The water cycle and its phase changes are one of the most important components of the atmospheric energy cycle of the Earth. Furthermore, the available water builds the fundamental basis for the existence and diversity of the biosphere and of food production. Especially in arid or semiarid regions of the Earth the water budget and the available water are important factors because the ecosystem reacts very sensitive to small changes in precipitation and available water.
The Elqui valley in Chile at 30° S is located in the southern part of the arid north of Chile and in future the available water may become a critical factor because the populations in the valley is rapidly growing and the valley is more and more cultivated with irrigated plants. On the other hand the analysis of historical precipitation data shows that the precipitation between 30° S and 40° S is decreasing. Therefore the actual distribution of the energy- , and water balance components, as well as the soil moisture may become an important input for water management concepts of local authorities and for the new research centre ‘Centro de estudios avanzados en zonas aridas (CEAZA)’.
The aim of the project is to investigate the energy- and water balance as well as the climate of the Elqui valley, based on continuous surface measurements which were performed from 1999 to 2003 and on intensive measurements including radiosoundings which were performed in 2000, 2001 and 2002.

View of the Elqui valley

Surface measurement station at La Laguna/upper Elqui valley in the Andes	Surface measurement station at San Carlos/Elqui valley