Changes in Land Surface Conditions on the Iberian Peninsula (1989 to 2004) Detected by Means of Time Series Analysis from Hypertemporal Remote Sensing Data

In the present study long-term variations (1989 to 2004) on the Iberian Peninsula are addressed using the "Mediterranean Extended Daily One Km AVHRR Data Set" (MEDOKADS). The Normalised Difference Vegetation Index (NDVI) was used as proxy for land surface response to precipitation variability and human activities with ecological and social impacts at various temporal scales. Despite large areas in Iberia were found to be progressively vulnerable to recent episodes of droughts and wild fires, changes in biomass productivity are more distinctly related to man induced land-use changes. To decide whether detected changes in surface reflectance are related to improvement or reduction in resource productivity a synoptically view of time-series analysis products derived from monthly NDV\´I data, including trend analysis, temporal shifts in the occurrence of the annual green peak, change detection in successive land-cover maps, and characteristics in the stochastic nature of the time-series, was selected. Changes in surface conditions detected at the 1 km scale cannot be understood without reference to physio-geographical and socio-economical data. The explanatory factors for changes in plant biomass productivity regionally differ across the Iberian Peninsula. Driving factors for increasing NDVI values are land abandonment and the negligence of silviculture, as well as modifications in land management schemes and the expansion of irrigation systems. Main explanations for negative trends are the exploitation of irrigation beyond mid-and long-term sustainability, wildfires, the depletion of biomass and vegetation cover by soil erosion, and the expansion of urban agglomerations.