Ramzi Touchan

Wildfire is a fundamental Earth system process that has shaped terrestrial ecosystems, biogeochemical cycles, and human societies for millions of years. The Mediterranean Basin is one of the world’s major fire hotspots, where climatic extremes interact with dense human populations and long-standing land-use legacies, frequently resulting in severe wildfire activity. Nevertheless, the knowledge on the long-term history of Mediterranean fires has remained poor, and existing information is often difficult to access and reuse, with governmental documents, independent research groups, and numerous unpublished or inaccessible datasets. This lack of integration has limited our ability to detect wide-scale retrospective regional patterns, understand the drivers of fire occurrence, and place recent wildfire extremes within their historical context. Here, we present the Mediterranean Fire History Database (MedFireAtlas), the first openly accessible, standardised, region-wide compilation of long-term Mediterranean fire history data, designed to address this critical knowledge gap.The MedFireAtlas database integrates two types of data, covering different temporal resolutions and spanning both southern Europe and the North African regions of the Mediterranean Basin. The first type of data includes 43 site-level tree-ring-based fire history reconstructions spanning from the 13th century onward, mainly from forests characterised by surface-fire regimes. These datasets offer annually resolved and multi-century long information for surface-fire-adapted species, primarily Pinus nigra, as well as Cedrus atlantica and Pinus pinaster. The second type of data includes governmental documentary fire records, primarily covering the mid-20th century to recent decades, available through open or authorised sources. It contains over 1.8 million documentary records from a total of ten countries. All entries were harmonised under a common metadata structure, including location, date, cause (when available), burned area, and data type. End-to-end data architecture, workflows, quality-control procedures, and metadata guidelines within the database ensure consistency and reliability. The MedFireAtlas links detailed recent fire occurrences with multi-century historical reconstructions, enabling spatiotemporal analyses of fire regimes and regional patterns that are not possible using either data source alone.The key feature of MedFireAtlas is an interactive web interface built by R Shiny that enables users to visualise, filter and download fire data through a spatial interface. The platform provides full capabilities to investigate long-term temporal trends, country-level and regional patterns, and comparisons among multiple datasets, supporting scientific research and applied uses, providing valuable multi-century benchmarks for fire regime modelling and long-term ecological and climate research. The MedFireAtlas is designed as a living, community-driven resource: researchers and fire management agencies across the Mediterranean are encouraged to contribute their new or historical datasets. Overall, the MedFireAtlas establishes the first comprehensive database initiative for regional fire regime representing a critical step toward integrated, science-based fire management in one of the world’s most fire-prone and climate-vulnerable regions.

This report describes an international summer course, “Tree Rings, Climate, Natural Resources, and Human Interaction”, held in Cheriomushki, Russia, in the summer of 2018. The course was attended by 12 participants from six countries (Belgium, India, Lebanon, Poland, Russia, and South Africa) and instructors from the USA and included basic training in dendrochronology skills and dendroclimatology and dendroecology projects. This report focuses on a nested May–July Palmer Drought Severity Index (PDSI) reconstruction from annual rings of Pinus sylvestris trees growing in the region and also explores false-ring (FR) occurrence in samples collected during the course. Four chronologies, one developed during the course from Maina District, Khakassia, Russia, are used in the reconstruction, which was based on principal component (PC) regression. The nested reconstruction demonstrated a strong statistical relationship between PDSI and tree-ring growth and allowed for an assessment of climate variability on both interannual and interdecadal time scales. FR occurrence in tree cores collected along an elevational transect from a site along the Yenisei River north of Cheriomushki was found to differ depending on the position of trees on the slope. The frequency of FRs and the location of the FR within the annual ring also appear to be related to seasonal precipitation anomalies.

Annual river discharge is a critical variable for water resources planning and management. Tree rings are widely used to reconstruct annual discharge, but errors can be large when tree growth fails to respond commensurately to hydrologically important seasonal components of climate. This paper contrasts direct and indirect reconstruction as statistical approaches to discharge reconstruction for the Chemora River, in semi-arid northeastern Algeria, and explores indirect reconstruction as a diagnostic tool in reconstruction error analysis. We define direct reconstruction as predictions from regression of annual discharge on tree ring data, and indirect reconstruction as predictions from a four-stage process: (1) regression of precipitation on tree rings, (2) application of the regression model to get reconstructed precipitation for grid cells over the basin, (3) routing of reconstructed precipitation through a climatological water balance (WB) model, and (4) summing model runoff over cells to get the reconstructed discharge at a gage location. For comparative purposes, the potential predictors in both modeling approaches are the same principal components of tree ring width chronologies from a network of drought-sensitive sites of Pinus halepensis and Cedrus atlantica in northern Algeria. Results suggest that both modeling approaches can yield statistically significant reconstructions for the Chemora River. Greater accuracy and simplicity of the direct method are countered by conceptual physical advantages of the indirect method. The WB modeling inherent to the indirect method is useful as a diagnostic tool in error analysis of discharge reconstruction, points out the low and declining importance of snowmelt to the river discharge, and gives clues to the cause of severe underestimation of discharge in the outlier high-discharge year 1996. Results show that indirect reconstruction would benefit most in this basin from tree ring resolution of seasonal precipitation.

There is a lack of knowledge on how tree species respond to climatic constraints like water shortages and related atmospheric patterns across broad spatial and temporal scales. These assessments are needed to project which populations will better tolerate or respond to global warming across the tree species distribution range. Warmer and drier conditions have been forecasted for the Mediterranean Basin, where Aleppo pine (Pinus halepensis Mill.) is the most widely distributed conifer in dry sites. This species shows plastic growth responses to climate, being particularly sensitive to drought. We evaluated how 32 Aleppo pine forests responded to climate during the second half of the 20th century by using dendrochronology. Climatic constraints of radial growth were inferred by fitting the Vaganov–Shashkin (VS-Lite) growth model to ring-width data from our Aleppo pine forest network. Our findings reported that Aleppo pine growth decreased and showed the highest common coherence among trees in dry, continental sites located in southeastern and eastern inland Spain and Algeria. In contrast, growth increased in wetter sites located in northeastern Spain. Overall, across the Aleppo pine network tree growth was enhanced by prior wet winters and cool and wet springs, whilst warm summers were associated with less growth. The relationships between site ring-width chronologies were higher in nearby forests. This explains why Aleppo pine growth was distinctly linked to indices of atmospheric circulation patterns depending on the geographical location of the forests. The western forests were more influenced by moisture and temperature conditions driven by the Western Mediterranean Oscillation (WeMO) and the Northern Atlantic Oscillation (NAO), the southern forests by the East Atlantic (EA) and the august NAO, while the Balearic, Tunisian and northeastern sites by the Arctic Oscillation (AO) and the Scandinavian pattern (SCA). The climatic constraints for Aleppo pine tree growth and its biogeographical variability were well captured by the VS-Lite model. The model performed better in dry and continental sites, showing strong growth coherence between trees and climatic limitations of growth. Further research using similar broad-scale approaches to climate–growth relationships in drought-prone regions deserves more attention.

A nested July–June precipitation reconstruction for the period AD 1777–2012 was developed from multi-century tree-ring records of Pinus sylvestris L. (Scots pine) for the Republic of Khakassia in Siberia, Russia. Calibration and verification statistics for the period 1948–2012 show a high level of skill and account for a significant portion of the observed variance (>50%) irrespective of which period is used to develop or verify the regression model. Split-sample validation supports our use of a reconstruction model based on the full period of reliable observational data (1948–2012). Thresholds (25th and 75th percentiles) based on the empirical cumulative distribution of 1948–2012 observed precipitation were used to delineate dry years and wet years of the long-term reconstruction. The longest reconstructed dry period, defined as consecutive years with less than 25th percentile of observed July–June precipitation, was 3 years (1861–1863). There was no significant difference in the number dry and wet periods during the 236 years of the reconstructed precipitation. Maps of geopotential height anomalies indicate that dry years differ from wet years primarily in the location of an anomalous 500-mb ridge approximately over the study area.

The first large-scale network of tree-ring chronologies from the western Mediterranean (WM; 32°N–43°N, 10°W–17°E) is described and analyzed to identify the seasonal climatic signal in indices of annual ring width. Correlation and rotated empirical orthogonal function analyses are applied to 85 tree-ring series and corresponding gridded climate data to assess the climate signal embedded in the network. Chronologies range in length from 80 to 1129 years. Monthly correlations and partial correlations show overall positive associations for Pinus halepensis (PIHA) and Cedrus atlantica (CDAT) with winter (December–February) and spring (March–May) precipitation across this network. In both seasons, the precipitation correlation with PIHA is stronger, while CDAT chronologies tend to be longer. A combination of positive correlations between growth and winter–summer precipitation and negative partial correlations with growing season temperatures suggests that chronologies in at least part of the network reflect soil moisture and the integrated effects of precipitation and evapotranspiration signal. The range of climate response observed across this network reflects a combination of both species and geographic influences. Western Moroccan chronologies have the strongest association with the North Atlantic Oscillation.

Networks of tree-ring data are commonly applied in statistical reconstruction of spatial fields of climate variables. The importance of elevation to the climatic interpretation of tree-ring networks is addressed using 281 station precipitation records, and a network of 79 tree-ring chronologies from different species and a range of elevations in the eastern Mediterranean. Cluster analysis of chronologies identifies 6 tree-ring groups, delineated principally by site elevation. Correlation analysis suggests several of the clusters are linked to homogenous elevational moisture regimes. Results imply that climate stations close to the elevations of the tree-ring sites are essential for assessing the seasonal climatic signal in tree-ring chronologies from this region. A broader implication is that the elevations of stations contributing to gridded climate networks should be considered in the design and interpretation of field reconstructions of climate from tree rings. Finally, results suggest elevation-stratified tree-ring networks as a strategy for seasonal climate reconstruction.

The first large-scale network of 79 tree-ring chronologies in the Eastern Mediterranean and Near East (EMNE; 33°N–42°N, 21°E–43°E) is described and analyzed to identify the seasonal climatic signal in indices of annual ring width. Correlation analysis and cluster analysis are applied to tree-ring data and gridded climate data to assess the climate signal embedded in the network in preparation for climate field reconstructions and formal proxy/model intercomparison experiments. The lengths of the 79 combined chronologies range from 89 to 990 years. The monthly correlations and partial correlations reveal a pervasive positive association with May, June, and sometimes July precipitation, positive correlations with winter and spring (December through April) temperatures, and negative relationships with May through July temperature, although as expected, there are site-to-site exceptions to these general patterns. Cluster analysis suggests three groups of sites based on their association with climate. The chronologies for the EMNE have coherent seasonal precipitation and temperature signals across a fairly broad geographical domain. The predominant signal is a positive growth response to May–June precipitation. Collectively, the findings suggest that the network can be exploited to develop season-specific field reconstructions of precipitation and drought history in the EMNE.