The past century has seen a significant increase in rainfall variability on a global scale due to human-induced warming, with over 75% of the Earth’s land area being affected. This new research, conducted by Chinese researchers in collaboration with the UK Met Office and published in the journal Science, provides systematic observational evidence highlighting the impact of climate change on global rainfall patterns.
The study focuses on the uneven timing and amount of rainfall, showing that dry periods are becoming drier while rainy periods are becoming wetter. The trend of increasing rainfall variability has been particularly pronounced in regions such as Australia, Europe, and eastern North America, raising concerns about the heightened risks of droughts and floods.
The research reveals a systematic increase in rainfall variability since the 1900s, with day-to-day variability increasing by 1.2% per decade globally. This increase in variability means that rain is now more unevenly distributed over time, with the possibility of a year’s worth of rain falling in fewer days or alternating between long dry periods and intense downpours.
Europe, Australia, and eastern North America have been identified as particularly affected regions, with detailed and long-running observations showing a prominent increase in rainfall variability. However, the long-term trend in variability was less evident in other areas, possibly due to random changes or errors in the datasets.
The increase in daily rainfall variability is largely attributed to human-caused greenhouse gas emissions, leading to a hotter and more humid atmosphere that results in more intense rain events and greater swings between dry and wet periods. This poses new challenges for weather and climate predictions, as well as for resilience and adaptation measures by societies and ecosystems.
Factors such as the amount of water vapor present in the air, storm wind strength, and the formation of large raindrops from cloud particles play a significant role in determining the intensity of rainfall. With every degree of global warming leading to a 7% increase in water vapor in the atmosphere, storms are expected to become rainier over time.
Studies focusing on Australia have highlighted the increasing variability in rainfall patterns, with extreme events likely to exceed past expectations. In regions such as Sydney, the maximum hourly rainfall has seen a significant increase over the past two decades, posing challenges for infrastructure preparedness and flash flooding risks.
The growing variability in rainfall patterns not only raises concerns about the risks of droughts and floods but also emphasizes the importance of reducing greenhouse gas emissions to mitigate the impact of global warming. Policymakers need to shift their focus from overall changes in wetness or dryness to the increasing variability that can lead to more devastating climate-related disasters.
As the global climate crisis worsens, it is essential for governments, communities, and individuals to prepare for the challenges posed by rising rainfall variability. By taking immediate action to reduce emissions and limit global warming, we can work towards a more sustainable future and minimize the negative impacts of climate change on our planet.
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