Day 1 of this series on Operational Context covered earthquakes. The response to the first of this multi-part series was incredible – over 2,000 views of the post from yesterday on earthquakes. I have only been blogging for a few months, so not used to this level of traffic yet, and was completely amazed at the incredible response you’ve given to this series. I’m used to many fewer visitors each day, but then all of a sudden this “extreme event” occurred. Time will tell whether this is a pattern, but it is my hope that you have connected and will continue to connect with the topics that are discussed. Regardless, thank you for taking the time out of your day to learn and share your feedback on my posts.
I share these thoughts on yesterday’s blog activity because it really mirrors the point of this series as well as today’s topic. There are times where we go for a long period of time without major disasters, and other times where we experience event after event one after another. In my home state, we had a record setting earthquake and a major hurricane within a few days of one another. Several years ago, we had back to back major snow storms dumping feet of snow on the many parts of the state. And there are other periods where you may go several years without a major event.
History doesn’t always teaching us lessons in “neat packages” with back to back events to let us lean and immediately apply for the next disaster. This is especially true when it comes to hazards that we face which may rear their ugly head only a few times each generation. Such is the case with drought. Most of us know stories about droughts from the Dust Bowl in the 1930’s or the Southwest US in the 1980’s and 1990’s. Those of us who have more awareness of history outside the United States also know of major droughts in places like Australia, China, and many parts of East Africa including Ethiopia, Kenya, Rwanda, and so many other countries.
Most of us who have seen Geographic Information Systems (GIS) or maps that depict drought are used to seeing the US Drought Monitor. The image below will likely look familiar to you (feel free to click on the image to go to the US Drought Monitor Website). But the challenge with this website is that it only goes back to the turn of the century (21st century) with data starting in the 1999/2000 time period. The nice thing about this site is that the authors have assembled many great links for use in GIS programs and platforms (ArcGIS Online, Google Earth / Maps, etc) Archived KML, SHP, GML, WMS and other feeds as well as statistical assessments by state are available from the USDM Archive Site – http://droughtmonitor.unl.edu/dmshps_archive.htm.
So, we have pretty good information on history of droughts since 2000, but what does that really do to help us prepare for extreme droughts that we have faced in the past, but we haven’t seen in the past decade? This is where collaborative intelligence comes into play. Where do other websites or data streams exist that point to drought? Perhaps it is a temperature record? Well, it could be hot AND doesn’t have to be dry. There are differences between Florida and Arizona and both have extreme temperatures, so that correlation doesn’t work. What about looking at rainfall amounts from NOAA or other global observation networks? This could be helpful, however it would require going through a large amount of data to figure out what is “normal” and what constitutes a drought.
There is another option though. What about stream gages? The United States Geological Service (USGS Social Media Site) maintains data on thousands of stream and river gages, with many of them dating back at least to the early 20th century. These gages are usually used by emergency managers to look at flooding conditions, but can they also be used to point to an absence of flooding?
Note: a future post in this series will be looking at Flooding – come back later this week for that post in the series.
A few months ago, I discovered a tool from USGS that creates a historical raster (basically a graphic / picture) showing how high (or low) the water was throughout the history of the gage. This lets you quickly identify extreme events (both high and low) and visually correlate those events to the historical timeline, allowing you to discover new information that you wouldn’t have been able to see before. You can try creating your own graphic at http://waterwatch.usgs.gov/new/index.php?id=wwchart_rastergraph.
To start though, let’s look at the following example from Alameda Creek near Niles, CA. This USGS Gage (raw data available from USGS at http://waterdata.usgs.gov/usa/nwis/uv?11179000) has a history dating back to the late 1800’s. The Raster Hydrograph below shows periods of high and low flow events. Note the dramatic change around 1962 (we’ll get back to that in a second). Also note how much of the area has blues and greens since 1962 with a few exceptions. First off, there is a period of yellow and orange showing up in the mid 1980’s, but generally speaking, this area has more water flowing by the stream gage in the winter / spring months, and drier conditions exist from the summer into the fall.
But what in the world is going on before 1962? This graphic allows you to ask that question, so let’s go to our trusty search engine and see what the results show.
(You can try this too – Google Search for ‘alameda creek niles california 1962’ returns the following USGS report as the 5th search result which is a USGS Water Data Report – 11179000 Alameda Creek near Niles, CA. In that report, the following quote is made:
REMARKS.–Records good except for estimated discharges, which are fair. Flow regulated since 1916 by Calaveras Reservoir, although dam not completed until 1925, usable capacity, 96,800 acre-ft, most of which is diverted for San Francisco water supply; since February 1965 by San Antonio Reservoir, capacity, 51,000 acre-ft; and since September 1968 by Del Valle Reservoir, 23 mi upstream, capacity, 77,100 acre-ft. Natural flow of stream affected by water imported from Delta-Mendota Canal beginning in 1962.
Wow! So, the graphic really does work. It pointed to the 1962 time period as a dramatic change in the stream conditions. That led to a Google search result which showed that a canal began to import water from another part of California in 1962 (an aqueduct). Now you could very easily ask, “Does that show there hasn’t been a drought since 1962?” That’s far from the truth. Since there is an aqueduct, the drought conditions won’t be as apparent, so you could select another gage in the area – hopefully one that does not have diverted water. If that gage can be found you could very easily pick similar low streamflow years to identify the years of extreme drought.
Let’s take a look at a gage closer to my neck of the woods – The Potomac River at Point of Rocks, MD. In the image below you can clearly identify the blue and red values which represent the extreme water levels (high and low respectively). Long lines of red show extended periods of low streamflow which point to drought.
- Mid 1960’s
In a related article on drought from The History of Loudoun County, Virginia at http://www.loudounhistory.org/history/drought-1930-history.html, they speak to several time periods where drought was seen in the area. The article states,
There have been four major Statewide droughts since the early 1900’s. The drought of 1930-32 was one of the most severe droughts recorded in the State. Recurrence intervals ranged from 30 years to greater than 80 years. The droughts of 1938-42 and 1962-71 were less severe; however, the cumulative streamflow deficit for the 1962-71 drought was the greatest of the four droughts because of the duration of this drought. The drought of 1980-82 was the least severe and had the shortest duration.
Comparing these droughts to the image above, you can very clearly see the correlation. If you want to try this for another gage in your state, look up the gage ID
- Make your own raster hydrograph – http://waterwatch.usgs.gov/new/index.php?id=wwchart_rastergraph
- Look up USGS Gage ID – http://waterwatch.usgs.gov/new/index.php?id=ww_current
Tomorrow’s post will look at Operational Context: Flooding