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Understanding how precipitation isotopes vary spatially and temporally is important for tracer applications. We tested how well month‐to‐month variations in precipitation δ18O and δ2H were captured by sinusoidal cycles, and how well spatial variations in these seasonal cycles could be predicted, across Switzerland. Sine functions representing seasonal cycles in precipitation isotopes explained between 47% and 94% of the variance in monthly δ18O and δ2H values at each monitoring site. A significant sinusoidal cycle was also observed in line‐conditioned excess. We interpolated the amplitudes, phases, and offsets of these sine functions across the landscape, using multiple linear regression models based on site characteristics. These interpolated maps, here referred to as a sinusoidal isoscape, reproduced monthly observations with prediction errors that were smaller than or similar to those of other isoscapes. Sinusoidal isoscapes are likely broadly useful because they concisely describe seasonal isotopic behavior and can be estimated efficiently from sparse or irregular data.

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Naturally occurring isotopic variations in precipitation are used to trace water movement through landscapes and ecosystems. However, direct measurements are often unavailable, so many isotope‐based approaches to studying terrestrial processes require predicted isotopic inputs. We found that the isotopic composition of precipitation follows a predictable seasonal pattern. We developed a new approach for mapping precipitation isotope seasonality that will be useful in a wide range of fields.


This article was originally published in Geophysical Research Letters, volume 45, in 2018. DOI: 10.1029/2018GL077458


American Geophysical Union



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