Examing and Comapring Observed Monthly Rainfall From 1850 to 2014 for Four Irish Stations: Dublin Airport, Belfast, University College Galway and Cork Airport.
Author
Laura Cullinane, 20334131
Introduction
Examining rainfall is a key factor when looking at changes in the climate. When assessing rainfall it can be used to look at the effect that climate change is having on an array of different systems such as the water cycle and water balance vital for water management and planning (Mét Eireann, n.d.).
Historical observations are crucial for understanding past climate and change. By examining long-term historical rainfall observations, extreme events can be identified, as well as trends and patterns in rainfall and weather. These records contribute to the running of climate models to predict potential future climates and aid in risk assessment for future policy-making, planning, and infrastructure (Murphy et al., 2018).
This report examines the use of the R package ‘Dygraphs’ on rainfall data for four different stations to represent the Island of Ireland from 1850 to 2014 to examine and compare the difference in observed rainfall.
Data and Methods
The data set used for this analysis was rainfall.Rdata. This data comes from the original Island of Ireland Precipitation network (Noone et al., 2015) which contains 25 weather stations across Ireland. The data set used in this report contains monthly data and runs from the year 1850 to 2014 continuously with no missing data. It contains two objects, rain and stations.
To provide the most accurate view possible of the observed rainfall for Ireland, four of twenty-five stations were chosen to represent Ireland. Dublin Airport, Belfast, University College Galway and Cork Airport were chosen to create a time series of monthly rainfall data in Ireland that would best represent all sides of the country.
The main package used in this report is the dygraphs package. This package allows the user to create interactive time series plots, with the ability to add a RangeSelector to scroll through the time series and select a specific time frame (R.Studio.github, n.d.).
The following methods were used to create dygraphs of the monthly January rainfall time series for the chosen stations in a combined manner and as four individual stations.
The respective working directory was chosen and the following packages were loaded to analyse the rainfall dataset.
Warning: package 'dygraphs' was built under R version 4.4.2
library(tidyverse)
Warning: package 'tidyverse' was built under R version 4.4.2
Warning: package 'ggplot2' was built under R version 4.4.2
Warning: package 'dplyr' was built under R version 4.4.2
Warning: package 'lubridate' was built under R version 4.4.2
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✔ lubridate 1.9.3 ✔ tidyr 1.3.1
✔ purrr 1.0.2
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✖ dplyr::filter() masks stats::filter()
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ℹ Use the conflicted package (<http://conflicted.r-lib.org/>) to force all conflicts to become errors
Once the packages were loaded, then the data set ‘rainfall.RData’ was loaded into R in order to carry out the analysis on the monthly rainfall series.
The following code creates a subset of the rain data for four locations that have been filtered from the main data set: Dublin Airport, Belfast, University College Galway and Cork Airport only. The data is then summarised, and a new data frame is created with the variables: Year, Month and Rainfall.
Rainfall data is pulled and a time series is created starting in January 1850, on a monthly basis, for each station. Once created, the results from each station were assigned to new variables: dub_st, bel_st, ucg_st and cork_st.
The last two lines of the code for this section combine the rainfall time series created for the four stations using ‘cbind’. This combines the four stations into one time series. The last line of code for this section establishes a subset of the time series for the four stations for a specific time frame. Using ‘window()’, data for January 1850 to July 1850 were extracted, with the results shown in the table below.
bel_ts dub_ts ucg_ts cork_ts
Jan 1850 115.7 75.8 108.9 155.3
Feb 1850 156.4 112.0 163.8 359.5
Mar 1850 157.2 80.3 174.9 216.2
Apr 1850 107.2 74.7 152.8 191.3
May 1850 116.2 101.1 133.1 157.0
Jun 1850 16.1 11.3 33.9 9.9
Jul 1850 72.5 58.4 111.9 174.9
Results
Using the combined time series ‘beldubucgcork_ts’, a dygraph was created, producing a combined station interactive time series plot with a RangeSelector. Each station is represented by its own coloured line as seen in Figure 1. It can be seen that the time series runs from 1850 to 2014 and showcases the monthly rainfall data at each location. In Figure 1, a visible decrease in rainfall can be observed in the late 1800s and an increase in the amount of rainfall can be seen from the mid-1900s.
Figure 1: This figure displays a dygraph with combined multiple time series for four locations: Dublin Airport, Belfast, University College Galway and Cork Airport, for the observed monthly rainfall from 1850 to 2014. The dygraph contains an interactive range selector to move through the data and select specific time frames within the data set.
To examine the four stations on an individual level, a dygraph for each station from 1850 to 2014 was created using the code below. A range selector was added at the bottom of the dygraphs. Each plot displays individual observed January rainfall, where some similar and different trends can be observed at all the stations. Each dygraph displays increases and decreases in observed rainfall. Cork and Galway show more observed rainfall in comparison to Belfast and Dublin.
Figure 2: Individual dygraphs for each station, Dublin Airport, Belfast, University College Galway and Cork Airport for the observed monthly rainfall from 1850 to 2014. Below the final plot, a range selector allows the selection of specific time frames within the data set.
Discussion
The results shown in Figure 1 display increasing and decreasing trends in the monthly rainfall. During the mid-1800s, there is a high amount of monthly rainfall, it is then seen to dip and even out gradually towards 1900 and gradually increases again in the mid-1950s to 2014. When using the range selector the highest rainfall can be observed in Cork in 2005.
Figure 2 shows the four different dygarphs for each station. It can be observed that Dublin and Belfast have the lowest levels of rainfall, only exceeding 200mm of rainfall on a small number of occasions. University of Galway exceeds 200 mm on multiple occasions and Cork Airport displays the highest rainfall out of all the stations, with observed rainfall over 300mm and 400mm occurring several times from 1850 to 2014.
The main reason for the difference in observed rainfall for the stations, is how Ireland’s climate is influenced by the Atlantic Ocean and the North Atlantic Drift. The coasts closest to the Atlantic Ocean experience more extreme weather, in this case rain, as seen on the West Coast of Ireland in the Galway and Cork stations. The influence of the Atlantic Ocean decreases as it moves inland, the presence of different topographic features reduces the impact the Atlantic conditions have on the East side of the country, as seen in Belfast and Dublin stations (Mét Eireann, n.d.).
It can be noted in both Figure 1 and Figure 2 that rainfall has increased significantly since the 1950s compared to 1850-1900. This may be a result of a warming climate as a result of anthropogenic-induced climate change. The warmer the atmosphere, the greater the amount of moisture the atmosphere holds thus leading to increased levels of rainfall (Teagasc, 2024). Ireland’s climate has warmed, which in turn has caused wetter periods from 1960 onwards (Teagasc, 2024), as seen in both the figures.
Conclusion
Rainfall in Ireland has varied greatly from 1850 to 2014. A visible decrease and increase can be seen in all dygraphs. It was observed that certain locations across Ireland display different measurements of observed rainfall that coincide with station location and topography. Stations on the west side of the country experienced higher levels of observed rainfall and stations on the east side of the country experienced less. Even though there is a great difference in observed rainfall between the east and the west of Ireland, the increase in climate change and continued intensive use of fossil fuel is increasing sea temperature causing more evaporation thus resulting in more rainfall for all locations across Ireland.
Sources
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R.Studio.github, n.d. dygraphs for R. [Online]
Available at: https://rstudio.github.io/dygraphs/
[Accessed 2024].
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