Jerry Stenger Photo by Nick Strocchia

“Everyone thinks I’m a TV weatherman,” says Jerry Stenger, whose job as director of the Virginia State Climatology Office is less about trying to predict the future and more about looking into the past to solve mysteries about Virginia’s climate. He’s worked with the UVA Medical Center to correlate respiratory problems with changes in weather. He’s testified in court about precise weather conditions on the day of an accident. And he’s the one UVA event planners call each spring to find out their chances of a sunny day for Final Exercises or Reunions weekend.

Researcher Jerry Stenger (Col ‘77) watches the rain clouds and lets Virginians know if a drought is coming. But measuring precipitation levels, explains Stenger, is not simply a task of sticking a ruler in a bucket. The seemingly simple question, “How much did it rain last year?” becomes decidedly more complex after factoring in considerations such as time, place and who’s using the water. “First of all,” explains Stenger, “it’s not just how much rain falls, it’s when.” If you’re trying to fill up your wells and reservoirs, a raindrop in December is worth more than a raindrop in July.

“We had a very dry winter last year, so that’s bad,” Stenger explains. Virginia, which has a recent history of droughts, needs a healthy helping of wintertime rain. In the winter, more rain stays on the ground and makes its way underground. When summer comes, plants awaken and soak up water from the topsoil before it can percolate to groundwater aquifers. Higher temperatures also turbo-charge evaporation.

“Have you ever walked through a cornfield in July?” asks Stenger. “It’s a steam bath.” High levels of evapotranspiration—the sum of evaporation and plant transpiration—results in apocalyptic-sounding “negative rainfall.” Under average Virginia summer conditions, Stenger explains, “you lose about a foot more water than you gain.” Meaning, even in a fairly rainy summer, groundwater levels almost always drop.

Of course, it’s not as if water that goes to plants or back into the atmosphere is truly lost. It’s a matter of perspective. The value of a drop of rain changes based on who you are. While city dwellers could be suffering severe drought conditions, farmers could be doing just fine.

If you’re a farmer of what Stenger calls “row and pasture crops”—plants with shallow roots like hay, soybeans or corn—“you care about the topsoil. The groundwater can be low. Your big concern is: Did it rain last week?” In 2009, for example, many areas of the state were experiencing major water-use restrictions, while well-timed rainfall resulted in yields for some crops that were among the highest ever seen in Virginia.

Conversely, when groundwater levels are abundant—with city dwellers happily washing their cars and playing in their sprinklers—farmers may be unhappy. If Virginia corn farmers, most of whom do not use irrigation, don’t get enough rain during the specific weeks of their “tasseling period”—in which tubules of silk develop—then the kernels won’t develop properly. Even if they were to get a healthy drink of rain afterward, it wouldn’t matter, Stenger says. “They’ll have to just plow in their entire crop.”

Can farmers and city dwellers agree that more rain, whenever it comes, is good? Nope. For farmers, rain’s precise timing, its “tempo,” can make or break their growing season. Five inches over the month of July might be more than welcome, but not if it falls all at once. Hay farmers, although eager for massive summer rainfalls to feed their grasses, have a few days each season when rain becomes their foe. They need dry weather right after the hay has been cut, as it lies drying in the fields. A little sprinkle of rain is all right, but a deluge may cause mold that renders hay toxic for livestock.

A raindrop is never just a raindrop. Its value changes from friend to enemy, moneymaker to toxin. “Plain old rain,” says Stenger, “is a far more complex commodity than one might expect.”