Climate

The Rapel basins climate is classified as a Mediterranean climate. That type of climate has a well-defined annual cycle with the highest precipitation in austral winters and a drier period in austral summer (Alvial-Vásquez et al., 2020). Mean annual temperatures range between 16.5°C in the North and 10.5°C in the South.

Precipitation

Precipitation is higher on the coast due to clouds and in the Andes. The orographic effect increases precipitation along the Andes (DGA, 2004). Due to the topographic differences, mean annual precipitation ranges between 450 and 1050mm/year (Rojas et al., 2020). The highest precipitation falls in the winter season, between June, July, and August (DGA, 2004). The average monthly and annual precipitation is shown in Figures 5-6.

Figure 5-6: Mean monthly and annual precipitation, derived from CHIRPS V.2 for 1981 to 2020, plotted with Rstudio by Daniel Knopp.

The basin is also affected by El Niño and La Niña events. El Niño in Central Chile is associated with a considerable increase in precipitation and a decrease in temperature. In contrast, La Niña is associated with decreased precipitation and increased temperatures (Escobar & Aceituno, 1998). Read more about El Niño/La Niña

Consequently, precipitation has decreased significantly in central Chile in the last ten years, including in the Rapel basin. The last decade is also known as the Megadrought or the "permanent La Niña phenomenon". The lack of precipitation over the region causes water stress (CIREN, 2016).

References

Alvial-Vásquez, F., Abarca-del-Río, R., Ávila Andrés, I. (2020): High-Resolution Precipitation Gridded Dataset on the South-Central Zone (34° S–41° S) of Chile. In: Frontiers in Earth Science, 8(2020), DOI=10.3389/feart.2020.519975

DGA (2004): Diagnostico y clasificacion de los cursos y cuerpos de agua segun objetivos de calidad: Cuenca del Rio Rapel’.

Escobar, F. & Aceituno, P. (1998): Influencia del Fenómeno ENSO sobre la precipitación nival en el sector andino de Chile Central durante el invierno’. Available at: https://snia.mop.gob.cl/sad/MET1074.pdf [Accessed 27.06.2021].

Rojas, R.; Bennison, G.; Gálvez, V.; Claro, E.; Castelblanco, G. (2020): Advancing Collaborative Water Governance: Unravelling Stakeholders’ Relationships and Influences in Contentious River Basins. In: Water, Vol.12(2020), pp. 1-25, doi:10.3390/w12123316

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