Reconstruction of past hydroclimate variability in Iran from a multi-centennial and multi-parameter juniper tree-ring network

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The suggested project aims to establish a multi-parameter juniper tree-ring network over the climate-sensitive semiarid Iran to reconstruct natural hydroclimate variability over the past centuries at annual resolution. The investigated tree-ring parameters include tree-ring width (TRW), stable oxygen isotope variations in tree-ring cellulose (18OTRC,) and quantitative wood anatomical features (QWA), from which ecological adaptations in the drought resilience of Iranian junipers will be evaluated. Since the various tree-ring parameters are sensitive to different climate variables over the seasonal cycle, drought events occurring in different seasons and due to different climatic reasons can be identified. Since the network approach integrates tree-ring sites from climatically contrasting regions over Iran that are influenced by different air moisture sources, it enables us to detect variations in the strength of major atmospheric circulation patterns and their impact on hydroclimate variations and extreme hydrological events over Iran. Special emphasis lies on an in-depth analysis of long-term variability of the frequency, intensity, and duration of extreme hydroclimatic events on different time scales from years to decades and centuries. Backward trajectory modelling will be applied to identify regional differences in dominant atmospheric moisture origins and related atmospheric flow patterns over the tree-ring network in selected pointer years. This procedure will allow us to detect changes in moisture transport pathways leading to extreme climate events in different parts of Iran over the past ca. 40 years. Existing juniper 18OTRC chronologies from neighboring areas in West-Central Asia will be combined with our data to study large-scale teleconnections between hydroclimatic signals originating from regions dominated by the westerly winter precipitation regime versus the Asian summer monsoon system. In doing so, temporal shifts in the strengths of these two important circulation systems and their impact on drought risk in Iran can be identified.