Is it too early to be optimistic about this year’s Rio Grande flow? – jfleck at inkstain

Yes.

But that doesn’t stop me!

The Jan. 1 forecasts, courtesy of Angus Goodbody of the NRCS, are for flows in Otowi (end of the Rio Grande Valley of Central New Mexico) and San Marcial (the tail) for “normal” flows, where “normal” is defined now by the median of the flow from 1991-2020.

Courtesy of NRCS

The reason that it is definitely too early to be optimistic that it’s only January! The remaining months of the winter snow accumulation season will be either wet, or dry, which will make all the difference. As Anne Marken, Middle Rio Grande Conservation Area Water Operations Division Manager, explained to the district board at the meeting yesterday afternoon, “There is a lot of winter left”.

There are a couple of good signs, though.

First, soil moisture in the headwaters region is significantly better than the previous two years, when dry soil and shallow aquifers took a major snowfall before reaching the rivers. This is partly due to the better monsoon season of 2021. (Click image for link to NRCS cool (new?) Data map).

Secondly, it has actually snowed. The snow pack is not great, and is concentrated along the western edge of the upper reaches of the basin, but it is a pretty good start.

But see Marken’s comment “a lot of winter left”.

Note on the data:

For “normals” for this type of analysis, the water / forecast / climate management community uses the mean and / or median over a 30-year period. This changes every ten years, and for 2022 we now need to get used to the 1991-2020 time window, moved for this year’s forecast from the 1981-2010 window we’ve been putting use.

By dropping the relatively wet 1980s in favor of the relatively drier teens, we have a “normal” drier in comparison.

NRCS is also shifting its normal forecasts, the numbers Goodbody publishes each month, from using the mean for the reported “normal” to the median. Statistics nerds will understand that the median better reflects the central trend for skewed datasets like runoff, but I am not one of those people so think about the difference and apply it to my water instincts run off makes my head hurt. Thankfully, NRCS’s Goodbody (I think of it as our “concierge data forecast”) shared a great new tool for comparing the two time periods and two different measures of central tendency.

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