Magdalena River Basin (Colombia)
The Magdalena catchment is characterized by tropical climate with dry and wet season cycle, small temporal variability and high spatial variability of daily average temperature values.
Daily and annual temperature in the Magdalena Basin is very constant. The average daily temperature ranges between 18.6 and 25.4 °C with a standard deviation of 0.74 and a mean of 21.8°C. The annual mean temperatures are also very constant (Figure 1). The linear trend computed for a period of 30 years (1979-2009) is a yearly decrease of 0.00002 °C. (Kraaijenbrink et al. 2014)
The high elevation differences in the Magdalena Basin, which range from the sea level to the highest point of 5.617 m a.s.l., result in a significant spatial variability of daily average temperature values. Temperature ranges from about 0 °C in the southern area where the Andan peaks overcome 4500 m a.s.l. m to 30 °C in lowland river plains in the northern area. (Kraaijenbrink et al. 2014)
Figure 1: Annual Average Temperature (ºC) 1976-2005.
(Source of DATA: IDEAM,2005. http://www.ideam.gov.co/web/siac/catalogo-de-mapas)
The Magdalena Basin is characterized by moderate precipitation, with an average rainfall of 2050 mm yr_1 for the whole basin.
Spatial precipitation patterns throughout the catchment vary greatly, from 500 mm yr_1 in the eastern mountains on the middle and upper basin to more than 5000 mm yr_1 in the western basin. The precipitation in the upper, middle, and lower reaches is 1535, 2185, and 1630 mm yr_1, respectively (Restrepo et al., 2006), (Figure 2).
The inter-annual cycle of rainfall is determined by the Intertropical Convergence Zone (ITCZ), which annually oscillates from the Equator to the northern Andes and back resulting in two rainy seasons: April–May and September–November. The dry season typically lasts from December into February and in July and August.
The seasonal intra-annual and inter-annual variability of rainfall is also linked to ENSO (El Niño Southern Oscillation). During intense El Niño events, the ITCZ can extend anomalously far south, bringing drought conditions to the Magdalena Basin as reported between 2014-2016. In January 2016, drought caused the Magdalena River to drop to 44 centimeters from an average minimum of two meters. The value was documented as record-low level. (Colombia’s Institute for Hydrology, Meteorology, and Environmental Studies, February 2016)
In contrast, La Niña events may cause intensive rains and lead to rainy periods that can last a year or longer (Angarita et al., 2018) as evidenced by the flood events between 2010-2013 in the lower basin (Hoyos, et al. 2013).
Figure 3: Total Annual Precipitation, 2012.
(Source of data: IDEAM http://www.ideam.gov.co/web/siac/catalogo-de-mapas)
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U.S. Agency for International Development (2017), ENV - Ecosystem-Based Adaptation in the Magdalena River Basin, https://www.usaid.gov/news-information/fact-sheets/env-ecosystem-based-adaptation-magdalena-river-basin.