In a previous post, we illustrated a widely used method called principal component analysis (PCA). This method can be used as an exploratory tool to summarise a dataset made of hundreds or thousands of time series into just a few
Finding hidden patterns in the data using principal components analysis
In hydrology, it is frequent to analyse long time series coming from many sites. The figure below shows monthly streamflows at 207 sites in France for the period 1969-2014. Original data have been transformed to make the time series more
About the logo
The globXblog logo is a colourful doughnut that mimics an equaliser, referring to the sonification and visualisation part of the blog. In its core, a stormy icon represents the hydrological part of the blog. The equaliser is surrounded by a
Hydrology basics, episode 1: streamflow, precipitation and evapotranspiration
How does water end up flowing in rivers? As schematized below, it is the result of processes that have taken place in the river basin, also known as a catchment and delineated by a red line in the figure. For
Transforming a distance matrix into a map
The map in the figure below shows the location of 195 hydrologic stations, which can be used to explore the hydrologic regimes of Australian rivers. The hydrologic regime is characterized by the flow seasonality, as shown for three particular stations
El NiñOz
The Pacific Ocean sometimes catches a fever in its Eastern tropical part (off the coasts between Central America and Peru): for extended periods of time, its surface waters are abnormally warm. These are known as El Niño episodes. Sometimes the
Fun with dendrograms
A dendrogram is a way to visualise objects organised in a hierarchy. It looks like a tree where: the leaves represent the objects of the dataset; the branches link similar leaves according to a given criterion. Below are three animated
How Australian rivers can be grouped into 4 main hydrologic regimes
Investigating the hydrologic regime of 195 rivers in Australia revealed three types of flow seasonality. At some stations, the wettest period occurs during one particular season (winter or summer), whereas at others, similar flows are observed all year round. How
Exploring the hydrologic regime of 195 rivers in Australia
Plotting hydrologic regimes Most hydrologic studies start by determining the average quantity of water in rivers and how it is distributed throughout the year. Let’s consider the Australian reference dataset provided by the Bureau of Meteorology, with daily runoff data