2. DATA AND METHODS
2.1 Study area
This research focuses on atmospheric moisture transport over central and
northern Colombia. The target region (Fig. 1) corresponds to the largest
hydrological system in the country, draining the Andes Mountain chain
towards the Caribbean Sea and encompasses two regions with marked
orographic differences: the Magdalena-Cauca River basin (Andean), and
the Caribbean regions. Due to their location, the oceanic influences in
the regional climate are characterized by the transport of moisture from
the Tropical and Subtropical Atlantic and Pacific Oceans, and
terrestrial sources from the Orinoco and Amazon basins, as well as local
recycling (Hoyos, 2017; Hoyos and Rodriguez, 2020).
[Insert Figure 1]
The Magdalena-Cauca River basin system is the major Andean catchment in
the country. It is characterized by a complex orography defined by the
division of the Andes into three branches, i) the western branch crosses
Colombia from south to north with approximately 1200 km in length,
parallel to the pacific coast, ii) the central branch between the Cauca
and Magdalena River valleys and iii) the eastern branch with an
extension of approximately 1500 km and heights up to 4500 meters above
sea level, towards the Amazon and Orinoco basins. The Magdalena River
flows in a Valley between the Eastern and central branches, and the
Cauca flows between the Central and Western branches. Their confluence
occurs at the lowlands that mark the transition to the Caribbean region.
The interaction between the large-scale circulation systems, the trade
winds, and the orographic systems results in differentiated climatic
regions over the territory.
The rainiest areas generally occur on the eastern slopes of the eastern
cordillera and the western slopes of the western cordillera, while
rainfall is lower (and more variable) in the inter-Andean valleys (Snow,
1975; Hoyos, Baquero-Bernal, & Hagemann, 2013). Likewise, the Amazon
region exports water vapor to the Andean and inter-Andean zones
generating high rainfall intensity, due to the ascent of trade winds and
the orographic effect of the Andes (Espinoza et al., 2020). The
distribution of precipitation in this region has significant spatial and
temporal variability (Poveda, Waylen, & Pulwarty, 2006; Hoyos et al.,
2013; Poveda et al., 2014; Espinoza et al., 2020). The most influential
seasonal event in the region is the migration of ITCZ that determines
the annual distribution of rainfall, characterized by a bimodal regime
with two wet seasons between March to May and September to November
(Giannini, Kushnir, & Cane, 2000; Alvarez-Villa et al., 2011; Espinoza
et al., 2020) and its interaction with the Atlantic and the Pacific
Ocean, the moisture contribution from the Caribbean Sea, and the Amazon
and Orinoco basins (Hoyos, 2017).
The Caribbean region, located in the northernmost portion of Colombia
(and South America), is low and flat in the north (except for the
occurrence of the Sierra Nevada de Santa Marta complex, a coastline
isolated mountain with a height of 5.7 km that influences local
atmospheric circulation in the North), in contrast with the southern
part of this zone, which is framed by the foothills of the Andes
Mountain range. The annual cycle of rainfall in this zone has a
different pattern from the Andes: a dry period from November to April
and a rainy period between May to October, explained by the ITCZ
migration, the occurrence of synoptic disturbances associated with the
Tropical Easterly Waves (TEWs), and the Caribbean Low-Level Jet (Poveda
et al., 2006; Arias, Martínez, & Vieira, 2015; Cárdenas, Arias, &
Vieira, 2017).