Land Degradation Monitoring: Spectral Variability in a Semi-arid Mediterranean Ecosystem (natural Park Cabo De Gata-níjar, Spain)

The overall goal of this study is to develop remote sensing desertification indicators for drylands, in particular using the capabilities of imaging spectroscopy (hyperspectral imagery) to derive soil and vegetation specific properties linked to land degradation status. For this purpose, a hyperspectral (field and remote sensing) monitoring program was established in the Natural Park Cabo de GataNíjar in south-eastern Spain to: amonitor the landscape biological and ecological multitemporal changes; bidentify sources of variability in the spectra, in relation with the ecosystem dynamics; cdevelop physiologically and physically meaningful spectral indicators of change adapted to drylands specific reflectance signatures and environment. The Cabo de Gata-Níjar Natural Park presents a still-preserved semi-arid Mediterranean ecosystem that has undergone several changes in landscape patterns and vegetation cover due to human activity. Traditional land uses, particularly grazing, has favoured in the Park the transition from tall arid brush to tall grass steppe. In the past ~40 years, tall grass steppes and arid garrigues increased while crop field decreased, and tall arid brushes decreased but then recovered after the area was declared a Natural Park in 1987. Presently, major risk is observed from a potential effect of exponential tourism and agricultural growth. This paper presents observations and preliminary results from the spectral monitoring program, both at the field and at the remote sensing scale. INTRODUCTION Desertification is a land degradation problem of major importance in the arid regions of the world. Deterioration in soil and plant cover have adversely affected nearly 70 percent of the drylands as mainly the result of human mismanagement of cultivated and range lands. Combating desertification involves having an accurate knowledge on a current land degradation status and the magnitude of the potential hazard. As emphasized in the UN Convention to Combat Desertification, there is a need nowadays for more assessment of land degradation and desertification processes. Maps at the global, local, and regional scale of desertification status and hazards involve ground studies, high data requirements, erosion/desertification modelling, that make them rare and sparse. Current multispectral remote sensing data offer indices based on 2 to 3 band ratios that are used as proxy of the complex processes that take place in a degrading land, but are inherently limited. Thus, the knowledge on the current land degradation status of a land, or the magnitude of the potential hazard, is for the most part incomplete and fragmented. This makes it extremely difficult to design and implement mitigation, reclamation and prevention measures. In this context, GFZ dryland degradation program (in: Climate Variability and Human Habitat) aims at, with a thorough understanding of the global desertification processes, exploring the capabilities of imaging spectroscopy to derive soil and vegetation specific properties linked with land degradation status. The quantitative parameters to be determined from the hyperspectral data can be incorporated into erosion and dryland degradation models to monitor land degradation processes, assess land degradation status via the use of a globally applicable land degradation index, and © EARSeL and Warsaw University, Warsaw 2005. Proceedings of 4th EARSeL Workshop on Imaging Spectroscopy. New quality in environmental studies. Zagajewski B., Sobczak M., Wrzesień M., (eds) gain indicators for characterising specific surface properties related to water cycles, erosion processes, and plant productivity in drylands. Test sites were established in several vulnerable regions to determine the suitability of the procedures engaged: aA dry area in north-eastern Germany is being used to explore the relationships in a small catchment between spectral reflectance and rainfall runoff modelling; bIn the frame of the DeSurvey EU-IP (http://www.desurvey.net), advanced information extraction procedures are developed and tested to allow the determination of relevant soil parameters (e.g. organic matter content, soil iron content) from hyperspectral data; cThe Natural Park Cabo de Gata-Níjar in southern Spain (Almeria) encompasses a large range of land degradation processes, and provides an excellent study site to develop a hyperspectral monitoring desertification program. The project in Cabo de Gata is the focus of this paper. STUDY AREA The Cabo de Gata-Nijar Natural Park is a marine-terrestrial Park located in the Almeria province, SE Spain. The park covers 37570 ha of land and 12126 ha of marine coastline with altitudes ranging between 562 m high and 60 m under the sea level. The climate is Mediteranean semi-arid. The average annual rainfall between 1973 and 1996 at 43 m elevation was 193.9 mm, and the mean annual temperature was 19.4°C. The park is composed of two big features: the Cabo de Gata massif (Sierra del Gabo de Gata), and the coastal plain (Bahia de Almeria). The Cabo de Gata massif is the emerged section of a huge volcanic region which continues under the sea of Alboran and emerges in North Africa. This volcanic rock of the calco-alcaline type was formed during the Tertiary Era in four periods of hydrothermal activity between ca. 15 and 8 million years ago. Presently, there are about 3500 people living all year round in the park, including all the villages. Figure 1: Location of the Cabo de Gata-Nijar Natural Park. The square locates the area covered by HyMap in 2003 and 2004. The ecological importance of the park is in its volcanic origin, semi-arid climate, and marineterrestrial character, producing habitats such as Mediterranean steppe, dunes coastal formation, salt mines, cliffs, and marine prairies of fanerogamas. The Natural park biodiversity made it be classified in 1997 by the UNESCO as World Reserve of the biosphere. Soils are of two main types, calcareous or volcanic. Of more than 200,000 catalogues plant species in the Mediterranean area, the Cabo de Gata-Nijar Park contains about a thousand, a surprising number for such a small and fairly low lying area. The vegetal landscape is composed of various types of shrubland, ranging from tall arid brushes with species like the palmito (chamaerops humilis L. -considered the only native palm in the European continent), phlomix, to tall grass steppes of Stipa tenacissima L., arid garrigues (genista, artemisia), arid scrubs (thymus), opuntia (cactus), and crop fields. In Cabo de Gata-Nijar, the important social and economic changes in the last 50 years are that ~45% of croplands have been abandoned since 1957, and the area was proclaimed a Natural Park in 1987. A recent study on land cover changes between 1957 and 1994 has shown that land cover changes in the park underwent in the last 50 years two major processes. First, croplands Cabo de Gata-Níjar Natural Park