CHARLOTTE, NC (WBTV) - It's no surprise to anyone at this point that we desperately need rainfall, and we show you on a fairly frequent basis what the current rain deficit is (currently 5-6" around Charlotte).
But this is just the yearly rain departure from average, and is not an exact measurement of the amount of rain it would take to end (or even alleviate) the drought. Although the two numbers are obviously related, there is more that goes into calculating the second one, because drought is a state of dryness.
The Drought Index tries to estimate the supply and demand of soil moisture. To do this, factors such as evapotranspiration (how much water is transferred from the land to the atmosphere) are considered in addition to temperature and amount of moisture in the soil.
The Drought Index (known formally as the Palmer Drought Severity Index - or PDSI) spans a scale from -10 (dry) to +10 (wet).
A moderate drought is when PDSI values range from -2.00 to -2.99
A severe drought is when PDSI values range from -3.00 to -3.99
An extreme drought is when PDSI values range from -4.00 or below
There are currently parts of North and South Carolina under all of these levels of drought.
The National Climatic Data Center (NCDC) puts out a nifty tool that does the calculation of how much rain we would need to end drought conditions (defined as PDSI value greater than -0.5) and ameliorate drought conditions (defined as PDSI value greater than -2.0).
According to the first map, we would need between 9-12 inches of rain in a 1 month period to eliminate the drought conditions across our NC counties (blue area). To ameliorate the drought, we would need 3-6" (red) or 6-9" (orange), depending on the location. There is also a separate map (not pictured) which shows the probability of this happening... and the chance of ending the drought in a 1-month period is less than 4.4%.
Yesterday the city began voluntary water restrictions, and there are mandatory restrictions that began last week for Beech Mountain. At this point, we'll take any rain we can get... but the short term rain chances are not looking promising.
Fore more information and to see more maps like this, click here.