1. INTRODUCTION
The hydrological cycle explains water distribution and its availability
across the globe. Processes such as evaporation, transpiration, and
precipitation connect the terrestrial and atmospheric components of the
hydrological cycle through water and energy exchange. Atmospheric
circulation allows regional-to-global water redistribution, establishing
teleconnections between remote areas. These teleconnections are vital
for the sustainability of ecosystems and biodiversity as well as for
water security, and socioeconomic development (Wagener et al., 2010;
Martinez & Dominguez, 2014; Swann, Longo, Knox, Lee, & Moorcroft,
2015; Molina, Salazar, Martínez, Villegas, & Arias, 2019).
Understanding moisture origin and the mechanisms driving atmospheric
transport is key for defining the interdependence of a territory with
its surroundings, and also for the definition of proper spatio-temporal
dynamics that determine regional atmospheric processes.
The conventional methods to identify moisture source regions, and to
estimate the proportion of incoming atmospheric moisture associated with
each source include i) analytical or box models, ii) numerical water
vapor tracers, and iii) physical water vapor tracers (Durán-Quesada,
Gimeno, Amador, & Nieto, 2010). The first two are
theoretical-computational models based on the Eulerian and Lagrangian
notion of trajectory, respectively. These models often use input
information from gauge stations and reanalysis data (Wang et al., 2004;
Fuka et al., 2014; Liu et al., 2020). The third method is based on
physical water vapor tracers in the isotopic composition of
precipitation. The interpretation of moisture tracers is useful to infer
the sources and the processes inducing fractionation in water isotopic
composition throughout the movement of air masses (Simpson & Herczeg,
1991; Martinelli, Victoria, Sternberg, Ribeiro, & Moreira, 1996; Clark
& Fritz, 1999). More specifically, the isotopic composition of
rainwater allows the interpretation of prevailing meteorological
conditions in the formation of air masses (temperature, humidity, wind
speed) and the origin of moisture (evaporation and/or transpiration)
(Gat & Carmi, 1970; Clark & Fritz, 1999; Duran-Quesada et al., 2010;
Gimeno, Drumond, Nieto, Trigo, & Stohl, 2010; Van der Ent, Savenije,
Schaefli, & Steele-Dunne, 2010; Gimeno et al., 2012). The study of
moisture sources through stable isotopes has been widely used in
understanding long-term changes in the water cycle and the dynamics of
climate (Gat & Carmi, 1970; Salati, 1979; Gat & Gonfiantini, 1981;
Clark & Fritz, 1999; Aggarwal, Froehlich, & Gat, 2005; Van der Ent et
al., 2010; Gimeno et al., 2012; Négrel, Petelet-Giraud, & Millot, 2016;
Sánchez-Murillo et al., 2016; Alexandre, 2020). However, the lack of
isotopic data in many locations around the world is still a disadvantage
for proper long-term analyses (Benjamin et al., 2005).
A current challenge for land and water resource managers is the
definition and understanding of the potential implications of
environmental change on the availability of water resources (Newman et
al., 2006; Gain et al., 2020; Rivadeneira et al., 2020). This challenge
has been generally addressed with local-scale management plans and
strategies. However, in a region like Northern South America
(particularly in Colombia), water, food and energy security (which
largely supports the country’s economy) depend, almost exclusively, on
surface water, which in turn is associated with short-term rainfall
generation processes (Álvarez-Villa, Vélez, & Poveda, 2011; Díaz,
Saurral, & Vera, 2020; Mesa, Urrea, & Ochoa, 2021). In addition,
Colombia is one of the most biodiverse regions in the world (Myers,
Mittermeier, Mittermeier, Da Fonseca, & Kent, 2000; Churchill, 2009;
Bruijnzeel, Scatena, & Hamilton, 2011; Herzog & Kattan, 2011;
Ehrendorfer, 2013; Hutter, Lambert, & Wiens, 2017; Hoorn, Perrigo, &
Antonelli, 2018; Bax & Francesconi, 2019). The connection with the
Pacific and Atlantic oceans, the Amazon-Andes interactions, and the
orographic barrier of the regional Andes are the major drivers of
atmospheric circulation and ecological diversity in the country
(Sakamoto, 2011; Hoyos, 2017; Poveda, Jaramillo, & Vallejo, 2014;
Espinoza et al., 2020). For biodiversity conservation, ecosystem health,
and socioeconomic development, the availability of water is an important
basis that depends on hydrologic functioning (Pringle, 2001). Therefore,
understanding the origin and dynamics of moisture that becomes rainfall
in the two most populated regions of the country is fundamental to
maintaining water security. Yet, these analyses have only been performed
with models that, to date, have not been contrasted with actual field
measurements such as those from environmental tracers.
In this study, we explore the hydroclimatic features underlying the
composition of Colombian atmospheric moisture by establishing the
isotopic baseline for the regional precipitation on a seasonal time
scale. We include data from 33 stations distributed along the
inter-Andean mountain region and the Caribbean region in Colombia,
available in the Global Network of Isotopes in Precipitation (GNIP)
project. We analyze the monthly variation of δ18O and
δ2H values, and the spatio-temporal reconstruction of
D-excess during 1971-2016. Comparing the Local Meteoric Water Line
(LMWL) with the Global Meteoric Water Line (GMWL) provides criteria of
depletion or enrichment of hydrogen and oxygen isotopic composition of
precipitation that, in turn, allow the identification of the oceanic or
terrestrial origin of air-water masses that effectively precipitates
over the target area. We use the results from the Lagrangian FLEXPART
model to contrast the information inferred from isotopic composition
with the regional moisture contributions structure based on the air
masses trajectories, providing a more comprehensive understanding of
moisture sources to the country and the potential implications of
alterations in these dynamics associated with land use and vegetation
cover change.