July Drought update: August 9, 2012

July Drought Update: August 9, 2012

The High Plains Climate Center maps indicate that Douglas County is slipping from the “extreme drought” into the “exceptional drought” category, having endured a dry summer last year, a mild winter, an early, dry spring into a July that has produced temperatures averaging some 10 degrees Fahrenheit over normal hot July temperatures and precipitation amounts less than 25% of normal. While there are some differences between the local droughts of the 1930s and the 1950s, our current drought is having a similar adverse impact on agriculture, wildlife, and water resources, even though our ability to maintain our personal comfort level has improved.

Putting our local condition in context, July temperatures for the contiguous US were the hottest ever in records that go back to 1895. It was also the hottest January-July stretch on record and the hottest 12 month stretch (August 2011 – July 2012) on record. Interestingly, 5 of the 10 hottest 12 month stretches in the US since 1895 have occurred in the past 16 months, and the other 5 records were also set since 1999, hotter than either the 50s or 30s. Alas, it was also the hottest June on record globally for land temperatures as well.

While meteorologists and climatologists caution against conflating an individual regional weather event like our current drought with global climate change, recent studies do indicate that the face of climate change includes a higher frequency of extreme weather events. In the past year, the IPCC released an in-depth study titled “Managing the risks of extreme events and disasters to advance climate change adaptation”. “Managing the risks” is almost 600 pages long, but the relevant section for this topic is in Chapter 3, which explains the difference between weather and climate. The face of climate is of course composed of weather events, but the climate itself is a composite of those events, i.e. what happens in the weather over extended periods.

A good way to describe a changing climate using weather events such as the current drought we are experiencing as the unit of measurement for that change would be to say that:

-there can be a change in the frequency of extreme weather events (example: more mild winters, more flooding, etc.)

-there can be a change in intensity of events (example: record-breaking weather events)

-there can be a change in spatial extent (examples: drought or flood covers larger area)

-there can be a change in the timing (example: change in the cycles of El Nino/La Nina)

So a drought like the one we are experiencing now in and of itself is neither unique in its extent nor its intensity (the 30s and 50s had similar droughts). But the fact that it is happening on the tail of the Texas-Northern Mexico drought last year, and concurrent with the western US drought suggests that there is something more going on. Another way to look at it as a climate-related change event is to look at the probabilities, so that what may have used to have been a 1-in-500 year event at a given place is now a 1-in-50 year probability event.

The IPCC paper delves into this pretty deeply, but going back to Chapter 3, it summarizes what weather event trends have occurred since 1950, suggesting the nature of the climate-level changes we might expect to see in the future. The period of time is relatively short when compared to the overall climatological record, so the scientific community’s level of confidence in these trends varies depending on how robust the trends are, both globally and regionally. With this in mind, the nature of changes and the levels of confidence in those trends since 1950 are as follows:

Very Likely/High Confidence

It is very likely that there has been an overall decrease in the number of cold days and nights, and an overall increase in the number of warm days and nights, at the global scale, that is, for most land areas with sufficient data. It is likely that these changes have also occurred at the continental scale in North America, Europe, and Australia.

It is likely that there have been statistically significant increases in the number of heavy precipitation events (e.g., 95th percentile) in more regions than there have been statistically significant decreases, but there are strong regional and subregional variations in the trends.

It is likely that there has been a poleward shift in the main Northern and Southern Hemisphere extratropical storm tracks.

It is likely that there has been an increase in extreme coastal high water related to increases in mean sea level in the late 20th century.

Somewhat Likely/Medium Confidence

There is medium confidence of a warming trend in daily temperature extremes in much of Asia. Confidence in observed trends in daily temperature extremes in Africa and South America generally varies from low to medium depending on the region.

Globally, in many (but not all) regions with sufficient data there is medium confidence that the length or number of warm spells or heat waves has increased since the middle of the 20th century.

There is medium confidence that since the 1950s some regions of the world have experienced a trend to more intense and longer droughts, in particular in southern Europe and West Africa, but in some regions droughts have become less frequent, less intense, or shorter, for example, in central North America and northwestern Australia.

Less Likely/Low Confidence

There is low confidence that any observed long-term (i.e., 40 years or more) increases in tropical cyclone activity are robust, after accounting for past changes in observing capabilities.

There is low confidence in observed trends in small-scale phenomena such as tornadoes and hail because of data inhomogeneities and inadequacies in monitoring systems.

There is limited to medium evidence available to assess climate-driven observed changes in the magnitude and frequency of floods at regional scales because the available instrumental records of floods at gauge stations are limited in space and time, and because of confounding effects of changes in land use and engineering. Furthermore, there is low agreement in this evidence, and thus overall low confidence at the global scale regarding even the sign of these changes.

So, what does all of this mean? Based on the IPCC report above, the trends since the 1950s have indicated a reduced frequency and intensity of droughts in central North America while places like southern Europe and west Africa have shown increased frequency and severity. My guess is that the back-to-back droughts in Texas/northern Mexico last year and points north this year may indicate that there is an increasing confidence level that droughts in the heartland will occur with at least the level of regularity that they have in the past and quite possibly even more frequent. We can say with a moderate level of confidence that we will be seeing more frequent and intense heat waves locally.

There is a high level of confidence that we will be experiencing more heavy precipitation events, milder winters and warmer summers, especially as they manifest in warmer nights in both seasons. Since Kansas has a long history of extreme weather, and climatological trends support even more extreme weather globally, don’t be surprised if you spend your life here, that you’ll get to experience pretty much every extreme kind of weather out there!

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