9, but for tree-ring-reconstructed SPI for the 24-yr interval from 1568 to 1591 during the sixteenth-century megadrought. The most intense 10 years of the (c),(d) mideighteenth-century drought (1746–55) and the (e),(f) pre-Columbian pluvial (1483–92) are also mapped using SPI for the seasonal precipitation reconstructions. Tree-ring-reconstructed (a) cool-season (a) and (b) persistence-free warm-season SPI during the midnineteenth-century drought are averaged and mapped for the decade from 1855 to 1864. Regional average reconstructions are plotted for eight other subregions of North America in supplemental Fig. The black curve is a fitted spline emphasizing decadal variability. Tree-ring-reconstructed (a) cool- (DJFMA) and (b) warm-season (MJJpf) precipitation totals, plotted from 1400 to 2016 for the south-central United States (29°–39°N, 90°–100°W). 6, but for the Arctic Oscillation index averaged for May and June, correlated with (a) instrumental MJJ and (b),(c) reconstructed MJJpf precipitation totals. 4, but the similarity between instrumental and reconstructed patterns of ENSO correlation lends credibility to the reconstructions even in some areas without statistical validation from 1901 to 1927.Īs in Fig. Regions without reconstructed validation skill in the early-twentieth century are mapped in Fig. Four levels of significance are indicated by the contours ( p = 0.10, 0.05, 0.01, and 0.001). (c) As in (b), but for the precalibration period from 1872 to 1927 using tree-ring-reconstructed cool-season totals and the instrumental eMEI. The correlation between the November–February eMEI ( Wolter and Timlin 2011) and gridded (a) instrumental and (b) reconstructed cool-season precipitation totals for the period 1928–78. 4, but for the tree-ring reconstructions of warm-season (MJJ) precipitation totals. The calibration interval was 1928–78, and the validation interval was 1901–27 (calibration statistics: CRSQ = coefficient of multiple determination and CVRE = cross validation reduction of error validation statistics: VRSQ = Pearson correlation coefficient squared, VRE = reduction of error, and VCE = coefficient of efficiency).Īs in Fig. The calibration and validation statistics computed for the tree-ring estimates of cool-season (DJFMA) precipitation totals are mapped for the 6812 grid points over North America. The Spearman rank-order correlation computed between each chronology and the nearest GPCC precipitation grid point is mapped for (c) DJFMA and (d) MJJ totals. The type of chronology used is also indicated (EW is earlywood LW is latewood LW a is adjusted latewood RW is total ring width pRW is ring width with a prior-year warm-season signal). Site locations for (a) the 439 tree-ring chronologies that are discretely correlated with cool-season precipitation (DJFMA), and (b) the 547 chronologies discretely correlate with warm-season totals (MJJ). SEASONAL PRECIPITATION TOTALS FULLThe availability of instrumental precipitation measurements in the GPCC Full Dataset is illustrated for two decades in the early- and late-twentieth century by the median number of stations per 0.25° grid cell. macrocarpa), and (d) bald cypress ( Taxodium distichum). Four important tree species for seasonal precipitation reconstruction are illustrated, along with photomicrographs of their annual rings that display prominent variability in earlywood and latewood width: (a) blue oak ( Quercus douglasii), (b) ponderosa pine ( Pinus ponderosa), (c) bur oak ( Q.
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