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Who will count the rain? In Tampa Bay, it’s this man.

Ever wonder how we know rainfall totals down to the hundredth of an inch? Here's a lesson in the Southwest Florida Water Management District's gauge program.

Florida’s rains are particular. And intense.

Granville Kinsman’s job is to measure them.

“Rainfall,” he said, “drives everything.”

To many of us, the rain just sort of is: an annoyance, a reason to cancel fishing plans, the pitter-patter behind a lazy day or a quenching shower for our flower beds. We give little thought past worried glances toward the green and orange blobs on our weather apps.

Kinsman knows how Tampa Bay’s showers matter down to the decimal point. He leads the hydrologic data section at the Southwest Florida Water Management District, overseeing a small staff that tracks the region’s rain. From north of Homosassa Springs to below Port Charlotte, the agency’s work depends on these records.

Granville Kinsman is the manager of the Southwest Florida Water Management District's hydrologic data section. [ Southwest Florida Water Management District ]

The numbers collected under Kinsman, a geologist, help mark the health of the water system. The data inform how and when the Water Management District restricts water usage during droughts and how it deploys flood control measures. During hurricane season, scientists know the areas that have previously seen the most rain could be even more susceptible to flooding.

The data also serve as a baseline for mathematical models. Tracking dry and wet periods helps staffers make decisions on permits that allow businesses to draw water from nature.

Rain is the linchpin, swelling rivers above flood stage and recharging the aquifer. Downbursts here fall unevenly, complicating the work.

To measure the rain, Kinsman said, the Water Management District relies on 170 gauges, 129 of which return data every hour. They are not the narrow glass cylinders of a garden ornament. Kinsman’s team employs so-called tipping bucket gauges, which look like taupe canisters, roughly the size of a bathroom waste bin. Drops fall into the top, then funnel to a seesaw inside with a bucket on either end.

Exterior and interior views of a tipping-bucket rain gauge, which the Southwest Florida Water Management District uses to gather data on rainfall. [ Southwest Florida Water Management District ]

Kinsman said the device drops and empties a bucket every time it receives one one-hundredth of an inch of water.

“The harder it rains, the harder it is for that mechanism to keep up,” he said. Wind can blow drops sideways, away from the gauge. A data logger records every shift of the seesaw, and a cellular modem reports the figures back to the district.

The wet season, Kinsman said, runs from June to September. About 60 percent of the region’s rain for the year comes in those four months.

The Water Management District’s gauges are spread out, meaning there are gaps in the places where officials gather exact information. To get a broad sweep, Kinsman said, scientists use radar images from the National Weather Service that show intensity of precipitation in shades of color. Data analysts match gauge totals to gradients in the images, Kinsman said, allowing the Water Management District to create a composite rainfall map, with thousands of points instead of a couple hundred.

After one recent Saturday, when downbursts turned the gutters of downtown Tampa into rapids, Kinsman could share with confidence that .44 inches of rain had fallen in Myakka City, 1.73 inches in Trilby, 2.61 inches in Temple Terrace and 3.35 inches at Sawgrass Lake. And he could create a fuller map, color-coded in sherbet strokes of yellow, orange and green, showing the day’s uneven soaking.

A rainfall map for June 6, 2020, produced by the Southwest Florida Water Management District. [ Southwest Florida Water Management District ]

This process of measuring rain has changed since Kinsman started working for the Water Management District three decades ago. Back then, he said, officials still relied on some volunteers to send in recordings from gauges. It was a good way to encourage citizen involvement, he said, but the data were messy.

“A lot of them would go on vacation so we’d end up with these missing periods,” he said. Volunteers checked their gauges at different times, too, whereas now measurements happen on a midnight-to-midnight schedule.

Growing up in Land O’ Lakes, Kinsman was drawn to water. He remembers as a boy using a hose to create artificial streams that picked up loose sand and dirt, depositing the material in larger rain puddles like deltas.

Rainfall records for Tampa Bay date to 1915, but across his personal history he has learned firsthand the rhythms of droughts and global weather patterns like El Niño. He knows when rain comes from the east, and when it comes from the west. During the dry season, he gets a little antsy.

“I like rain,” Kinsman said. “I don’t think I could have enough rain.”

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