Droughts are lasting longer and rainfall is becoming more erratic across the Western hemisphere, according to a new study published by the US Department of Agriculture.
Against the backdrop of steadily warming temperatures, the researchers found that total yearly rainfall has decreased by an average of 0.4 inches over the last half-century, with the longest dry period in each year now lasting up to 32 days.
The researchers also found that extreme droughts are occurring more frequently in the majority of the West, historical weather data has shown that there is a year-to-year variation of both total rainfall amounts and the duration of dry periods.
The rate of increasing variability of rainfall within each year also appears to be accelerating, with greater portions of the West showing longer drought intervals since 2000 compared to previous years.
Joel Biederman, senior author of the study said: ‘The greatest changes in drought length have taken place in the desert Southwest. The average dry period between storms in the 1970s was about 30 days; now that has grown to 45 days.
‘Consistency of rainfall, or the lack of it, is often more important than the total amount of rain when it comes to forage continuing to grow for livestock and wildlife, for dryland farmers to produce crops, and for the mitigation of wildfire risks.’
Co-senior author William K. Smith, assistant professor at the University of Arizona, added: ‘We were surprised to find widespread changes in precipitation have already occurred across large regions of the West.
‘For regions such as the desert Southwest, where changes clearly indicate a trend towards longer, more erratic droughts, research is urgently needed to help mitigate detrimental impacts on ecosystem carbon uptake, forage availability, wildfire activity, and water availability for people.’
In related news, summers in the Northern Hemisphere may last nearly half of the year by 2100, according to a new study published in the journal Geophysical Research Letters.
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