As the climate becomes warmer on average, it makes intuitive sense that we will see more hot days, and we’ve had predictions of this for some time.

However, the duration of heatwaves — how many days in a row exceed a temperature that is unusually hot for a given region — can be very important for impacts on humans, livestock and ecosystems, according to a study from Portland University and published in Nature Geoscience.

Predicting how these durations will change under a long-term warming trend is more challenging because day-to-day temperatures are correlated — tomorrow’s temperatures have a dependence on today’s temperature.

This study takes this effect into account, along with the warming seen in current and historical observations and projected for the future by climate models for a wide range of land regions.

Not only do the heatwave durations increase, but each additional increment of warming causes a larger increase in the typical length of long heat waves.

In other words, if the next decade brings as much large-scale warming as a previous decade, the additional increase in heatwave durations would be even larger than we’ve experienced so far.

Additional consequences

As temperatures rise, of course, the Earth’s ability to evaporate water from land and sea increases exponentially. Tropical areas are likely to experience longer periods of high humidity, and the formation of atmospheric rivers is expected to become more common.

Dangerous flash flooding is also expected to become common. In the last month, shocking flash floods have occurred everywhere from Texas to the northern tip of the South Island of New Zealand.

Already, summers and winters in many areas around the world have become marred by anxiety and disruption. There’s still a good time to be had in hundreds of places, of course, but the idea that bad weather events can now ruin lives and livelihoods on a large scale is sinking in.

The current northern summer has been defined by a tragic surge in deadly flash floods across the United States, underscoring the escalating volatility of our warming world.

Late last week, eastern US states were looking at a significant and sustained temperature increase as a Midwest heatwave moved towards the Atlantic.

Overall, large parts of the US and New Zealand have experienced unusually humid conditions with record amounts of moisture in the air. When cold fronts and other weather systems come along, that moisture gets squeezed but then is wrung out like a water-laden sponge, producing heavy and often highly localised downpours.

In the US, the Trump administration has shifted course and is moving forward with work to develop a new database that will provide Americans with precise estimates of their flash flood risk, enabling them to make more informed home-buying decisions.

In New Zealand, the Government has finally acceded to 10 years of repeated requests for the installation of a $5m rain radar system for the Nelson region, but not until 2027.