Typology of calendar years as a tool for substantiating the adaptation of forestry in the Leningrad region to climate change

This article presents a retrospective analysis of climate changes in the territory of St. Petersburg and Leningrad region for the period from 1836 to 2025 based on a unique monthly data series. Unlike traditional approaches that rely on the analysis of average values, a method for discrete typology of calendar years using the k-means clustering technique was proposed, with four stable clusters identified according to a complex of hydrothermal indicators. Using nonparametric Mann-Kendall, Sen’s estimator, and Pettitt tests, an irreversible transition of the region into a new climatic era (Era III) has been proven, characterized by the predominance of extremely hot (80% frequency) and extremely wet (70% frequency) years. Points of bifurcation of the climate system have been identified (1988 for temperature, 1993 for precipitation). The inefficiency of preserving spruce monocultures under new conditions has been justified, and priority directions for adapting forestry have been proposed: changing the dominant tree species, transitioning to regulated hydro-forest improvement, and updating safety sanitary norms.

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