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Monitoring drought conditions in the Iberian Peninsula using moderate and coarse resolution satellite data

F. Javier García-Haro(1), Fernando Belda(2), M. Amparo Gilabert Navarro(1), Joaquín Meliá(1), Alvaro Moreno(1), David Poquet(2), Ana Perez-Hoyos(1) and Demetrio Segarra(1)

(1) University of Valencia, Dr. Moliner 50, 46100 Burjassot, Spain
(2) Instituto Nacional de Meteorología, Apartado de Correos 22043, 46071 Valencia, Spain

Abstract

DULCINEA – “methodology to retrieve vegetation parameters from the synergistic use of new generation satellite sensors. Application to monitoring extreme climatic events in the Iberian Peninsula”– project is being developed under the framework of Spanish National Research Program. The objective of the project is to provide coherent estimates of biophysical variables such as fractional vegetation cover (FVC) and leaf area index (LAI) at regional and global scales. An essential element of the project strategy is to provide sensor-independent estimates by exploiting the synergy from medium and coarse resolution imaging instruments. In order to achieve this goal, time series from an ensemble of operational medium (MERIS) and coarse (VEGETATION, MODIS, SEVIRI) resolution imaging instruments have been obtained. The datasets were interpolated into a same geographic and temporal reference frame. The analysis has evaluated the complementary information offered by these products due, among other factors, to the differences in the frequency of observations and the spectral and spatial sensor characteristics. Adapted variants of a probabilistic spectral mixture analysis (SMA) algorithm which is currently used operationally in the context of LSA SAF have been developed to derived time series of FVC and LAI. The spatial and temporal consistency of the biophysical parameters has been demonstrated. These variables can provide a direct indicator of vegetation biomass, structure and condition on a regional scale. The potential of derived biophysical variables in the field of drought conditions monitoring is assessed. In particular, the vulnerability of natural ecosystems against the effects of climate fluctuations like drought and extreme events in the Iberian Peninsula has been analysed, from the correlation between the retrieved parameters and climatic variables. Iberian Peninsula is suffering from its worst drought in decades, which has lead to devastating economic losses in many parts of the region and has increased concern about the summer fire season, particularly in the western areas. The study was focused on semi-areas that are thought to be undergoing large, rapid changes at the present time and are prone to desertification processes. In this work, highly accurate monthly climatic maps of precipitation and temperature during the 1950–2007 period were calculated by using all the stations provided by the Instituto Nacional de Meteorología (INM) of Spain. The Standardised Precipitation Index (SPI) was calculated to quantify and monitor the precipitation deficit distributions. The SPI calculation for any location is based on the long-term precipitation record for a desired period. Both the soil moisture conditions and the vegetation activity respond to precipitation anomalies on a relatively short scale. For this reason, values within the “Extreme Drought” category were monitored both spatially and temporally using the SPI calculated for a 3–month time scale. High correlations have been found between SPI and satellite-derived vegetation products in different semi-arid regions. The climatic disturbances affect both the growing season and the total amount of vegetation. Differences in the timing of the vegetation response to cumulative lagged precipitation were evident among the vegetation formations examined. Nevertheless, the impact of climate variability on the vegetation dynamics has shown not to be the same for every region. The moderate resolution of the Full Resolution MERIS reflectance imagery has allowed us to address the influence of the land use, structure and composition of the vegetation. The results of this study indicate that retrieved biophysical variables capture well the vegetation variability on seasonal and inter-annual time-scales and are meaningful to analyze the interaction between vegetation and climate.

 

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry