Precipitation isoscapes in areas with complex topography: Influence of large-scale atmospheric dynamics versus microclimatic phenomena

Abstract

While studies of the spatial distribution of precipitation isotope contents is well known at large scale and for more or less homogeneous areas, regions with complex topography and aerology are more sparsely or not at all documented. The aim of this research is to understand the factors influencing spatial/temporal changes of isotopes content in rainfall over a heterogeneous region. The region presents strong topographic contrasts, an insular context with varied weather exposure and subsequent microclimates. The approach consists in building 'isotopes landscapes (isoscapes)' for different months taking advantage of the 7 year-long monthly monitoring survey of the Corsica Network for Isotopes in Precipitation (CNIP, Corsica, France). Isoscapes use linear predictions based on multiple regressions of station-based precipitation isotope, climatic and topographic data. These regressions reveal the controlling effect of altitude (with a dichotomous pattern observed between the winter and the summer periods) and slope, while meteorological settings partially influence isotope contents. By explaining ∼88% of the δ18O spatial variability, isoscapes highlight both a controlling effect of local-scale meteorological circulation, and a contribution of micro-scale dynamics (due to topographic forcing), on the precipitation isotopes content. The analysis of residual values revealed that these two effects are not sufficient to explain the depletion in heavy isotopes. The deuterium-excess was used to investigate the influence of large-scale meteorological systems. Taking into account previous meteorological investigation, it was possible for the first time to hypothesize an influence of types of precipitation (convective or stratiform) on the rainwater isotopic composition in the study region. Finally, these results appear as evidence of the climate complexity in areas with steep reliefs and a potential limitation for generating reliable isoscapes in Mediterranean regions. They also demonstrate the role that isoscapes can play in documenting the microclimate processes in the world.