Assessment and monitoring water stress condition of arid vegetation using remote sensing techniques. The Atacama Desert (Chile) case

Water stress assessment of natural vegetation plays a key role in water management of arid ecosystems. It allows scientists and managers to relate water extraction rates with changes in vegetation water condition, and consequently, to define safe water extraction rates for maintaining a healthy ecosystem. This is particularly important for conservation of rare and endangered species in arid and hyperarid ecosystems as related to the importance of water resources for human consumption and industry. Atacama desert in Northern Chile constitutes an excellent case study due to the importance of water management for supplying water to mining industry and population and for protecting endangered species.

Several studies have shown that remote sensing constitutes a powerful tool for assessing water stress condition of plant populations due to its capability of quantitatively estimating important parameters related to plant water condition, such as evapotranspiration, biomass and foliage water content. However, water stress assessments of arid plant species is difficult to perform for several reasons. First, vegetation is distributed in small patches within vast areas; therefore its identification, water condition description and monitoring is costly and technically hard to achieve. Second, natural dynamics of many species is unknown, and consequently potential responses to water stress could be unpredictable and highly variable. Finally, arid plant species are adapted to live under water scarcity, therefore symptoms produced by water stress take a long time to be evident, making early detection and monitoring difficult.

The objective of this study is to analyze the usefulness of remote sensing for assessing water condition of natural vegetation spots in arid ecosystems, and to propose a methodology to identify and to monitor water stress effects induced by exogenous perturbations. The Tamarugo forest (Prosopis tamarugo Phil.) in the hyperarid Atacama desert, Northern Chile, will be used as a study area. Tamarugo is an endemic specie of the Atacama desert with a limited distribution and it is completely dependent on groundwater supply.

Modern satellite images -high spatial and spectral resolution- as well as different remote sensing analysis techniques will be explored to assess water condition of the Tamarugo forest. Ground measurements of the forest water condition will be carried out to validate the remote sensing analysis. In order to identify water condition patterns -observed in modern satellite images - in historical satellite images, the use of different up-scaling  techniques will be analysed. Natural dynamic of vegetation and anthropogenic disturbances will be studied using time series of Landsat (1986-2012) and MODIS (2003-2012) satellite datasets and environmental variables. Finally, the knowledge and techniques developed in this research will be analysed in the context of an operational water management project or an environmental impact assessment.