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Delta blue intensity is a commonly used method to correct for the heartwood-sapwood color change in blue intensity (BI) measurements. It is based on the assumption that the heartwood-sapwood color change is similar in both earlywood and latewood. This assumption has not been supported physiologically. Furthermore, delta BI may confound the climate signals in earlywood and latewood BI as it is technically a linear combination of the other two. Here, instead of using delta BI, we used change point detection to identify the heartwood-sapwood transition, and corrected for the color change by rescaling the mean and variance of BI measurements after the transition to those immediately before. We tested three different change point detection methods and found that they agreed well with one another. Importantly, our approach preserves the climate signals in both earlywood and latewood BI data, while delta BI causes a total loss of climate signals in our test case. Therefore, we suggest that change point detection should be used instead of delta BI to account for the heartwood-sapwood color change. 

During summer 2010, exceptional heat and drought in western Russia (WRU) occurred simultaneously with heavy rainfall and flooding in northern Pakistan (NPK). Here, we use the Great Eurasian Drought Atlas (GEDA), a new 1,021 year tree-ring reconstruction of summer soil moisture, to investigate the variability and dynamics of this exceptional spatially concurrent climate extreme over the last millennium. Summer 2010 in the GEDA was the second driest year over WRU and the largest wet–dry contrast between NPK and WRU; it was also the second warmest year over WRU in an independent 1,015 year temperature reconstruction. Soil moisture variability is only weakly correlated between the two regions and 2010 event analogues are rare, occurring in 31 (3.0%) or 52 (5.1%) years in the GEDA, depending on the definition used. Post-1900 is significantly drier in WRU and wetter in NPK compared to previous centuries, increasing the likelihood of concurrent wet NPK–dry WRU extremes, with over 20% of the events in the record occurring in this interval. The dynamics of wet NPK–dry WRU events like 2010 are well captured by two principal components in the GEDA, modes correlated with ridging over northern Europe and western Russia and a pan-hemispheric extratropical wave train pattern similar to that observed in 2010. Our results highlight how high resolution paleoclimate reconstructions can be used to capture some of the most extreme events in the climate system, investigate their physical drivers, and allow us to assess their behavior across longer timescales than available from shorter instrumental records.