Increases in extreme rainfall linked to global warming

A worldwide review of global rainfall data led by the University of Adelaide has found that the intensity of the most extreme rainfall events is increasing across the globe as temperatures rise.

In the most comprehensive review of changes to extreme rainfall ever undertaken, researchers evaluated the association between extreme rainfall and atmospheric temperatures at more than 8000 weather gauging stations around the world.

Lead author Dr Seth Westra said, "The results are that rainfall extremes are increasing on average globally. They show that there is a 7% increase in extreme rainfall intensity for every degree increase in global atmospheric temperature.

"Assuming an increase in global average temperature by 3 to 5 degrees Celsius by the end of the 21st century, this could mean very substantial increases in rainfall intensity as a result of climate change."

Dr Westra, a Senior Lecturer with the University of Adelaide's School of Civil, Environmental and Mining Engineering and member of the Environment Institute, said trends in rainfall extremes were examined over the period from 1900 to 2009 to determine whether they were becoming more intense or occurring more frequently.

"The results show that rainfall extremes were increasing over this period, and appear to be linked to the increase in global temperature of nearly a degree which also took place over this time.

"If extreme rainfall events continue to intensify, we can expect to see floods occurring more frequently around the world." Dr Westra said.

The strongest increases occurred in the tropical countries, although some level of increase seems to be taking place at the majority of weather gauging stations.

Dr Westra said, "Most of these tropical countries are very poor and thus not well placed to adapt to the increased risk of flooding, which puts them in a larger threat of devastation."
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This work is being published in the Journal of Climate and can be seen online.

The research also involved researchers from the University of New South Wales, Australia and the University of Victoria, Canada.

Source: University of Adelaide Media Release, 1 February 2013


Abstract

Global increasing trends in annual maximum daily precipitation
Seth Westra, Lisa V. Alexander, and Francis W. Zwiers

Journal of Climate 2012 ; e-View
doi: http://dx.doi.org/10.1175/JCLI-D-12-00502.1

This study investigates the presence of trends in annual maximum daily precipitation timeseries obtained from a global dataset of 8326 high quality land-based observing stations with more than 30 years of record over the period from 1900 to 2009. Two complementary statistical techniques were adopted to evaluate the possible non-stationary behaviour of this precipitation data. The first was a Mann-Kendall non-parametric trend test, and was used to evaluate the existence of monotonic trends. The second was a non-stationary generalised extreme value analysis, and was used to determine the strength of association between the precipitation extremes and globally averaged near-surface temperature. The outcomes are that statistically significant increasing trends can be detected at the global scale, with close to two-thirds of stations showing increases. Furthermore, there is a statistically significant association with globally averaged near-surface temperature, with the median intensity of extreme precipitation changing in proportion with changes in global mean temperature at a rate of between 5.9% and 7.7% per degree, depending on the method of analysis. This ratio was robust irrespective of record length or time period considered, and was not strongly biased by the uneven global coverage of precipitation data. Finally, there is a distinct meridional variation, with the greatest sensitivity occurring in the tropics and higher latitudes, and minima around 13°S and 11°N. The greatest uncertainty was near the equator due to the limited number of sufficiently long precipitation records, and there remains an urgent need to improve data collection in this region to better constrain future changes in tropical precipitation.

Source: Journal of Climate Abstract