Climate change increased extreme monsoon rainfall, flooding highly vulnerable communities in Pakistan

Friederike E L Otto, Mariam Zachariah, Fahad Saeed, Ayesha Siddiqi, Shahzad Kamil, Haris Mushtaq, T Arulalan, Krishna Achuta Rao, S T Chaithra, Clair Barnes, Sjoukje Philip, Sarah Kew, Robert Vautard, Gerbrand Koren, Izidine Pinto, Piotr Wolski, Maja Vahlberg, Roop Singh, Julie Arrighi, Maarten van Aalst, Lisa Thalheimer, Emmanuel Raju, Sihan Li, Wenchang Yang, Luke J Harrington, and Ben Clarke.

Environmental Research: Climate, Volume 2, Number 2 (2023), Article number 025001 


This paper examines the role of human-induced climate change in the extreme monsoon rainfall that led to widespread flooding in Pakistan in 2022. The flooding affected over 33 million people, destroyed 1.7 million homes, and caused nearly 1,500 deaths, with disproportionate effects among vulnerable populations.  

The authors use probabilistic event attribution, a scientific method used to determine the likelihood that a specific weather event was caused by human-induced climate change. The authors repeat the analysis using a variety of climate models to assess the robustness of their findings and assess the range of possible outcomes.  

The authors consider two regions in their analysis: (1) the region covering the entire Indus river basin; and (2) a smaller region covering only the southern provinces of Sindh and Balochistan. They define two events as follows: (a) the annual maximum of the mean 60-day precipitation during June–September, over the Indus river basin (capturing the monsoon rainfall season), and (b) the annual maximum of the mean 5 day precipitation in June–September over the Sindh and Balochistan provinces (capturing the most extreme spell). 

The analysis is based on detailed precipitation data drawn from three sources: (1) the Climate Prediction Center (CPC) dataset produced by the National Oceanic and Atmospheric Administration (NOAA) in the United States; (2) the fifth generation of the European Reanalysis (ERA5) dataset produced by the European Centre for Medium-Range Weather Forecasts (ECMWF); and (3) Integrated Multi-satellitE Retrievals for Global Precipitation (IMERG) dataset produced by the Global Precipitation Measurement (GPM) mission. 

Main findings: 

  • Most models show a potentially large increase in likelihood and intensity of 60 day and five-day extreme rainfall values.  
  • Best estimates indicate that climate change has led to an estimated 50 percent increase in five-day maximum rainfall intensity over Sindh and Balochistan provinces 
  • It was not possible to estimate the impact of climate change on 60day rainfall across the basin, due to the high variability in rainfall in the region and relatively short observational datasets, coupled with the possibility that observed changes could have a variety of drivers, including, but not limited to, climate change. 

The authors conclude that intense rainfall has become heavier as Pakistan has warmed, with some models suggesting that climate change could have increase rainfall intensity by 50 percent. The authors note that other factors have contributed to the impact of the floods, including the proximity of human settlements, infrastructure (homes, buildings, bridges), and agricultural land to flood plains, inadequate infrastructure, limited ex-ante risk reduction capacity, an outdated river management system, underlying vulnerabilities driven by high poverty rates and socioeconomic factors (e.g., gender, age, income, and education), and ongoing political and economic instability.