24 25 In Chile, mediterranean climate conditions only occur in the Central Zone (ChMZ). 26 Despite its small area, this mediterranean climate region (med-region) has been 27 recognised as a hotspot for biodiversity. However, in contrast to the rivers of other med-

Thermal behavior of Mediterranean Andean streams in South-Central ChileDespite of the importance of temperature in the fluvial ecosystems, the knowledge of its spatial and temporal variability in Andean rivers is limited, thus it is necessary to clarify the relative importance of site-specific factors in controlling the temperature of rivers. The aim of this research was to characterize the thermal regime of five Andean streams through an altitudinal gradient. The results show that there is a spatial and temporal variability in water temperature with a relatively rapid rise in temperature in mid-December, being stable in January and February, and a rapid decrease at the beginning of March and April. The thermal heterogeneity recorded in the high Andean zone of the Biobio River Basin makes it clear that geomorphology characteristics of each site are important in regulating water temperature, associated mainly with the altitude and shade; this latter mainly generated by high mountains and in some cases by the timberline. It is known that thermal variability, mainly the maximum and minimum mean temperatures; causing severe stress on stenotherm organisms. Therefore, a deeper knowledge of the river temperature is essential for the management and future protection of the Andean freshwater ecosystems to mitigate the impacts associated to the global warming.