From mid-June to the end of August 2022, Pakistan experienced unprecedented flooding over a large part of the country due to significantly above-normal monsoon rains that far exceeded those of any other year. August alone was the wettest month in the country's history of observation since 1961, with three times the normal amount of rainfall, and especially in the southern provinces of Sindh and Balochistan, rainfall was seven to eight times higher than usual. The Indus River, which runs through the country, reportedly overflowed its banks and submerged thousands of square kilometers of land, affecting 33 million people, resulting in the loss of 17 million homes and 1,500 lives, and damaging many crops.

An analysis of the World Weather Attribution showed that climate change caused by anthropogenic factors is very likely to have increased the intensity of monsoon rainfall.

Among the main findings showed that the flooding was the result of extreme monsoon rainfall in the summer of 2022, combined with several short periods of heavy rainfall in August, particularly in Sindh and Balochistan provinces. Damage was also exacerbated by weak infrastructure.

Such an event could occur once every 100 years under today's climate, but rainfall in the Indus Basin, influenced by various factors correlated with the El Niño Southern Oscillation (ENSO cycle) and other factors, is highly variable from year to year, making it difficult to fully quantify the probability.

To establish the role of anthropogenic climate change in the observed values, a climate model is used to compare trends with and without the influence of anthropogenic greenhouse gases. The area affected by the floods is on the western edge of the monsoon region, and there are significant differences in the nature of rainfall between the dry west and the wet east. Many modern climate models fail to simulate these rainfall characteristics well, and those that barely meet the evaluation criteria seem to tend to predict changes in the frequency and intensity of extreme rainfall events less than the actual observed trends. This discrepancy between observations and model predictions suggests that long-term variations and processes that cannot be supplemented by researchers' assessments play an important role and may not adequately quantify the anthropogenic drivers of climate change, according to the researchers.

Nevertheless, with regard to the five days of extreme rainfall, many of the models and observations analyzed by the researchers indicate that rainfall at strong intensities has increased with warming in Pakistan. Some models suggest that climate change may have increased the intensity of 5-day rainfall by 50%.

In the future, the models suggest that 5-day rainfall intensity could increase under a 2°C warming, while predictions for 60-day monsoon rainfall are highly uncertain.

The researchers believe that their analysis is consistent with the latest IPCC report, which predicts the possibility of increased extreme peak rainfall in Pakistan due to anthropogenic climate change at present and in the future, and recommend that vulnerability to extreme weather events be urgently addressed.

Contributor: IIYAMA Miyuki (Information Program)