Use of rainfall data in checking temperature measurements

In this post I show how monthly rainfall data can be used to give additional confidence in monthly Tmax values that may otherwise be regarded as being incorrect or inconsistent with the regional climate. Analysis of rainfall data will play a major role in reconstruction of 19th century climates, partly because rainfall itself is a major part of climate and partly because the relative sparseness of early temperature data forces one to look further afield for confirmation. Differences in rainfall patterns may cause temperature homogenisation errors if such differences are not taken into account.

The figures below show raw data from Melbourne Regional Office (BoM id 86071). The red lines are time series of monthly Tmax anomalies (12 samples per year, January of year 1900 is placed at 1900.0); purely for display purposes the data are smoothed over 3 consecutive months. The blue curve (always above the blue zero line) shows monthly rainfall values in mm/100; multiply the values shown by 10 to get the monthly rainfall in centimeters.

1890 – 1900

CR08_RAIN1

In this period the most extreme Tmax values were associated with extremes of rainfall, low rainfall went with high Tmax, high rainfall with low Tmax.

1900 – 1910

CR08_RAIN2

Again there was an inverse relationship between Tmax and rainfall, especially in summer.

Breaking the blog prohibition on theoretical speculation by the author I’m going to suggest that cloudiness was the dominant driver of both Tmax and rainfall in summer in this part of Australia. However, theory will play no part  in climate reconstructions presented here, but rainfall plots will be used to guide quality-control and step-change adjustments of temperatures. If rainfall data is ignored some temperature extremes (such as the ones shown above) might be falsely corrected, or a persistent drought or rainy spell might trigger an invalid homogeneity adjustment.

Advertisements
This entry was posted in Uncategorized. Bookmark the permalink.

2 Responses to Use of rainfall data in checking temperature measurements

  1. David Hodge says:

    Hi,

    I have just found your blog. Fascinating stuff and I do hope you keep publishing. From curiosity, what tools are you using for your research? R, or something else.

    Like

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s