El canvi climàtic i el calent global ocasiona la persistència cada vegada més acusada de fenòmens, meteorològics extrems.
Com que la Terra s’escalfa, tant la velocitat d’evaporació com la precipitació augmenten. I a mesura que la càrrega atmosfèrica d’humitat i la convecció augmenten de manera coordinada amb l’augment de temperatures, també ho fan les màximes intensitats potencials de les tempestes.
Intensifying Equatorial Rains: 3.3 Million Afflicted by Flooding in India and Bangladesh as Hundreds Lose Lives to Landslides from Sierra Leone to Nepal
There’s something wrong with the rain these days. For many regions of the globe, when the rain does fall, it more and more often comes with an abnormally fierce intensity.
This increasing severity of heavy rainfall events is just one aspect of human-forced climate change through fossil fuel burning. For as the Earth warms, both the rate of evaporation and precipitation increases. And as atmospheric moisture loading and convection increase coordinate with rising temperatures, so do the potential peak intensities of the most powerful storms.
(Climate and extreme weather news August 13 through 15)
Sierra Leone — More than 300 Dead, 600 Missing After Deadly Mudslide
This past week, in Sierra Leone — already one of the wettest regions of the globe at this time of year — a very heavy rainfall event generated a severe mudslide that ripped a huge swath of devastation through Freetown. 3,000 people were immediately rendered homeless by the great rush of mud, rock, and soil. But more tragically in excess of 300 people are feared dead with 600 still missing.
This single event represents the deadliest natural disaster on record for Sierra Leone — which also suffered a flood that killed 103 people in 2009. According to news reports, the region in which this disaster occurred has experienced 20 inches more rain than usual over the 30 day period from July 15 through August 15. A total amount of rainfall in a single month period that’s now in the range of 50 inches. Clearly, the surrounding lands could not maintain integrity under the force of such a prolonged deluge. And unfortunately one of the succumbing hillsides let loose into a valley settlement.
(Heavy thunderstorms of Freetown on August 14th. Image source: NASA and Weather Underground.)
A statement by Weather Underground’s Bob Henson provides further climate context for this disaster:
The heaviest downpours in many parts of the globe have become heavier in recent decades, a trend attributed to human-produced climate change and expected to continue. A study led by Christopher Taylor (UK Centre for Ecology and Hydrology), published this spring in the journal Nature, finds that the Sahel’s most intense mesoscale convective systems (organized clusters of thunderstorms) have tripled in frequency since 1982. The recovery of Sahel rainfall since the 1980s only explains a small part of this trend, according to the study authors. They argue that Saharan warming is helping to intensify convection within the MCSs through increased wind shear and changes to the Saharan air layer. “The meridional gradient is projected to strengthen throughout the twenty-first century, suggesting that the Sahel will experience particularly marked increases in extreme rain,” the study concludes.
Pradesh and Nepal Landslides and Floods Kill Over 100 More
Severe rains also on August 14th unleashed a mudslide in Pradesh India that knocked two buses off a cliff — resulting in the tragic loss of 46 lives. The resulting landslide also injured 5 other passengers even as it buried numerous homes along its path.
Across the Bay of Bengal in Nepal flooding and landslides resulted in the loss of 62 lives as 30 districts reported severe conditions. There, rains displaced 1,500 families, destroyed 305 homes, and damaged more than 15,000 other dwellings. Dozens of Nepali roads have been blocked, a school has collapsed, and an airport has been forced to close as severe storms inundated the region.
In India and Bangladesh, 3.3 Million People are Affected by Flooding
In the Indian state of Assam, 84 people have lost their lives due to a massive flood that has now affected 2 million people across 29 districts. 2,734 villages have flooded and 183,584 people have been forced to relocate to one of 700 refugee camps. Meanwhile, across the state, some 3,830 water rescues have occurred. Dozens of roads and bridges have been washed out as rivers rise from moderate to unprecedented flood stages.
(Assam floods on August 14. Image source: Government of India and Floodlist.)
Finally, in Bangladesh, record rainfall has pushed rivers to some of the highest levels ever recorded. The result has been the forced displacement of 368,000 people to 970 temporary shelters as 1.3 million are afflicted by flooding. Tragically, 27 Bangladeshis have also lost their lives due to the extreme flooding. Rainfall rates of up to ten inches per day are contributing to the severe flooding even as water from floods further upstream in India and Nepal are flowing into Bangladesh river systems.
Conditions in Context — Very Severe Equatorial Rains
Overall, these various events may appear to occur separately. However, they are all associated with a very severe Equatorial rain pattern developing from Africa through Southeast Asia and stretching into the Atlantic inter-tropical-convergence zone during 2017. The apparently increased thunderstorm activity is now impacting everything from the intensity of monsoonal rains over Southeast Asia, the severity of storms in the Sahel of Africa, and the early formation of tropical cyclones off Cape Verde during August.
These heavy rainfall features are arguably linked to the climate-change based intensification of the hydrological cycle and, particularly, to the increasing intensity of Equatorial thunderstorms. The overall climate and weather trend for the larger region should thus be noted and these various related events should not be viewed in isolation.