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Stable isotopes in tree rings provide climatic information with annual resolution dating
back for centuries or even millennia. However, deriving spatially explicit climate models
from isotope networks remains challenging. Here we propose a methodology to model
regional precipitation from carbon isotope discrimination (Δ13C) in tree rings by (1)
building regional spatial models of Δ13C (isoscapes) and (2) deriving precipitation
maps from Δ13C-isoscapes, taking advantage of the response of Δ13C to precipitation in
seasonally dry climates. As a case study, we modeled the spatial distribution of mean
annual precipitation (MAP) in the northeastern Iberian Peninsula, a region with complex
topography and climate (MAP = 303–1086 mm). We compiled wood Δ13C data for two
Mediterranean species that exhibit complementary responses to seasonal precipitation
(Pinus halepensis Mill., N = 38; Quercus ilex L.; N= 44; pooling period: 1975–2008). By
combining multiple regression and geostatistical interpolation, we generated one
Δ13 C-isoscape for each species. A spatial model of MAP was then built as the sum of two
complementary maps of seasonal precipitation, each one derived from the corresponding
Δ13C-isoscape (September–November from Q. ilex; December–August from P.
halepensis). Our approach showed a predictive power for MAP (RMSE = 84 mm) nearly
identical to that obtained by interpolating data directly from a similarly dense network of
meteorological stations (RMSE = 80–83 mm, N= 65), being only outperformed when
using a much denser meteorological network (RMSE=56–57 mm, N=340). This method offers
new avenues for modeling spatial variability of past precipitation, exploiting the large
amount of information currently available from tree-ring networks.
This work was funded by the Marie Curie project SMARTREES (MC-ERG-246725, European Union, FP7), and Spanish project PALEOISOTREE (CGL2009-13079-C02-01). J.d.C. is supported by a FPI fellowship (MCINN, Spain). JPF is supported by the Ramón y Cajal programme (RYC-2008-02050, MCINN, Spain). |
