Results of data processing and maps making for distribution of meteorological parameters (T&P) and stable isotopes in meteoric waters (δ18O & δ2H) for the Baltic Sea catchment area

The catchment area of ​​the Baltic Sea is 1.75 million km2 (calculated according to [HELCOM Map and data service]), and its length from west to east is 1.65 ths. km, from north to south is 2.25 ths. km. he catchments of the largest rivers: Neva, Vistula, Oder (Odra), Neman, Western Dvina (Daugava), Narva, Kemijoki, Göta Älv occupy almost half of the catchment area. The climate of this area is influenced by large-scale atmospheric pressure systems – the Icelandic Low, the Azores High, and the winter high-pressure center (but summer low-pressure center) formed over Russia. The predominant westerly air masses bring moist and mild air from the Atlantic Ocean. Due to its large size, the climate varies across the drainage basin: subarctic in the eastern and northern parts, and maritime in the southwestern and southern parts [Assessment, 2008]. A set of regular grids and maps, including parameters of average annual air temperatures, annual precipitation amounts, signatures of stable isotope values ​​in meteoric waters, was constructed to understand regional spatiotemporal patterns that exist between the main climate parameters (temperature and precipitation, T&P), indicators of the isotopic composition (δ18O и δ2H) of meteoric waters and factors characterizing climate dependencies. Data from 521 weather stations (File: 01_MeteoStations_List.txt) located within and around the Baltic Sea catchment area (Sweden, Finland, Russia, Estonia, Latvia, Lithuania, Poland, Germany, Denmark, Norway, Belarus, Ukraine, Slovakia, Czech Republic, Austria) were used for climate maps making. The source of information on average monthly temperature and precipitation is the Pogoda&Klimat reference and information portal [Pogoda&Klimat, 2025]. Average monthly temperature and annual precipitation data were used as input data. Data from the Global Network on Isotopes in Precipitation (GNIP) [WISER] system and data of national projects were used to create isoscapes of δ18O and δ2H signatures in meteoric waters. The Baltic Sea catchment includes 38 stations that contribute data to the GNIP system. An additional 19 stations located around the catchment have been added to this set (File: 02_GNIPStations_List.txt). Isotopic δ18O and δ2H data are available for all stations, but δ2H data are missing for stations located in Sweden. Therefore, to isolinear maps making for deuterium, the data were reconstructed using the function of the dependence of δ2H values on δ18O, obtained from the regional line of meteoric waters for the Baltic Sea catchment area.The time period for constructing all regular grids and maps covers the range from 1961 to 2024, which provides a double climate cycle of 30 years. The GNIP data for each station represent a time series of δ18O and δ2H values ​​(with a step of 1 month) in cumulative monthly precipitation samples. A weighted average of the values ​​over the period (weighted proportionally to the amount of precipitation for a given month) was produced for spatial comparison of the data. Due to the significant distances between the stations and their uneven distribution, the first step was to perform a linear interpolation [Lam, 1983] of the δ18O and δ2H values ​​onto an intermediate irregular grid. The values ​​of the integrated deuterium excess index or d-excess or dxs (dxs = δ2Н – 8*δ18О), which depend on a number of external factors, were calculated based on averaged data. The averaged values ​​of meteorological parameters (mean annual temperature and annual precipitation) calculated for each point of the meteorological station, as well as the points of the condensed network of δ18O and δ2H values ​​in meteoric waters, were added to the corresponding point layers as attributes. Based on the specified meteorological data and data on the isotopic composition of meteoric waters (which cover the Baltic Sea catchment area and the adjacent territory), interpolation was carried out using the Natural Neighbor method [Beutel et al., 2010] and regular grids (with a cell size of 5x5 km) were constructed for the distribution of air temperature (File: 03_Temperature_GIRD.tif), precipitation (File: 04_Precipitation_GIRD.tif), stable isotopes δ18O and δ2H in meteoric waters (Files 05_Stableδ18O_GIRD.tif, 06_Stableδ2H_GIRD.tif), and the integrated d-excess index in meteoric waters (File: 07_DXS_GIRD.tif). The visual representation of spatial data in the form of figures is combined in the file 08_FiguresMaps.pdf.  This repository contains the following set of files:01_MeteoStations_List.txt – list of meteorological stations in the Baltic Sea catchment area and adjacent territory used to making of regular grids and maps of average annual air temperature and annual precipitation;02_GNIPStations_List.txt – list of GNIP stations in the Baltic Sea catchment and adjacent area used to making of regular grids and distribution maps of stable isotope values ​​δ18O and δ2H;03_Temperature_GIRD.tif – regular grid (geotiff) distribution of average annual air temperature values04_Precipitation_GIRD.tif – regular grid (geotiff) distribution of annual precipitation values05_Stable18O_GIRD.tif – regular grid (geotiff) distribution of stable isotope ​​δ18O values in meteoric waters06_Stable2H_GIRD.tif – regular grid (geotiff) distribution of stable isotope ​​δ2H values in meteoric waters07_DXS_GIRD.tif – regular grid (geotiff) distribution of integrated d-excess index values ​​in meteoric waters08_FiguresMaps.pdf – combined set of maps in the figures format: average annual air temperature, annual precipitation, distribution of stable isotope values ​​δ18O and δ2H, d-excess index