Doubts About Droughts

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From Watts Up With That?

Commentary by Kip Hansen — 17 August 2023

Let’s talk about droughts.  Unfortunately, to do that, we’d have to understand what droughts are.  And that understanding doesn’t come easy.

“Drought is a complex phenomenon which is difficult to monitor and define. Depending on the variables used to characterize it and the systems or sectors being impacted, drought may be classified in different types such as meteorological (precipitation deficits), agricultural (e.g. crop yield reductions or crop failure, related to soil moisture deficits), ecological (related to plant water stress that causes e.g. tree mortality) or hydrological droughts (e.g. water shortage in streams or storages such as reservoirs, lakes, lagoons and groundwater).” Alimonti (2022) (currently threatened with retraction due to unscientific pressure from the Climate Crisis Gang)

Or, according to the National Geographic:  “Drought is a complicated phenomenon, and can be hard to define. One difficulty is that drought means different things in different regions. A drought is defined depending on the average amount of precipitation that an area is accustomed to receiving.”… “A drought in Atlanta could be a very wet period in Phoenix, Arizona!”   (National Geographic isn’t threatened with retraction…though many of its entertainment articles – masquerading as ‘science’ —  should be. NatGeo is owned by the entertainment arm of Disney Corporation.)

There are at least 11 types of droughts mentioned at

The end result of this situation is that there is no single metric capable of determining or representing the presence or absence of drought.  Thus, measuring or quantifying something as vague as “number of droughts globally” or “percentage of the world under drought” becomes almost impossible.

Just to give a taste of the sources of possible confusion about droughts, the WestWide Drought Tracker  currently offers the following drought  images for the western Unites States, all for July 2023:

The maps all seem to agree that it has been or is droughty in the Northwest (Washington, Oregon, Northern Idaho) but there is little agreement elsewhere.

So, when we want to write about “The Drought” in California?  Which of these should we use? Which of these did your local newspaper or weather broadcaster use?  How and why did he chose that particular one?

It is possible to dig in and find out what each different image is telling us but it is not easy.

What about the U.S. Drought Monitor?  They offer this view:

And this:

The two maps are pretty similar, the upper one has the state boundaries and the lower has areas by Drought Intensity and Drought Impacts.

However, it is difficult to find even one of the WestWide Drought Tracker views that look like either of the U.S. Drought Monitor views.  Yet they are for the same period (WestWide charts are only a week later than the end of July). How can this be?

Isn’t drought obvious?

The U.S. Drought Monitor [USDM] site tells us this:

“How do we know when we’re in a drought?

“When you think about drought, you probably think about water—or the lack of it. Precipitation plays a major role in the creation of the Drought Monitor, but the map’s authors consider many data sources. Some of the numeric inputs include precipitation, streamflow, reservoir levels, temperature and evaporative demand, soil moisture and vegetation health. No single piece of evidence tells the full story, and neither do strictly physical indicators. That’s why the USDM isn’t a statistical model; it’s a blend of these physical indicators with drought impacts, field observations and local insight from a network of more than 450 experts. Using many different types of data and reconciling them with expert interpretation is what makes the USDM unique. We call it a convergence of evidence approach.”

Let’s be clear:  There are some numerical inputs (things that have been measured).  There are many subjective inputs:  vegetative health, field observations, local insight.  Apparently, there are some indicators that are not “strictly physical” that are considered.  (What these could possibly be, regarding drought, is a mystery to me…maybe emotional indicators?)   All that is then subjected to “expert interpretation” producing “a convergence of evidence”.  I don’t mean this as a criticism – I’m simply telling you what the USDM says their maps represent.  Maybe this is in response to the problems and confusion caused by the 12 images using differing indices changing over time periods from WestWide?  Is it better to have one-drought-image-to-rule-them-all?  I don’t know.

And what is the WestWide Drought Tracker?  It is brought to us by the University of Idaho, the Western Regional Climate Center, and the Desert Research Institute.  They offer many standardized drought indices, each of which is explained on their Overview page.   Their site offers:

What products are available on WWDT? (via this page)

Drought Indices (links below are to additional explainers for each)

   Palmer Drought Severity Index (PDSI)

     Self-Calibrated Palmer Drought Severity Index (sc-PDSI)

        Palmer Z-Index

  Standardized Precipitation Index (SPI)

    Standardized Precipitation Evapotranspiration Index (SPEI)

Climate Data (via this page)

Temperature Data and Anomaly (from 1981-2010 normals)

Temperature Percentiles

Precipitation Data and Anomaly (from 1981-2010 normals)

Precipitation Percentiles

All these are involved with the idea of drought.  All of them have caveats, for instance: They note that for the Palmer Indices, particularly PDSI,  “Snow and its effects are not represented.”   NCAR says the PDSI “Does not account for snow or ice (delayed runoff); assumes precipitation is immediately available”.  We must remember, they are indicies, each one is an index.  All of the indices are calculations, various models, with multiple inputs, many of which are not measurements but parameters.

“What is index in a research project?  An index is a composite measure of variables, or a way of measuring a construct….using more than one data item. An index is an accumulation of scores from a variety of individual items.”  [source] Or “An index is a type of measure that contains several indicators and is used to summarize some more general concept.” [source]

In other words, an index is a numerical scaling created by combining various factors believed to be integral to the concept – in this case: drought.

NCAR claims that “Maps of the monthly self-calibrating Palmer drought severity index (SCPDSI) have been calculated for the period 1901–2002 for the contiguous United States (20°–50°N and 130°–60°W) and Europe (35°–70°N, 10°W–60°E) with a spatial resolution of 0.5° × 0.5°”.  The procedure for calculating the SCPDSI (sometimes sc-PDSI) for any location is given in this paper (see section 2, second paragraph).  Count the number of assumed values, parameters, non-measured factors.    Raise your hand if you think that climatic records accurate enough for this procedure have been carefully and continuously kept at a spatial resolution of 5° for the entire United States since 1901.   How about for the entire world

In the present day, we are being told “Human-induced climate change has contributed to increases in agricultural and ecological droughts in some regions due to evapotranspiration increases (medium confidence).”  IPCC AR6 Chapter 11

With our present confusion in measuring of drought and droughts, it is no surprise that the IPCC has only medium confidence in the above statement and limits its cause to evapotranspiration increases and to  some regions. (Is medium confidence a “maybe”, a “might be” or a “probably”?)

So, I have my doubts about droughts.  I have doubts that we can accurately ‘measure’ them on any scale other than locally.  We can tell when an entire region is in a desperate drought – like the Horn of Africa has currently causing famine or the Southwest U.S. which has been experiencing various levels of drought on a long-term scale but even there, in the desert, some of our indices (SPIs) show a lack of drought. For example,  in Arizona.  

But there is no line solidly enough drawn – no strict definition — no single dependable scientific metric — that we can use to allow us to determine if there are more or fewer droughts or wider areas of drought ­– the definitions and even the indices are far too ambiguous for use in any real scientific manner.  Mapping and analyzing various indices cannot tell us very much about the world. We can say this or that  index is trending up or down but the indices are not real world conditions, the indices are not droughts — they can tell us something, but cannot answer a question such as:  Are there more droughts globally now than in the past?  

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Author’s Comment:

The same issue affects a lot climate research and data sets.  We see graphs and charts of things that are not “real”, not physical — they are like the drought indices, blends of some measurements, some maths, some statistics and some expert interpretations.   I am sorry but these are not truly proper fodder for scientific study.  Strict science requires actually measuring the thing of interest…not something “sort of like it”. 

And we see vast, huge,  enormous amounts of time spent analyzing these data sets, many of which cannot possibly be accurate representations of what they are claimed to be.  This is as simple as a single weather station’s Daily Average Temperature – it is not the average of the day’s temperature readings at all but the median of the instantaneous high and low.  This erroneous data is blended into regional and/or national data bases which then are further averaged, krigged, etc. into even more synthetic data which is also not what it claims to be.  On and on….

The moral of the story: keep your eyes open and make sure you ask exactly what has been measuredif it was measured at all, and make sure that you know the implications of the answers those questions.

Thanks for reading.