The role of fog, orography, and seasonality on precipitation in a semiarid, tropical island

Abstract

Isotopes of water (2H/1H and 18O/16O) are commonly used to trace hydrological processes such as moisture recycling, evaporation loss, and moisture source region and often vary temporally in a given region. This study provides a first‐ever characterization of temporally variable precipitation mechanisms of San Cristóbal Island, Galápagos. We collected fog, rain, and throughfall samples over three field seasons to understand the mechanisms driving seasonal‐ and event‐based variability in the isotopic composition of precipitation in Galápagos. We establish that fog is a common phenomenon in San Cristóbal, especially during the dry season, and we found that fog, compared with cocollected rainfall, is consistently enriched. We further suggest that the relative contribution of fog formed via different mechanisms (orographic, advective, radiation) varied seasonally. We found that the source region is the most dominant control of the isotopic composition of rainfall in the Galápagos at both the seasonal and event scales, but subcloud evaporative processes (the nontraditional manifestation of the amount effect) became a dominant control on the isotopic composition of rainfall during the dry season. Overall, our findings suggest that understanding seasonally variable water‐generating mechanisms is required for effective water resource management in San Cristóbal Island and other semiarid island ecosystems under current and future regimes of climate change.

Global Isotope Hydrogeology―Review

“…These meteoric waters are not captured by current precipitation isotope monitoring networks and may represent important terrestrial water inputs in some regions (Kaseke et al, ). In some areas, fog drip waters contribute to recharge (e.g., Aravena et al, ; Ingraham & Matthews, ; Kaseke et al, ; Schmitt et al, ; Scholl et al, ; Zhan et al, ). Widespread importance of fog drip waters to recharge remains unconfirmed, yet this potential source of recharge should be considered in some settings. High‐elevation recharge and subsequent sampling from wells or springs at lower elevations can lead to lower‐than‐expected δ 18 O values in groundwater (section ).…”

Orographic distillation and spatio‐temporal variations of stable isotopes in precipitation in the North Atlantic

“…Water samples collected in March and July 2015 from Sphagnum spp. and from throughfall show isotopic enriched values similar to other studies summarized by Scholl et al () and Schmitt, Iregui‐Riveros, and Hu (), which compared isotopic values for fog to rain events (Figure ). The throughfall isotopic composition is close to the seawater isotopic value collected 3‐m depth at 11 km from Terceira Island east coast on July 2012, suggesting a near water vapour source with minimal evolution of the vapour mass and slight mixing in the troposphere.…”

Governance Mechanisms and Barriers for Achieving Water Quality Improvements in Galapagos

“…Community involvement and participation of all social actors to secure the effectiveness of an integrated water resource management plan is recommended for all three islands. Involving communities in all stages of decision making such as policy and plan formulation and project and program implementation (bottom-up approach) encourages local stakeholders to work together and provides capacity building and empowerment opportunities to communities [64][65][66]. Local stakeholders are considered experts of their local environment.…”