The monumental scale of the devastation and human suffering wrought by the August floods now ravaging large parts of Pakistan is difficult to fathom. But perhaps the most heart-wrenching aspect of the floods is that they aren’t entirely unprecedented. In fact, one of the most widespread flood disasters in modern global history gripped Pakistan just 12 years ago.

By some measures, the 2010 floods may have been even worse than the 2022 event, though we won’t know for sure until the current floods have run their course. Here is a comparison of the statistics to date; the 2022 estimates from various sources could rise substantially.

People affected:  20 million in 2010; 33 million in 2022;

People displaced:  6 million in 2010; 3.1 million in 2022;

Fatalities:  1,985 in 2010; 1,136 in 2022;

Homes destroyed:  1.8 million in 2010; 300,000 in 2022;

Livestock killed:  200,000 in 2010; 700,000+ in 2022;

Damage (2022 USD):  $12.9 billion in 2010; $10+ billion in 2022

One clear player in both the 2010 and 2022 disasters is La Niña. Both years featured La Niña conditions during northern summer. In fact, for the months of May through July, the two strongest La Niña years of the 21st century happen to be 2010 and 2022.

There’s clearly more than La Niña at work, though, given the severity of the Pakistan flood impacts in these two years versus major flood events of decades past.

The 2010 event occurred just before the widespread use of attribution research, the line of study that uses climate models to discern how much of a role climate change played in a particular weather calamity. What we do know from analyses of the 2010 event is that there’s no single route by which a warming planet is affecting Pakistani flood disasters. There are three distinct types of destructive flooding involved, each one influenced in a different way by the changing climate. Here are the three, ranked from least important to most important.

Glacial outburst floods. It’s widely accepted that there is more glacial ice in Pakistan than in any other nation outside the polar regions (although border disputes add some uncertainty to the tallies).

Long-term warming has led to increasing numbers of glacial lake outburst floods (GLOFs), whereby a meltwater-engorged lake bursts through its boundaries and floods areas downstream. In the Pakistan-administered Gilgit-Baltistan, part of the Kashmir region, there are roughly 3000 glacial lakes.

La Niña tends to intensify the springtime heat that precedes the summer monsoon across Pakistan and India. This year’s pre-monsoonal heat was especially fierce, as Jeff Masters discussed in a May 5 post. In southeast Pakistan, the city of Nawabshah hit 49.5 degrees Celsius (120.2°F) on May 1.

For various reasons, the springtime heat wave appears to have been notably less deadly in India and Pakistan than was initially feared. However, the extreme heat may well have contributed to several high-profile GLOFs, including one in the Hunza Valley on May 7 that brought down a major bridge and damaged two power plants, and another in the Laspur Valley on July 3 that cut off roads and stranded spectators from a large festival.

Sher Muhammad, a glaciologist at the Nepal-based International Centre for Integrated Mountain Development, told GlacierHub that temperatures near the Hunza Valley in April were closer to the average expected in May.

While the GLOFs are major concerns in their own right, they are not typically the biggest factor in the kind of nationwide flood disasters seen in the summers of 2010 and 2022. While rainfall was around 50 millimeters (2 inches) above average across most of northern Pakistan in August, temperatures were below average, according to Muhammad.

“The floods in 2010 and this year are primarily monsoon-driven, with some role [from] glacier melt,” said Muhammad in an email.

Pre-monsoonal thunderstorms. The intense heat of June and July, just before the arrival of the monsoon, can kick off strong thunderstorms that can spawn localized torrents and flash floods over the rugged, mountainous landscape of northern Pakistan. Rainfall from these storms is not typically as widespread as the monsoonal rains that normally peak in August.

Several intense pre-monsoonal bursts of thunderstorms affected northern Pakistan in July 2010, according to analysis by Simon Wang of Utah State University. Although average July rainfall across northern Pakistan did not increase from 1970 to 2010, Wang found a distinct increase in intense rainfall events – a hallmark example of our warming planet’s well-established tendency to pack rains into briefer, more intense bursts. Wang outlined the trends for Pakistan in a 2011 paper for the Journal of Geophysical Research.

In contrast to the typical pre-monsoonal storms, July 2022 brought an unusually early arrival of a signature monsoon pattern, which pushed heavy rain into southern Pakistan. “The monsoonal westerly wind near Pakistan became southwesterly, channeling more moisture,” said Wang in an email. “It was also cooler and more rainy in the coastal area of Pakistan.

“All these set the stage [for] saturated soil that could not take any more water from the August storms.”

Monsoon rains. By August, the clouds, moisture, and rain of the full-fledged summer monsoon have typically pushed from India across much of Pakistan. Sitting on a climatological transition zone between arid and moist climates, Pakistan can experience widely varying monsoon rainfall totals from year to year.

Wang found no long-term trend from 1970 to 2010 in rainfall amounts or intensities across northern Pakistan. However, another study found a peculiar aspect of the rains in 2010. A group led by Robert Houze of the University of Washington analyzed the 2010 event in the Bulletin of the American Meteorological Society.

During the last week of July 2010, a strong tropical depression from the Bay of Bengal moved all the way across northern India, eventually pushing a slug of extremely moist air against the higher terrain of central and northern Pakistan. According to Houze and colleagues, the rains included not only strong thunderstorms but widespread steady, stratiform rain, the type one might see bridging cells across a large storm complex in the U.S. Midwest.

The authors noted that “… such large areas of stratiform rain are almost never seen in this arid mountainous region.”

Much as in 2010, the 2022 flood disaster in Pakistan was also heavily influenced by a tropical cyclone. Tropical depression BOB 07 (which refers to the seventh Bay of Bengal storm of the year) moved across northern India over the third week of August, maintaining its intensity across a waterlogged landscape soaked by BOB 06 just a few days earlier.

The remnants of BOB 07 then moved into the southern Pakistan provinces of Sindh and Balochistan. Making matters worse, the remnants stalled and interacted with a semi-stationary low in upper levels of the atmosphere northwest of Pakistan. The setup is akin to tropical-midlatitude dynamics that came into play during Hurricane Harvey’s rains in 2017 and the disastrous floods of Louisiana in 2016, according to Wang.

August has produced record rainfall over Sindh and Baluchistan, including around 500 millimeters (19.69 inches) averaged across Sindh – an area the size of North Carolina.

One town in Sindh, Padidan, reported a phenomenal 1187 millimeters (46.74 inches) for the period August 1-26, according to Floodlist. The total was almost four times Padidan’s previous record for the entire month.

There’s some evidence that tropical cyclones in the Bay of Bengal may shift northward and weaken as climate change proceeds. If so, that could potentially open the door for an increase in westward-moving depressions that traverse northern India and sweep into Pakistan.

Globally, warming oceans are supplying tropical cyclones with more water vapor, allowing for intensified rainfall. A 2021 paper in Nature Communications by Oscar Guzman and Haiyan Jiang, of Florida International University, found that the average rainfall produced by a tropical cyclone increased by 1.3% per year from 1998 to 2016, which the authors attributed to rising sea surface temperature and enhanced atmospheric moisture. The trend was similar across the spectrum of tropical cyclone strength.

A growing nation faces a growing problem

Pakistan’s contribution to the planet’s burden of greenhouse gases is minuscule (less than 1% of recent global emissions), but it will bear some of the worst effects of climate change of any nation. The Global Climate Risk Index for 2021 – calculated by the nonprofit Germanwatch based on data from Munich Re – ranked Pakistan as the eighth most vulnerable country on Earth to long-term climate risk.

From 2000 to 2019, the nation had an average of 502 climate-related deaths per year and average losses per year of $3.8 billion USD, representing about 0.5% of Pakistan’s gross domestic product.

Rapid growth is increasing Pakistan’s vulnerability to natural disasters. Pakistan now ranks as the world’s fifth most populous nation, with an estimated 230 million residents as of 2022. In the 12 years since its 2010 flood disaster, Pakistan has added more than 50 million people – an amount larger than the entire population of more than 100 other countries.

Pakistan’s two megacities, Karachi and Lahore, are growing quickly, but close to two-thirds of all Pakistanis live in rural areas, including the flood-prone river valleys that slice across the rugged landscape of central and northern Pakistan.

In the BBC interview above, Sherry Rehman, Pakistan’s federal minister for climate change, acknowledged the challenges ahead: “We’re a very small greenhouse gas emitter … so I don’t think it’s our mitigation efforts that have been lacking. Yes, certainly, we have to build back climate-resilient infrastructure and we have to focus on adaptation. We’ve been very focused on our global promises on mitigation, but that’s led us nowhere, as you can see.”

Ways you can help:

Pakistan Red Crescent Society (part of the international Committee of the Red Cross)

Medicins Sans Frontiers/Doctors Without Borders

UNHCR (United Nations High Commissioner for Refugees)

Jeff Masters contributed to this post. Website visitors can comment on “Eye on the Storm” posts (see comments policy below). Sign up to receive notices of new postings here.