To measure drought in the present day, we use data from sensors that constantly record environmental conditions, such as soil moisture, precipitation, and snow water content. But to measure drought thousands of years ago, researchers can use tree rings. Alvin Chang for The Guardian shows how the researchers line up old rings to gather historical data and then do that across a region.
Measuring centuries-old droughts through tree rings
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Percentage of Households in Each Income Level
What percentage of households fall into lower-, middle-, and upper-income levels when you adjust for household size?