A late spring, early summer, when-will-it-end drought is currently making our lives miserable in many parts of Virginia.
In my county we’ve ticked up to ‘severe drought’ status. This is better than ‘extreme,’ and not as good as ‘moderate;’ but most of us are just referring to it as the summer we decided to give up on our hopes and dreams and pray for the onset of winter.
And as it’s the election year – possibly The Sweet Meteor O’ Death too.
High temperatures in the region for weeks have also contributed to a general pissed-offedness. If you have friends or relatives who work outside professionally, it may be best to avoid them until you see the first Pumpkin Latte in your Instagram feed.
Don’t forget to add relative humidity my California friends…
Just in case you need that in Celsius…
Curious to see if what I was feeling matched what was actually happening, I got up close and personal this week with the U.S. Drought Portal — a website managed by NOAA’s National Integrated Drought Information System (NIDIS) – to get some stats on this drought and our historical episodes of drought. A fascinating dive – no pun intended.
As they say on the site (and as I can confirm as a native Californian relocated to Virginia) “Drought in Maine looks very different than drought in New Mexico.”
Making Sense of Terms
Drought is more complicated than ‘Has it rained, and how much?’ That’s meteorological drought, and the number we instinctively look up while surveying our crispy hostas, but a better definition of drought is the imbalance between water supply (precipitation) and water demand (evapotranspiration). On a very basic level, as temperatures increase, so does demand. We’re living that in Virginia right now.
You know it’s bad when the Geranium macrorrhizum is browning
In terms of meteorological drought and rainfall, the words ‘normal’ and ‘abnormal’ are also difficult terms to wrestle with as a layperson. The latter is not only a matter of scientific fact (how many hundredths of an inch we are deviating from mean precipitation, i.e. ‘normal’), but an instant pejorative.
‘Abnormal’ feels frightening and foreboding, even if we realize somewhere in the back of our minds that we are dealing with precipitation averages — and averages need ranges to be calculated in the first place.
The Standard Precipitation Index (SPI) was developed in the early nineties to more accurately quantify that number for various regions over specific time periods using data going back to 1895. This gives us rankings such as “driest (or wettest) on record” or the words “record breaking” — which are eagerly pounced upon by news platforms looking for stories to keep us up at night, but it is not without its weaknesses as it is a indexed measurement of precipitation only.
Some plants are hanging tough – In terracotta no less! Carex x ‘Feather Falls’
Swimming Through Statistics
You can break a record by one one-hundredths of an inch that stretches back to records set 100 years ago – or merely 5. Which is not to downplay how valuable these data are, but to help us accurately and calmly navigate them.
For instance, June was our driest June in Virginia since precipitation was first recorded in 1895. Conversely, May only ranked 105th driest in the same 129 years. The driest May happened in 1911. The driest April in 1942. And in the period between January and our driest June ever, the state of Virginia is actually up in measurable rainfall by seven tenths of an inch.
That doesn’t make us feel better about our hostas of course, because it’s also not the whole story.
As fascinating as this chart is, it only shows one aspect of drought – historical precipitation.
What these data can’t show you is all the other variables such as “rainfall, streamflow, groundwater levels, regional climate, soil moisture, water storage in reservoirs, ecological conditions, municipal water restrictions, and the time of year” (according to NIDIS). These are evaluated on a weekly basis to come up with the US Drought Monitor Map.
That’s an incredibly handy tool to more accurately assess what we’re dealing with, but sadly, that number crunching only goes back 24 years to 2000.
And More Statistics….
There are thoughts that a newer (2010) Standard Precipitation Index – the SPEI — might be able to model evapotranspiration from 120 years of historical data (since 1900), and successfully pair them with precipitation data to come up with a more complete picture.
I’m interested to know why it hasn’t been adopted by NIDIS yet. Perhaps (and this is most likely a gross over generalization), there are just too many values within the datasets to provide an accurate picture? We’re talking about averages of sun hours, wind speed, cloud cover, temperature, relative humidity, solar radiation, etc. – all plugged into a function and tied to another function.
And my guess is, that such a feat is one thing when, in the year 2000, scientists get together and begin to gather the same data in the same way across agreed upon geographical points (hence the Drought Monitor Map); but very different when we have to go back and dodge gaps in historical data.
I don’t know, but I do know that the math is definitely beyond my college statistics class.
Patterns of Drought Encourage Adaptable Plants – And Gardeners
Beyond statistics (which you can very quickly find yourself clicking through for hours) I very much appreciate the neutral but specific language that much of this site employs.
“Drought is a normal climate pattern that has occurred in varying degrees of length, severity, and size throughout history.” says the NIDIS, and boy they’re not kidding. Examining the handily graphed SPI data for Virginia going back to 1895, it looks as if our major issues of precipitation often have more to do with too much rain than too little.
Regardless, it was a very good dive, and I heartily recommend you have a look for your state. You can view 24 years of the Drought Monitor Map, or 129 of the SPI. Or you can even look at Paleoclimate data reconstructed from tree ring studies.
I did not come away feeling happy about the current drought, but more capable of putting it into historical perspective. That energizes me to be adaptable and plant for new patterns, rather than give up the ghost and shake my fist at the sky.
I’ll save that for the election. – MW
A Deeper Dive Into Drought originally appeared on GardenRant on July 18, 2024.
The post A Deeper Dive Into Drought appeared first on GardenRant.
