Tracing Water Sources and Fluxes in a Dynamic Tropical Environment: From Observations to Modeling

Abstract

Tropical regions cover approximately 36% of the Earth's landmass. These regions are home to 40% of the world's population, which is projected to increase to over 50% by 2030 under a remarkable climate variability scenario often exacerbated by El Niño Southern Oscillation (ENSO) and other climate teleconnections. In the tropics, ecohydrological conditions are typically under the influence of complex land-oceanatmosphere interactions that produce a dynamic cycling of mass and energy reflected in a clear partition of water fluxes. Here, we present a review of 7 years of a concerted and continuous water stable isotope monitoring across Costa Rica, including key insights learned, main methodological advances and limitations (both in experimental designs and data analysis), potential data gaps, and future research opportunities with a humid tropical perspective. The uniqueness of the geographic location of Costa Rica within the mountainous Central America Isthmus, receiving moisture inputs from the Caribbean Sea (windward) and the Pacific Ocean (complex leeward topography), and experiencing strong ENSO events, poses a clear advantage for the use of isotopic variations to underpin key drivers in ecohydrological responses. In a sequential approach, isotopic variations are analyzed from moisture transport, rainfall generation, and groundwater/surface connectivity to Bayesian and rainfall-runoff modeling. The overarching goal of this review is to provide a robust humid tropical example with a progressive escalation from common water isotope observations to more complex modeling outputs and applications to enhance water resource management in the tropics.

Isotopic composition and major ion concentrations of national and international bottled waters in Costa Rica

“…1 B). Purified, Spring, and Not Specified bottled waters exhibited depleted δ 18 O values, confirming the strong bias and industry preference towards Pacific-type water sources [9] . Deuterium excess values ranged from + 4.2‰ up to + 17.0‰, with a mean value of + 11.0‰, which are in the range of rainfall across Costa Rica [7] , [8] , [9] , [10] , [11] .…”

“…Overall, all samples exhibited a strong meteoric origin [7 , 8] . Based on available isoscapes of Costa Rica and recent monitoring efforts [7] , [8] , [9] , only 4 bottled waters were in the range of typically enriched Caribbean-type water -2‰ to -4‰ in δ 18 O; Fig 1 A), while 41 samples revealed Pacific-type δ 18 O compositions (ranging from -6 up to -11‰; Fig. 1 B).…”

Chirripó hydrological research site: Advancing stable isotope hydrology in the Central American Páramo

“…The unique geographic location of Costa Rica within this mountainous region, with moisture inputs from the Caribbean Sea (windward) and the Pacific Ocean (complex leeward topography), offers an ideal scenario for the use water stable isotopes to develop hydrological research (S anchez -Murillo, Esquivel-Hern andez, Birkel, et al, 2020b). The first isotopic characterization of the surface water system of CHRS indicated that the evaporation conditions in the glacial lakes are highly influenced by input from precipitation that is in isotopic equilibrium with local water vapour, yielding low evaporation to inflow ratios (<20%, Esquivel-Hern andez et al, 2018).…”

Chirripó Hydrological Research Site: advancing stable isotope hydrology in the Central American Páramo

“…The Central American region is transected by a NW-SE mountain range that divides the region into the Caribbean and Pacific slopes with similar precipitation regimes (Sanchez-Murillo et al, 2020a). The unique geographic location of Costa Rica within this mountainous region, with moisture inputs from the Caribbean Sea (windward) and the Pacific Ocean (complex leeward topography), offers an ideal scenario for the use water stable isotopes to develop hydrological research (Sanchez-Murillo et al, 2020b).…”