Drought Factcheck

By Paul Homewood

 

One of the frequent claims about global warming is that it will lead to more severe droughts. For instance, the WMO were crystal clear in their latest Greenhouse Gas Bulletin:

The last five years have been the hottest ever recorded. The consequences are already making themselves felt in the form of more extreme weather events and associated disasters, from hurricanes to drought to floods to wildfires.

The Heartland Institute’s factcheck addresses this, with a particular focus on the US, for natural reasons as they are a US outfit.

 

Bullet-Point Summary:

• The United States is benefiting from fewer and less extreme drought events as the climate modestly warms.
• In 2017 and 2019, the United States registered its smallest percentage of land area experiencing drought in recorded history.
• The United States is undergoing its longest period in recorded history with fewer than 40 percent of the country experiencing “very dry” conditions.
• The U.N. IPCC reports with “high confidence” that precipitation has increased over mid-latitude land areas of the Northern Hemisphere (including the United States) during the past 70 years, while IPCC has “low confidence” about any negative trends globally. (See https://www.ipcc.ch/site/assets/uploads/sites/2/2019/06/SR15_Chapter3_Low_Res.pdf, p. 191.)

Short Summary: Real-world data show drought in the United States has become less frequent and severe as the climate has modestly warmed. Moreover, the United Nations reports “low confidence” about any negative trends globally. Droughts have always occurred, and they always will, so alarmists cannot claim that any droughts are necessarily caused by global warming. Instead, analysis of global and U.S. drought data show the droughts that have occurred recently are less frequent and severe than the droughts of the past several decades.

For example, the National Oceanic and Atmospheric Administration chart below shows that the United States is undergoing its longest period in recorded history without at least 40 percent of the country experiencing “very dry” conditions. Note also the peaks in drought around 1978, 1954, 1930, and 1900 are much larger than what the U.S. experienced in the 21^st century and the late 20^th century.

Figure 1: U.S. Wet and Dry Extremes

Figure 1: Percentage of United States experiencing “very wet” (in green) and “very dry” (in yellow) conditions. Source: National Oceanic and Atmospheric
Administration: https://www.ncdc.noaa.gov/temp-and-precip/uspa/wet-dry/0.

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https://climateataglance.com/climate-at-a-glance-drought/

 

Picking up on the IPCC link, SR15 also stated:

 

 

Regional variations can of course occur for all sorts of reasons, particularly multidecadal ocean cycles. Overall though it is abundantly clear that the WMO’s claim has no scientific basis whatsoever.

 

The case of the US is particularly interesting though. Just look again at the NOAA chart:

Taking national rainfall trends can be misleading, as they may cover up regional variations. However this tool measures the area of the country experiencing either extreme wet or extreme dry conditions. NOAA define “extreme” as:

Climate divisions with a standardized anomaly in the top ten percent (> 90th percentile) of their historical distribution are considered "very warm/wet" and those in the bottom ten percent (< 10th percentile) are classified as "very cold/dry".

It is abundantly clear severe droughts have become much less common in the last two or three decades, when measured this way.

Previous severe episodes stick out, including the 1910s and 1950s, in addition to the better known dustbowl years.

We can get a more exact picture from the regional precipitation trends:

 

https://www.ncdc.noaa.gov/cag/regional/time-series/101/pcp

 

Generally speaking, most regions exhibit earlier periods of drought far more severe than anything seen in recent years. The only real exception is the West, which shows little in the way of any trends at all. (Contrary to wildly inaccurate claims about the recent Californian drought).

Interestingly though, earlier droughts don’t always occur at the same time in different regions. For instance, the worst drought in the Northeast occurred in the 1960s, while by far the worst drought in the South was during the 1950s, a time often ignored but arguably as bad as the 1930s.