Past and Future Drought Variability in the Mediterranean Basin

PROJECT SUMMARY (NSF-Grant AGS-Paleo Perspectives on Climate Change Program 1103314)

The Mediterranean Basin and southwestern United States have been identified by general circulation models (GCMs) as regions of high sensitivity of climate to increasing greenhouse gases. The proposed research addresses the long-term climate variability of the Mediterranean Basin from a combined analysis of climatic data and tree-ring data. A network of drought-sensitive tree-ring chronologies in the Mediterranean Basin (latitudes 25º-42º N and longitudes 10º W-43º E) will be analyzed for information on long-term climate variability, associated atmosphere-ocean anomalies, and the ability of GCMs to reproduce important drought-related features of regional climate. The work blends existing chronologies from the Mediterranean region with development of new chronologies from currently under-sampled parts of North Africa to generate a Mediterranean Basin Drought Atlas (MBDA) that chronicles spatiotemporal drought variability over the past few centuries to millennium. Reconstructions will include seasonal precipitation, Palmer Drought Severity Index, and net precipitation. The reconstructions will be analyzed for relationship of droughts and wet periods to atmospheric circulation and sea-surface temperature (SST) anomalies. Drought patterns of the past will be placed in context of climate-change projections from GCMs.

Intellectual Merit:

Refined knowledge and understanding of the full range of past hydroclimatic variability over North Africa and other parts of the Mediterranean Basin is critical for improved understanding of factors driving that variability and handling of low-frequency climate variability by GCMs. The proposed research is the first effort at assembling and interpreting networks of tree-ring chronologies for this purpose in the region. The research team includes a lead PI (Touchan) largely responsible for the collection, development and dissemination of the existing tree-ring network over much of the region; the PIs are experienced in climate-field reconstruction and interpretation. The synthesis effort proposed will exploit the rich resource of recently-developed tree-ring data for improved estimates of potential near-term future hydroclimatic variability and explore novel methods of time series analysis to place current and future hydroclimatic variability in a long-term context. The analysis of climatic and paleoclimatic data will help identify linkages of Mediterranean climate variability with large-scale patterns of atmospheric and oceanic variability. The field reconstructions of climate variables will facilitate probabilistic forecasts of hydroclimate change on the interannual-to-multidecadal timescale that account for both radiatively-forced climate change and natural variability; such forecasts can be a basis for assessing future risk and developing adaptation strategies.

Broader Impacts:

The proposed work will improve and update the climate history of the Mediterranean basin, and provide a baseline for assessing past and future drought. A regional societal benefit is improved resource management and lessened environmental degradation in Mediterranean countries. The proposed MBDA will complement the ongoing Old World Drought Atlas’ (OWDA), the existing ‘North American Drought Atlas’ (NADA) and the ‘Monsoon Asia Drought Atlas’ (MADA) — nearly completed now as part of a National Science Foundation project on “Tree-Ring Reconstructions of Asian Monsoon Climate Dynamics”. In doing so, the MBDA will greatly expand the coverage of gridded drought reconstructions across the Northern Hemisphere to allow for more complete synoptic-scale comparisons of hydroclimatic variability at annual-to-centennial time scales. The tree-ring chronologies and derived field reconstructions will serve the climate-modeling community as a paleoclimatic “target” dataset for evaluating performance of GCMs. The proposed research will help integrate research and education by developing the scientific and human resources in the region. Students, scientists, and natural resource managers in the region will be exposed to the science of dendrochronology and its practical applications through workshops, meetings and participation in field work. Essential to the proposed work are the local collaborators who will be involved in diverse aspects of the research. The collaboration will foster development of local scientific efforts and the exchange of students and between the USA and Mediterranean countries.