Why drought relief takes time: parts of WNY still in moderate drought

Weather Blog

Featured image courtesy of USGS

ROCHESTER, NY (WROC) – Parts of Western New York are still in a moderate drought for the 3rd week in a row according to the U.S. Drought Monitor (USDM).

The beginning of our spring has been nothing short of dry, but we finally got some much needed rainfall that helped dial back our rain deficit, more so for the month of April than than for the season itself. You may think that our recent rain would be enough to relieve us from our ongoing dry conditions across the region, but there’s more to assessing drought in an area than just rainfall.

I reached out to Richard Heim from the National Centers for Environmental Information to see what really goes into assessing drought for a given area, and for a more in depth look at WNY specifically. To sum things up, even though it rained quite a bit last week, it just wasn’t enough to overcome the drought conditions in place. The rain did contribute to preventing any further deterioration into higher levels of drought, but it takes more than just a few bursts of rain to overcome the dry that’s been building up for so long.

Think of this: Similar to how medicine is used to cure sickness, it takes several consistent doses of the same medicine to fully “cure” or get rid of the sickness. While a few doses may provide some relief to the symptoms, it may not be enough to fully cure it altogether.

The precipitation that we received this past week was considered above normal for the week, but wasn’t enough to make up for the deficit over the past several months.

Heim says when assessing drought, “we need to assess all time scales,” along with the fact there are multiple factors that go into deciding how dry an area actually is.

Local climate, soil moisture, daily and average precipitation, and streamflow are just some of the main variables that contribute to the balancing act between such highly variable factors.

The Standardized Precipitation Index converts precipitation into a value that’s directly related to the USDM, which means it’s this index that is heavily weighted in the final value. Essentially, an SPI that’s continuously a value of -1 indicates a drought event. The event is considered to be ongoing until the SPI reaches a value of 0. However, there isn’t a specific standard in place, meaning an SPI of -1 or less can be considered drought to some, while others consider anything less than 0 a drought.

There are other ranges used in the USDM classification scheme such as Palmer Drought Severity Index (PDSI), CPC Soil Moisture Model Percentiles, and USGS Weekly Streamflow Percentiles.

Heim states, “using the “convergence of evidence” approach, we need to integrate all of these indicators (and more not shown) into the Dx category that they are “converging” to.  When the data for next week become available, the assessment will be made for the 4/27 USDM.”

Accumulated Precipitation for Rochester

The last stretch where Rochester had a surplus of rain from the beginning of meteorological spring up to now was back in 2018.

This year our spring so far has been spent well below average levels for rainfall. You can also spot where we received our “bursts” of rainfall. Even with the rain, deficits for the spring season are still very much present.

Most of our rain came towards the second half of our spring stretch so far with creeks and streams now flowing at a decent pace, which may be an indication our drought relief is on the way soon.

According to the U.S. Geological Survey (USGS), “The beginning of a drought is difficult to determine. Several weeks, months, or even years might pass before people know that a drought is occurring. The end of a drought can occur as gradually as it began. Even when a drought has been broken it may not be truly over.”

Will there be more rain in the forecast? Click HERE for the latest updates from the News 8 Weather Team.

~Meteorologist Christine Gregory

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