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Show 8 Mr. EUBANK. Congressman, we will do anything you want. It might fit logic a little better if Dr. Potter went first to set the stage, but any way you want. Mr. CANNON. That would just be fine. Dr. Potter, if you would like to begin, that would be great. STATEMENT OF DR. THOMAS D. POTTER, DIRECTOR, NOAA COOPERATIVE INSTITUTE FOR REGIONAL PREDICTION, UNIVERSITY OF UTAH; FORMER DIRECTOR, WESTERN REGION, NATIONAL WEATHER SERVICE, NOAA Dr. POTTER. Thank you, Mr. Chairman. I would like to give a brief summary of my written remarks. Drought originates as a deficiency in precipitation over an extended period compared to the long- term average. There are some 120 different definitions but it still originates as a deficiency in precipitation over this extended period. It is a common recurring feature of climate but it's a temporary feature that's distinct from aridity which is a permanent feature. In Utah, the West Desert is arid and the rest of the state can and does have a drought over certain periods. Drought is measured by the amounts of rainfall, snowpack, streamfiows, and other water indicators compared to the averages. There are lots of data points here. In order to simplify the analysis of these thousands of bits of data, climatologists have devised indexes where a single number represents all the data in one reasonably easily understood value showing the severity and duration of a drought. There's several different drought indices but I am going to talk about only two. The first is the Palmer Drought Severity Index first devised in 1965 and since used by the U. S. Department of Agriculture and others. Figure 1 shows a series of the PDSI calculated back to 1895 for the Wasatch Front. The colors in red are the drought periods. It starts over on the left. Mike, can you perhaps move that up so they can see a scale. Maybe they won't- There it is. The top scale starts in 1895 and the second one runs from- I can't see it very well here- but I think it is 1920 and so forth. They're 25 year blocks. All the red blocks are droughts. You can see in the 1930' s the extended drought, in the 1950' s as well, and the 1980' s. The next slide is an example of the second standardized- is the Standardized Precipitation Index. That picks up drought much quicker than the PDSI by several months. You can see in the Southwest United States the reddish- orange colors in Southern Utah and Southern California, and other places, and the brown over most of Utah as well, snowing that there are very severe drought problems. A common question is how does the current drought compare to the past droughts. Weather instruments have been deployed for about a hundred years or more, so we have these PDSIs, as I showed in the first one, for back to 1895. Figure 3 shows similar data for Northern California. Those will not match up exactly with those in the first one that I showed for Utah because it is in a different location but it does show that even a reasonably wet place |
