GVN330 Climate Data Analysis
Assignment 2.5: Daily Precipitation Distributions
You have previously examined the distribution of daily temperature records,
using histograms and cumulative frequency distributions. Daily temperature has
low skewness, so the distributions are relatively easy to visualize with graphical
tools.
Daily rainfall records, however, are usually highly skewed distributions; there
are many low (especially zero) values, and only a few high values. And daily
rainfall distributions in Sweden are less skewed than in many other parts of the
world!
The best way I have found to display daily precipitation distributions is a
cumulative frequency distribution graph with a logarithmic x-axis. In this
assignment, you will create such a graph in Matlab.
Reading
Wilks 3.3.7 – Cumulative Frequency Distributions (part of reading quiz 3)
If you are not familiar with the use of log-scales, I suggest the video at:
http://www.khanacademy.org/math/algebra/logarithms/v/logarithmic-scale
Exercises:
Ass2.5 Create seasonal cumulative frequency distribution (cfd) plots for daily
precipitation using the Saeve_daily.csv time-series.
a) Load the data into Matlab, and spit the precipitation into four seasons.
You can use a similar method to what you used in Ass2.3. As before, use data for
years 1961:2002, to avoid having too many NaNs.
c) Create the cumulative frequency distribution graph with cfd's for all seasons on
the same axis and a linear x-axis.
To create a cumulative frequency distribution plot, use the matlab function
cdfplot.
For this assignment, I would like you to create all the cfds on the same axes!
You saw in Ass2.4 how you style cdfplot using code such as:
h=cdfplot(winter);
set(h,'Color','c','LineWidth',3);
You also know how to put multiple cdfplots on the same axis using
hold on
before calling cdfplot again.
By default, cdfplot has a linear x-axis. Look at the result - it is very difficult to
draw any conclusions about the differences in the precipitation distributions for
each season!
d) Change the x-axis to be a logarithmic scale
You can change from log-scale to linear-scale using the command:
set(gca,'Xscale','log')
Discussion:
Now you should be able to answer questions such as:
 Which two seasons have the highest fraction of dry days (days with 0mm
rainfall)?
 Which is the driest season?
 Which is the wettest season?
 Is it true that summer has more dry days than winter, but also more days
with heavy (>20mm) precipitation?
Checkpoint – compare your answers with others!