# Documentation of Reused Data

**Dataset Name:** ERA5-Land monthly temperature time series for Lower Oder monitoring sites
**Version:** 1.0
**Description**: Monthly air and skin temperature time series extracted from the ERA5-Land reanalysis for the grid cell nearest to each monitoring site in the Lower Oder River system. 
The dataset spans 1950–2025 and contains monthly mean temperature (meanT) and monthly maximum temperature (maxT) at 0.1° × 0.1° spatial resolution.

## 1\. Source Information

**Original Source:** Copernicus Climate Change Service (C3S), ERA5-Land: Monthly averaged reanalysis by hour of day.

**URL/DOI:** https://doi.org/10.24381/cds.68d2bb30

**Citation:**
Copernicus Climate Change Service (C3S). (2019). ERA5-Land monthly averaged data from 1950 to present. Copernicus Climate Data Store (CDS). DOI: 10.24381/cds.68d2bb30.

## 2\. Data Collection Details

**Collection Method:** ERA5-Land is a climate reanalysis generated by ECMWF, combining a land-surface model with assimilated observations. Values represent model-derived estimates rather than in-situ measurements.

**Extraction Method:** For each monitoring site, the nearest ERA5-Land 0.1° × 0.1° grid cell was identified via geographic proximity, and monthly values were extracted for the full 1950–2025 period.

**Geographic Location:** Lower Oder River basin, Germany–Poland border region.

**Temporal Coverage:** 1950–2025

## 3\. Data Structure

- **Data Type:** `Quantitative`
- **Format:** `CSV`
- **File Structure:** `Each row corresponds to a unique site–month aggregated observation. Variable names and units are defined in the accompanying data_dictionary.csv.`

## 4\. Access and Use Conditions

**License:** Copernicus Data Licence (free, open, attribution required).

**Restrictions:** Users must cite the Climate Data Store (CDS) and the ERA5-Land DOI.

## 5\. Data Quality and Validation

**Quality Assurance Procedures:**

Nearest-grid-cell extraction applied consistently across all monitoring sites, using the `extract` function within R's terra package.

**Known Issues:**

Coarse spatial resolution (~9 km) may smooth local microclimatic variability near river corridors.
Model–observation discrepancies may occur where land cover or elevation differ between the grid cell and the actual sample location.

## 6\. Contact Information

**Dataset Curator:**
Paula Torre Zaffaroni Department of Ecohydrology and Biogeochemistry Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB), Berlin, Germany paula.torre.zaffaroni@igb-berlin.de
(ORCID 0000-0002-1007-843X)

## 7\. Data Provenance

**Transformations and Analyses:** Spatial nearest-neighbour matching to monitoring sites; further calcuation of monthly mean and maximum temperature statistics.

**Record of Changes:**
v1.0 (2025-11-03): Initial extraction and harmonisation performed for external analysis.

## 8\. Additional Notes
When reusing the data, please cite both the ERA5-Land dataset and the associated manuscript.