The spatial variation of soil water isotopes (SWI) - representing the baseline for investigating root water uptake (RWU) depths with water stable isotope techniques - has rarely been investigated. Here, we use spatial SWI depth profile sampling in combination with unmanned aerial vehicle (UAV) based land surface temperature estimates and vegetation indices (VI) in order to improving process understanding of the relationships between soil water content and isotope patterns with canopy status. We carried out a spatial sampling of ten SWI depth profiles in a tropical dry forest. UAV data were collected and analyzed to obtain detailed characterization of soil temperature and canopy status. We then performed a statistical analysis between the VI and land surface temperatures with soil water content and SWI values at different spatial resolutions (3 cm to 5 m). Best relationships were used for generating soil water isoscapes for the entire study area. Results suggest that soil water content and SWI values are strongly mediated by canopy parameters (VI). Various VI correlate strongly with soil water content and SWI values across all depths. SWI at the surface depend on land surface temperature (R² of 0.65 for δ18O and 0.57 for δ2H). Strongest overall correlations were found at a spatial resolution of 0.5 m. We speculate that this might be the ideal resolution for spatially characterizing SWI patterns and investigate RWU. Supporting spatial analyses of SWI with UAV-based approaches might be a future avenue for improving the spatial representation and credibility of such studies.

The Colombian Andean Mountains host the headwaters of the main basins of the country. However, the interactions between high-mountain ecosystems and the isotopic composition of water in this region has been poorly studied. Here we present and analyze the first set of stable isotopes data collected in the Central Andes of Colombia. Stable isotopic composition of stream water and precipitation was determined for a period between 2017 and 2018 in the Upper Claro River Basin. The driving factors influencing the spatial and temporal variability of δ 2H, δ 18O and d-excess were identified and compared to daily air temperature and precipitation at seven meteorological stations. A Local Meteoric Water Line was defined as δ²H = 8.13 δ 18O + 12.5, R 2=0.98. δ 2H, δ 18O and d-excess values of precipitation were more negative during the rainy season and changes were more related to precipitation events and amounts than to temperature. An altitude effect of -0.11 ‰ / 100 m and -0.18 ‰ / 100 m was estimated for stream water and precipitation, respectively, where the latter showed a non-linear behavior. The data set was compared to stations of the Global Network of Isotopes in Precipitation (GNIP) database in Colombia and a back-trajectory analysis of air masses was conducted to compare with d-excess. δ 18O weighted means changed with respect to the position of the Central Andes and the altitudinal range 2,100 to 3,100 m a.s.l.. High d-excess can be attributed to moisture recycling enhanced by the local ecosystems and the travel of precipitable water from the Amazon basin across the northern Andes. The results showed a high range of variation due to the differences in elevation, seasonality and atmospheric circulation patterns across the year. The present study contributes to fill the gap of spatial and temporal isotopic composition data in the northern Andes as well as to the implementation of the first “National Network for Isotopes” in Colombia.