The problem of constructing millennia-long tree-ring chronologies from overlapping segments of cross-dated ring-width series is reviewed, with an emphasis on preserving very low-frequency signals potentially due to climate. In so doing, a fundamental statistical problem coined the 'segment length curse' is introduced. This 'curse' is related to the fact that the maximum wavelength of recoverable climatic information is ordinarily related to the lengths of the individual tree-ring series used to construct the millennia-long chronology. Simple experiments with sine waves are used to illustrate this fact. This is followed by more realistic experiments using a long bristlecone pine series that is randomly cut into a number of 1000-, 500-and 200-year segments and standardized using three very conservative methods. When compared against the original, uncut series, the resulting 'chronologies' show the effects of segment length even when the most conservative and noncommittal method of tree-ring standardization is applied (i.e., a horizontal line through the mean). Alternative schemes of chronology development are described that seek to exorcise the segment length curse. While they show some promise, none is universal in its applicability and this problem still remains largely unsolved.

Two reconstructions of spring (May-June) precipitation have been developed for southwestern Turkey. The first reconstruction (1776-1998) was developed from principal components of nine chronologies of Cedrus libani, Juniperus excelsa, Pinus brutia, and Pinus nigra. The second reconstruction (1339-1998) was derived from principal components of three J. excelsa chronologies. Calibration and verification statistics of both reconstructions indicate reasonably accurate reconstruction of spring precipitation for southwestern Turkey, and show clear evidence of multi-year to decadal variations in spring precipitation. The longest period of reconstructed spring drought, defined as consecutive years with less than 80% of normal May-June precipitation, was 4 years (1476-79). Only one drought event of this duration has occurred during the last six centuries. Monte Carlo analysis indicates a less than 33% probability that southwestern Turkey has experienced spring drought longer than 5 years in the past 660 years. Apart from the 1476-79 extended dry period, spring droughts of 3 years in length have only occurred from 1700 to the present. The longest reconstructed wet period, defined as consecutive years with more than 120% of normal May-June precipitation, was 4 years (1532-35). The absence of extended spring drought during the 16th and 17th centuries and the occurrence of extended wet spring periods during these centuries suggest a possible regime shift in climate. Preliminary analysis of links between large-scale climatic variation and these climate reconstructions shows that there is a relationship between extremes in spring precipitation and anomalous atmospheric circulation in the region.

Two millennia-length juniper ring width chronologies, processed to preserve multi-centennial growth trends, are presented for the Alai Range of the western Tien Shan in Kirghizia. The chronologies average the information from seven near-timberline sampling sites, and likely reflect summer temperature variation. For comparison, chronologies are also built using standard dendrochronological techniques. We briefly discuss some qualities of these ''inter-decadal'' records, and show the low frequency components removed by the standardization process include a long-term negative trend in the first half of the last millennium and a longterm positive trend since about AD 1800. The multicentennial scale Alai Range chronologies, where these trends are retained, are both systematically biased (but in an opposite sense) in their low frequency domains. Nevertheless, they represent the best constraints and estimates of long-term summer temperature variation, and reflect the Medieval Warm Period, the Little Ice Age, and a period of warming since about the middle of the nineteenth century.

A 1000 year reconstruction of cool-season (November-April) precipitation was developed for each climate division in Arizona and New Mexico from a network of 19 tree-ring chronologies in the southwestern USA. Linear regression (LR) and artificial neural network (NN) models were used to identify the cool-season precipitation signal in tree rings. Using 1931-88 records, the stepwise LR model was cross-validated with a leave-one-out procedure and the NN was validated with a bootstrap technique. The final models were also independently validated using the 1896-1930 precipitation data. In most of the climate divisions, both techniques can successfully reconstruct dry and normal years, and the NN seems to capture large precipitation events and more variability better than the LR. In the 1000 year reconstructions the NN also produces more distinctive wet events and more variability, whereas the LR produces more distinctive dry events. The 1000 year reconstructed precipitation from the two models shows several sustained dry and wet periods comparable to the 1950s drought (e.g. 16th century mega drought) and to the post-1976 wet period (e.g. 1330s, 1610s). The impact of extreme periods on the environment may be stronger during sudden reversals from dry to wet, which were not uncommon throughout the millennium, such as the 1610s wet interval that followed the 16th century mega drought. The instrumental records suggest that strong dry to wet precipitation reversals in the past 1000 years might be linked to strong shifts from cold to warm El Niño-southern oscillation events and from a negative to positive Pacific decadal oscillation.

May-July Standardized Precipitation Index (SPI) for the land area of most of Turkey and some adjoining regions are reconstructed from tree rings for the period 1251-1998. The reconstruction was developed from principal components analysis (PCA) of four Juniperus excelsa chronologies from southwestern and south-central Turkey and is based on reliable and replicable statistical relationships between climate and tree ring growth. The SPI reconstruction shows climate variability on both interannual and interdecadal time scales. The longest period of consecutive drought years in the reconstruction (SPI threshold ≤−1) is 2 yr. These occur in 1607-1608, 1675-1676, and 1907-1908. There are five wet events (SPI threshold ≥+1) of two consecutive years each (). A 5-yr moving average of the reconstructed SPI shows that two sustained drought periods occurred from the mid to late 1300s and the early to mid 1900s. Both episodes are characterized by low variability.