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America's Drought-Riskiest Cities

How Dry is Your City?

Scientists are warning that raging brush fires could become routine. Florida is running out of water to meet the needs of its growing population. New England water reserves are reaching record lows. Atlanta's main water supply may run dry in a few months. Boat ramps are becoming surrounded by dry land and streams are disappearing. Even the mighty Great Lakes are seeing historically low levels.

America's Drought-Riskiest Cities measures the drought severity for the 100 largest metro areas in the United States.

 

SoCal the driest, Texas the wettest

Los Angeles tops the list of drought-plagued cities, with its recent annual rainfall only 25% of normal. Other top-ten driest cities include Salt Lake City, Nashville, and Birmingham.

At the other end of the list are cities suffering from too much water. Cities in the central Texas region such as San Antonio, Dallas, Houston, and Oklahoma City have been afflicted by flood conditions this summer. Ironically, these floods which have caused deaths and property damage in Texas are the product of abnormal climate patterns that prevented the moisture-laden clouds to be carried northward to the already-parched Deep South.

Top ten drought-riskiest metro areas

  1. Los Angeles-Long Beach-Santa Ana, CA
  2. San Diego-Carlsbad-San Marcos, CA
  3. Oxnard-Thousand Oaks-Ventura, CA
  4. Riverside-San Bernardino-Ontario, CA
  5. Salt Lake City, UT
  6. Nashville-Davidson--Murfreesboro, TN
  7. Chattanooga, TN-GA
  8. Birmingham-Hoover, AL
  9. Greenville, SC
  10. Knoxville, TN

complete ranking

Current effects of the drought

The United States is undergoing a nationwide drought, producing a crisis that some scientists believe will have greater consequences than rising sea levels.

The devastating brush fires in Southern California are one side effect of this continuing drought. The Deep South is also gripped by a prolonged drought, endangering the water supply for the 4.4 million residents of the Atlanta mega-metro area.

The mighty Great Lakes are also shrinking, threatening shipping commerce due to historically low water levels. The Florida Everglades are being affected by Florida's continuing water emergency.

This drought is having a deep and lasting effect on the choices regarding where we will want to live in the future. The crisis has been growing slowly, but it is finally getting attention in the national spotlight.

DroughtScore.com

The complete database of Sperling Drought Indices have been put on the web, in a specialized site named DroughtScore.com.

Web visitors can now assess and compare the drought risk for every city, town and zip code in the United States, over 50,000 places in all.

In addition to the single drought index measuring the present drought situation in any area, DroughtScore.com also graphs the scores for the last 13 months, comparing the local area to state and national averages.

Methodology

With the Sperling Drought Index, we sought to provide an easy-to-understand measure of the current drought status by looking at the long-term effects of weather patterns. A score of 100 is the normal - scores over 100 indicate dry conditions, under 100 indicate wetness.

We used statistics from the National Climatic Data Center to create the Sperling Drought Index. We specifically considered long-term precipitation trends and patterns, and the Palmer drought indices. These metrics are particularly valuable in that they attempt to measure the duration and intensity of long-term drought-inducing circulation patterns. We used a rolling average, weighted more heavily towards recent precipitation trends.

Since the hydrological effects of drought such as groundwater and reservoir levels take longer to develop and recover, we based the Sperling Drought Index on those metrics which respond more slowly to immediate weather conditions.

Accordingly, a short-term wet spell may have little direct effect on the Sperling Drought Index.

Drought score Description
over 120 Extreme Drought
120-115 Severe Drought
115-110 Moderate Drought
110-105 Mild Drought
105-102.5 Temp Dry Spell
102.5-97.5 Near Normal
97.5-95 Temp Wet Spell
95-90 Mildly Wet
90-85 Moderately Wet
85-80 Very Wet
under 80 Extremely Wet

We created our index so that a score of 100 represents the climatic normal. Values greater than 100 represent drier conditions, and values less than 100 indicate wetter conditions.

It would not be accurate to use the Sperling Drought Index to quantify differences in drought. For example, if one place has a Drought Score of 110 compared to another with a Drought Score of 95, it would be misleading to say the place has "15% more drought," or faces a "15% greater drought risk." The effects of drought vary greatly between different places, and cannot be reduced to a single measure.

For more information about the measurement of drought, consult the NCDC resources for the Standardized Precipitation Index (SPI), the Crop Moisture Index (CMI), the Palmer Z Index, the Palmer Drought Severity Index (PDSI) and the Palmer Hydrological Drought Index (PHDI).