Climate change produces wetter and slower tropical cyclones

Hurricanes are moving slower than thus last longer in one place. Harvey's flooding of Texas may be a direct result.

by

    As the Earth's climate warms, the atmospheric circulation changes. In fact, the regular eastward movement of low-pressure systems around the northern hemisphere, as seen in most of the 20th century is now often absent.

    The consequence of an often stationary, or at least slow-moving global weather pattern, which has already been seen in tropical cyclones.

    A study by Jim Kossin, NOAA scientist based in the University of Wisconsin, has shown a general slow-down in the forward motion of hurricanes.

    The measurements show that the forward speed of tropical cyclones has decreased globally by about 10 percent since 1949.

    More importantly, the slow-down at landfall has been 20 percent for Atlantic hurricanes and 30 percent for Asian typhoons.

    Hurricanes and typhoons, and lesser tropical cyclones, generally are carried along with the prevailing breeze; if that wind slows, so do they. To make the double-whammy, a warmer atmosphere carries more water vapour that falls out as more rain, now out of slower-moving cyclones.

    Another study, led by Ethan Gutmann of the NCAR and published in Journal of Climate, re-ran the lifespan of 22 Atlantic hurricanes that happened between 2001 and 2013. The point was to see whether a future climate would re-create these hurricanes with more devastating results.

    Among the group were the well-studied hurricanes Wilma, Rita, Sandy, Isaac, Ike, Ivan, Isabel and Gustav.

    The computer model was run for each storm using the current climate, then for a climate approximately 4.5 degrees Celsius hotter - the amount of warming expected by the end of the century if no attempt is made to control greenhouse gas emissions.

    As a group, the 22 hurricanes in the future simulation had six percent stronger winds, moved at a nine percent slower speed, and had a 24 percent higher rainfall rate. The results are logically consistent and an extension of what is already happening.

    Coastal cities affected by tropical cyclones can expect an increasingly difficult and expensive future. They have flood defences designed and built for the apparent steady-state conditions of the 20th century.

    This century offers higher sea levels, heavier rain, and more rain, from slower-moving hurricanes.

    SOURCE: Al Jazeera


    YOU MIGHT ALSO LIKE

    'We scoured for days without sleeping, just clothes on our backs'

    'We scoured for days without sleeping, just clothes on our backs'

    The Philippines’ Typhoon Haiyan was the strongest storm ever to make landfall. Five years on, we revisit this story.

    How Moscow lost Riyadh in 1938

    How Moscow lost Riyadh in 1938

    Russian-Saudi relations could be very different today, if Stalin hadn't killed the Soviet ambassador to Saudi Arabia.

    Daughters of al-Shabab

    Daughters of al-Shabab

    What draws Kenyan women to join al-Shabab and what challenges are they facing when they return to their communities?