WEATHER NEWS: Pakistan is experiencing a record monsoon season. Here’s why
Record rainfall this summer has pushed Pakistan to its worst flooding in at least a decade. Floodwaters have transformed low-lying areas around the Indus River into swamps. At least 1 million homes have sustained some level of damage, and around 5,500 roads, bridges and shops have been damaged since mid-June. More than 1,160 people have died and 3,500 have been injured from June through August.
Government estimates say that around 33 million people, or 13 percent of the population, have been affected by the floods.
Most of the heavy rain is associated with the summer monsoon pattern over the region. The term “monsoon” describes a seasonal wind shift that brings moist air to South Asia during the summer, resulting in heavy precipitation. The summer monsoon provides 65 to 75 percent of annual water in Pakistan, playing an important role in farming and the livelihoods of residents.
But exceptional rainfall rates have made this season a “monsoon on steroids,” said António Guterres, secretary general of the United Nations.
From June through August, Pakistan has received 190 percent of its normal rainfall. July alone exceeded the total normal monsoon rainfall by about 26 percent, becoming the wettest July on record since 1961. The heavy rainfall saturated soil, preventing the ground from soaking up more water from storms in August. Rainfall during monsoon season peaks in August, which has continued to bring remarkable downpours and flooding.
The most unusually heavy rain fell across the provinces of Baluchistan and Sindh, which have experienced significant widespread damage. Rainfall amounts from mid-June through August were 430 percent of normal in Baluchistan and 460 percent of normalin Sindh. Around 50 different cities have experienced monthly rainfall much higher than normal.
“The season has not ended yet and the total number of rainy days have already almost doubled for several cities,” Bushra Khalid, a research scientist at the Institute of Geographic Sciences and Natural Resources Research, told The Post in an email.
The monsoon system begins as air over higher terrain in Tibet heats up during the summer, creating a wide belt of low pressure known as a thermal low. The thermal low draws in moist air flow from the Arabian Sea and Bay of Bengal.
The monsoon typically takes time to move north into Pakistan in the summer. This year, the Pakistan Meteorological Department said the season settled into the country on June 30, one day earlier than the typical onset.
The summer monsoon enters Pakistan in two different directions, explained Muhammad Fahim Khokhar, a researcher at the National University of Sciences and Technology in Islamabad. First, southwesterly winds from the Bay of Bengal travel along the foothills of the Himalayas and enter Pakistan. The system brings the first monsoon rains to the districts of Sialkot, Jhelum, Islamabad and Lahore, which constitute the northern monsoon belt and is the main region of monsoon activity.
The second pathway comes from southwest winds entering Pakistan from the Arabian Sea, bringing rainfall to the southeastern region of Pakistan. Khokhar said Baluchistan typically remains largely unaffected by the summer monsoon but received major rainfall this year.
“The seasonal low pressure system over the south Asia region is bigger than ever penetrating into the western Pakistan up to Iran and bringing rainfall over Baluchistan province also,” Khalid said. She said the monsoonal trough, which determines the rainfall distribution over Pakistan, is farther south than normal, bringing more rains over southern Pakistan, including Sindh and Punjab.
Researchers also say the exceptional rainfall is caused partly by the presence of La Niña, characterized by cooler surface water in the equatorial Pacific Ocean. The cooler water temperatures pushes the air current known as the Walker Circulation into overdrive across the Pacific Ocean and enhances monsoonal rainfall in South Asia.
2022 is the third consecutive year with a La Niña, which is a rare feat. But Khalid said this year has a “more intense La Niña, bringing intense and devastating monsoon.”
A La Niña was also present during the last catastrophic monsoon season in 2010, which took the lives of more than 2,000 people and is considered the worst season on record. Initial figures suggest this year’s monsoon season could prove to be worse.
Waheed Ullah, an associate professor at the Nanjing University of Information Sciences and Technology, said the flooding could also be tied to the heat waves in Europe.
He said the atmospheric blocking pattern that caused heat waves in Europe also tends to favor above-normal precipitation in Pakistan, bringing in substantial moisture to the area through the Indian Ocean and Bay of Bengal. He and his colleagues have a “firm belief” that a similar moisture transport could have occurred this time as well.
“In past situations like 2003 and 2010, devastating floodings occurred in Pakistan when Europe suffered from heat waves,” Ullah said.
Living in a climate-ravaged world
Researchers say climate change also played a part in this year’s monsoon season.
Temperatures over the monsoon belt in Pakistan have increased at a rate of around 0.18 degrees each year since 2010, Khokhar said. Warmer air can hold more moisture, which can lead to more severe rainfall and subsequent flooding.
Khokhar and his colleagues previously found that the number of rainy days during monsoon season have decreased in recent decades, but said climate change may be increasing rainfall intensity and flash flood risk in Pakistan.
Ullah and his colleagues similarly found that the duration of wet events in the country has decreased, but the number and frequency of extreme events, especially after 2011, has increased.
“The monsoon and the associated extremes over Pakistan in specific and the South Asian monsoon domain, in general, are increasing exponentially,” Ullah said.
Higher-than-average sea surface temperatures over the Indian Ocean have also intensified the season. The warmer sea surface temperatures spurred more evaporation, which made more moisture available for transport over the region and fall as rain. Khokhar said tropical depression systems in the Bay of Bengal and Arabian Sea could have played a significant role along with the increased sea surface temperatures.
The summer rainfall comes after record heat hit Pakistan in the spring, which researchers calculated was 30 times more likely to occur because of climate change. The record heat helped melt glaciers, some of which triggered flash floods in nearby villages. Additional glacier melt throughout the summer has added to the monsoonal flooding.
Pakistan is continually listed as one of the countries most vulnerable to climate change by the Intergovernmental Panel on Climate Change, despite contributing less than 1 percent of recent global greenhouse gas emissions.
Part of the reason is because of its variety of ecosystems, including glaciers, rivers that rely on rains and glacial melt, deserts and mangroves in the south. Khokhar said a large population of Pakistan with poor socioeconomic conditions rely on these natural systems for their livelihoods.
“Pakistan is more vulnerable to slight disturbances in climate because of its delicate ecosystems,” Khokhar said. “It is certain that Pakistan should redesign its developmental plan centered with incorporation of all types of natural disasters, community resilience and sustainability.”