he works. Both researchers were intrigued to find that the Digital Earth Africa datasets actually cover this southernmost region of Spain.
The Doñana Wetlands are protected as a National Park and characterized by a mosaic of habitats, including marshes, lagoons, salt pans, and Mediterranean scrubland, which support a wide range of flora and fauna, especially migratory birds. The Doñana Wetlands have been recognized as a UNESCO World Heritage Site since 1994 and are considered one of the most important wetland ecosystems in Western Europe, playing a vital role in maintaining the region's ecological balance and biodiversity as well as supporting relevant economic activities (rice, berries, olive oil and citric crops, fisheries and tourism).
As with many of the world’s wetlands, critical challenges exist from which the highest threat is overexploitation of its underground waters, combined with urban and agricultural pollution, extreme climatic events and biodiversity loss due to wetlands lost. The wetland requires continuous ecological monitoring, and Earth Observation data plays a key role in monitoring water extent and quality, and the propensity and health of wetland vegetation. Doñana wetlands is also included in the eLTER Research Infrastructure as a Socio-Ecological Platform.
Dr Diaz-Delgado did some analyses and was able to compare Digital Earth Africa’s datasets to other datasets that exist for the Doñana, such as that provided by the Long-Term Ecological Monitoring Program also based on the Landsat time series of images available for the area since 1984.
Theil–Sen slope in days/year showing the hydroperiod trend from 1974 to 2021. Red indicates consistent and significant decreasing trend in hydroperiod, while blue indicates the opposite (methods from Díaz-Delgado et al. 2016). The boundary of Doñana National Park is shown in red
As the Digital Earth Africa datasets are based on the Mueller et al. (2016) algorithm using Landsat images, imagery strips include Southern Spain. The three available products that can be used in the area are: Daily Surface Water since 1984 for all available Landsat scenes over the area; an annual summary for mapped Water Surface, and; All-time Surface Water, provided in percent of wet over dry scenes.
Dr Diaz-Delgado explains that they provide yearly anomalies as a synoptic map to assess changes in natural inundation of Doñana marshes and water bodies (subtracting annual hydroperiod to the whole time series starting by 1984). But what is really revealing climate change and human actions is the hydroperiod time series spatial trend. Map of Doñana hydroperiod trend evidences the dramatic reduction of average hydroperiod in the last 5 years coincident with an extreme long drought in the region. The map also makes it possible to locate and assess the effects of specific management and restoration actions. The hydroperiod is the length of time and portion of year that a wetland holds ponded water. It is an important indicator for monitoring ecological trends and functions in wetlands given that it influences the types of aquatic plants and animals found in a wetland, as water availability is crucial for breeding, feeding, and sheltering.
The Digital Earth Africa datasets receive high praise from Dr Diaz-Delgado, and there are exciting opportunities for the pair of researchers to continue sharing the data and augmenting the maps and reports needed.