Sometimes it seems as if the planet is trying to get our attention: as a state visit to China was ending over the weekend, with superpower leaders “not talking about climate change,” the Financial Times noted that “China was lashed by heavy rains which caused flash floods and evacuations in central and eastern areas…including downpours in Beijing… Jiangmen in the southern Guangdong province received almost a month’s rain on Thursday and Friday.” This followed, though, a period of notable dryness: “Since May, most areas in central and eastern China had less than 20mm of cumulative rainfall and were in various stages of drought from mild to severe,” noted the same FT story. If the planet is going to be so outspoken, what is it trying to tell us?

Overall, higher temperatures mean more water in the atmosphere and more rain falling back to the ground. This is elementary-school science: students in second grade are typically taught the basics of evaporation, condensation, and precipitation. “Pour yourself a glass of water and take a sip. Did you know that the water you’ve just swallowed is the same water that wooly mammoths, King Tutankhamun and the first humans drank? That’s because Earth has been recycling water for over 4 billion years!” So, not news, except that “The amount of water the atmosphere can hold (and eventually release) increases by 7% for every one degree Celsius (1.8 degrees Fahrenheit) increase in air temperature” – and as a result, with the observable warming of the planet (regardless of what’s causing it), “record rainfall extremes have continued to increase worldwide and, on average, 1 in 4 rainfall records in the last decade can be attributed to climate change.”

The message is becoming more clear – and “infrastructure [such as retention ponds and dams] in most parts of the country is no longer performing at the level that it’s supposed to, because of the big changes that we’ve seen in extreme rainfall” (an observation made seven years ago).

A few sentences ago, I quoted a reference to an “average” – and we need to talk about that. People who’ve never taken a statistics class are likely, it seems to me, to think they “know” that if a measure varies over time, its average encapsulates what’s happening. This month, though, a paper in Nature warns that higher average rainfall may not mean a wetter planet, and doesn’t that seem a little weird?

Averages can be tricky: if a tossed coin lands half the time as “heads” and half the time as “tails,” then on average it lands on edge. That average is not a “most likely” outcome, but rather an “almost never.” This is my favorite argument for “any time someone quotes you an average, ask about the distribution” of the values: not everything is a nice symmetric bell curve.

What does this have to do with rainfall? If you’ve ever encountered seriously dry dirt, perhaps after time away from home when you want to rejuvenate a garden, you’ve seen water sit on the surface rather than soaking in. Instead of watering the plants, it just winds up evaporating, perhaps more quickly than expected if the temperature is high. What’s true for your garden is true for the planet, at much larger scale: “The world's rainfall is increasingly packed into bigger storms with longer dry spells in between,” observes USA Today in a simpler-language summary of that paper in Nature linked above. “And a lot of rain all at once causes problems for overwhelmed soil.”

To shift for a moment into that Nature paper’s more academic language, “Intense precipitation can exceed soil infiltration capacity, accumulating at the surface where lower aerodynamic resistance increases evaporation, particularly during longer and sunnier dry periods. The concentration effect—encompassing both radiative and hydrologic partitioning changes—reduces the water retained on land almost as much as total precipitation increases it.”

In an email to USA Today, one of the paper’s authors said in plainer English that “Regardless of how much precipitation falls, when rain and snow come in stronger bursts separated by longer dry spells, less water tends to remain on the land (in soils, lakes, and groundwater) for use by people and nature.” More rain falling, but less water for our faucets. More floods; less food. The averages aren’t what matters.