Rainfall is a defining feature of Ireland’s climate, influencing agriculture, water resources, and everyday life across the country. During the winter months, rainfall patterns are strongly shaped by Atlantic weather systems, bringing frequent and sometimes intense precipitation. January is typically one of the wettest months of the year, making it particularly useful for examining how rainfall varies spatially across Ireland.
This blog explores patterns in January rainfall using long-term observations from 25 weather stations distributed across the country. By mapping median January rainfall values, the analysis highlights regional contrasts and provides insight into how Ireland’s geography and prevailing weather systems influence rainfall distribution Irish regions.
##Data used
This report uses historical monthly rainfall totals (mm) from 25 weather stations across Ireland, covering 1850–2014. Two datasets are used:
rain: monthly rainfall data with variables Year, Month, Rainfall, Station
stations: station metadata including latitude and longitude
These datasets have been provided through the GY672 course Moodle page and have made this analysis achievable. These datasets were downloaded and uploaded to R Studio and interpreted by using several codes to create a interpretive map
##Why January?
January was chosen for this analysis because it is typically one of the wettest months in Ireland. Rainfall during this period is strongly influenced by large-scale Atlantic weather systems, which produce widespread and persistent precipitation. As a result, spatial differences in rainfall between western, eastern, and inland regions are particularly clear. Data is also easier to comprehend in smaller pieces which is why it is more efficient to analyse each month individually rather than splitting the data into groups such as ‘winter’, ‘spring’, ‘summer’, and ‘autumn’.
##Load packages and data
library(tidyverse)
── Attaching core tidyverse packages ──────────────────────── tidyverse 2.0.0 ──
✔ dplyr 1.1.4 ✔ readr 2.1.5
✔ forcats 1.0.1 ✔ stringr 1.5.2
✔ ggplot2 4.0.1 ✔ tibble 3.3.0
✔ lubridate 1.9.4 ✔ tidyr 1.3.1
✔ purrr 1.1.0
── Conflicts ────────────────────────────────────────── tidyverse_conflicts() ──
✖ dplyr::filter() masks stats::filter()
✖ dplyr::lag() masks stats::lag()
ℹ Use the conflicted package (<http://conflicted.r-lib.org/>) to force all conflicts to become errors
library(leaflet)library(janitor)
Attaching package: 'janitor'
The following objects are masked from 'package:stats':
chisq.test, fisher.test
library(lubridate)
To complete this analysis, the above packages were used as they make it easier to work with large datasets, summarise rainfall patterns, and present the results in a clear and interactive way. Together, they allow the data to be organised, explored, and visualised on a map that helps reveal spatial differences in January rainfall across Ireland.
Load data saved as an RData file
load("rainfall.RData")
Confirm year range
range(rain$Year, na.rm =TRUE)
[1] 1850 2014
##Method
To examine typical winter rainfall patterns across Ireland, this analysis focuses on January rainfall records from 25 weather stations. The dataset was first filtered to include only January observations, ensuring that the analysis reflects consistent seasonal conditions across all years. For each station, the median January rainfall was calculated using data spanning the full period from 1850 to 2014. The code directly above is evidence of double checking the data span of 174 years is correct.
The median was chosen rather than the mean because it provides a more reliable measure of central tendency and reduces the influence of exceptionally wet or dry years that could otherwise skew the results. The resulting station level median rainfall values were then joined to geographic information containing the latitude and longitude of each station. These data were visualised using an interactive Leaflet map, with rainfall levels represented by color coded markers to allow spatial patterns to be explored easily.
The interactive map below allows users to explore spatial patterns in median January rainfall across Ireland. Each weather station is represented by a circular marker, with colors indicating different rainfall levels. Darker colors correspond to higher median rainfall values, while lighter colors represent drier locations.
Readers can zoom in to examine specific regions and click on individual stations to view the station name along with its median January rainfall. The legend provides context for the color scale, making it easier to compare rainfall levels between different parts of the country. This interactive approach allows patterns and regional contrasts to be explored more intuitively than would be possible using static figures alone. I recommend all readers who have taken an interest in this blog to immerse yourself into this study by exploring the interactive map above before continuing onto the discussion of patters and limitations of this analysis.
##Discussion of patterns
Map shows clear spatial variation in median January rainfall across Ireland. Stations located in the west and northwest generally experience higher median rainfall values, while many inland and eastern stations record considerably lower amounts. This pronounced west–east gradient reflects Ireland’s exposure to moist Atlantic air masses, which bring frequent rainfall to western coastal areas during the winter months.
As these air masses move eastward across the island, much of their moisture is lost, resulting in drier conditions in the east. Local topography further enhances this pattern, with upland and coastal regions experiencing greater rainfall due to uplift, while low-lying inland areas receive less precipitation, resulting in what locals call the ‘Sunny South East’ . January is typically one of the wettest months of the year in Ireland, and the patterns observed here highlight how both atmospheric circulation and physical geography combine to shape regional rainfall variability across the country. There is a visible contrast in the amount of precipitation experienced in the west of Ireland than there is in the east. This has remained consistent throughout each January analysed from 1850-2024.
Limitations
While the dataset spans a long historical period (174 years), the number of weather stations is limited, therefore some regions may be underrepresented. The west and the south of Ireland have more weather stations than the more northern and midland areas. This could potentially be one of the reasons that more rainfall has been accounted for t=in these regions. Additional weather stations could only enhance this analysis and aid future studies in this area. Future analyses may also chose to explore seasonal comparisons or temporal trends to provide a more detailed understanding of rainfall variability across Ireland.
##Conclusion
This analysis has demonstrated clear and consistent spatial patterns in median January rainfall across Ireland using long-term observations from 25 weather stations. The interactive map highlights a strong west–east contrast, with higher rainfall levels in western and northwestern regions and drier conditions across much of the east and inland areas. These patterns reflect the combined influence of Atlantic weather systems and Ireland’s physical geography.
By focusing on median January rainfall, this blog provides a robust representation of typical winter conditions while reducing the influence of extreme events. The use of interactive mapping allows these spatial patterns to be explored in an intuitive and engaging way, making the results more accessible to a wider audience. Overall, this study illustrates how long-term climate data can be used effectively to reveal regional environmental patterns and deepen understanding of Ireland’s rainfall distribution.