This week’s post is on rainfall analysis using data from weather stations in The Gambia between 1984 and 2014. The data used is collected from 14 weather stations in The Gambia and these stations are found in different regions. Data was not available for the Kanifing and Kuntaur LGAs because of the unavailability of a weather station in these two regions. With the exception of Sibanor and Njau which recorded 30 years, rainfall data was collected for 31 years from 1984 to 2014 for all the other stations. The table below shows the LGAs and weather stations.
Table 1: LGAs with weather stations
|Brikama||Jambajelly, Sibanor and Yundum|
|Kerewan||Kerewan, Kaur and Bakendik|
|Janjangbureh||Janjangbureh, Njau and Sapu|
|Basse||Fatoto, Naude and Basse|
This post concentrates on the length of the rainy season nationally over time; to see whether the rainy season has become shorter and whether The Gambia experienced a dropped in the amount of rainfall during this time period.
Table 1 shows the average monthly rainfall across decade, looking at the ranges of years in which The Gambia experienced the highest amount of rainfall. The variable years is categorized into three sets with an interval of 10 years. The table indicates that The Gambia recorded the highest amount of rainfall between the years 2004 to 2014, seconded by 1994 to 2003 and then 1984 to 1993. We learnt from the table that the amount of rainfall has increased in current years that is from 2004 to 2014 as compared to the other two decades. The table also shows that the month August recorded the highest amount of rainfall across all sets of years
Table 2: Average monthly rainfall across decades
Figure 1 is a scatter plot of average rainfall by decade showing clearly the pattern of rainfall from 1984 to 2014. The graph contains three types of colors. The blue dots record the average amount of rainfall in 1984 to 1993, the red dots indicate the average amount of rainfall in 1994 to 2003 and finally, green show the average amount of rainfall in 2004 to 2014. The scatter plot indicates that the years 2004 to 2014 recorded the highest amount of rainfall. The graph shows that in all the three sets of years, the month August recorded the highest amount of rainfall. In 2004 to 2014, it is seen from the graph that the Gambia experienced a bit of rainfall in May. This shows that during this time period the Gambia had six months rainfall as compared to the years 1994 to 2003 where the rainy season lasted for five months and 1984 to 1993 the rainy season was for four months. Thus, this shows that the length of the rainy has increased in recent years.
Figure 1: Average monthly rainfall by decade
Figure 2: Variation in the amount of rainfall for rainy months
The box plot of Figure 2 shows that from 2004 to 2014 the average rainfall in August is 300mm which is higher than the average rainfall recorded for August in the other two decades. We learnt from the figure that there is not much variation in the amount of rainfall recorded for the month of June across all decades. In 1994 to 2003 the month of October recorded the highest amount of rainfall as compared to the amount recorded for October in the other two decades.
Our next post will be to breakdown the rainfall numbers by weather station to see whether this pattern applies to all areas measured, or whether there are exceptional weather stations compared to the national trend observed these past 30+ years.