Local weather watchers have been dutifully documenting San Antonio’s temperature, precipitation, and other climate data for 140 years. If you’re curious how this year’s drought compares to past dry spells, meteorologist Robert Blaha with the National Weather Service has done you a huge favor.

Blaha helped dig up old climate records and published monthly rainfall totals for San Antonio going back to 1871. I stumbled across this interesting piece of the city’s weather history while helping out with a story about the drought, and I made this interactive chart based on the data. (There are a few gaps in the rainfall totals in the 1800s, so the chart starts at a nice round number — the year 1900.)

“We were able to find the records,” Blaha told me. “In the 1800s, they hand wrote (the climate data) in ink. It was in a paperback book. When I came here in 1975, they were in notebook format. In 2050, they’ll be in the format of that day.”

Blaha said the rainfall gauge in San Antonio has changed locations over the years. In the early days it was at a co-op station and then moved to Fort Sam Houston. In 1891 it moved to a downtown office building. Somewhere along the line it was at Stinson Field. In the 1940s it moved to the San Antonio International Airport and stayed there ever since.

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All that work helps us compare this year’s drought to past dry spells. This year, we’ve received 5.6 inches of rain so far in San Antonio. That’s about half the total precipitation for the lowest year on record since 1900, when it rained 10 inches in 1917.

In 2010 it looks like we got quite a bit of rain –37.4 inches. But click on the monthly figures for 2010 and 2011. The data show that September 2010 was our last significant taste of rain.

In the nine months since then, we’ve barely gotten anything.

(Photo credit: Terry Shuck on Flickr)