Sunday, May 6, 2012

Drought Worsens in South Carolina

Droughts are hard to define.  Meteorological droughts are prolonged periods with less than average precipitation, but the prolonged period is nebulous.  How many weeks or months must go by before a drought is declared?  Again this depends on how much precipitation has occurred.  Obviously if no precipitation occurs then it doesn't take long to enter a drought.  Defining when a drought started can also be difficult.  Thus, you often do not know that you are in a drought until it gets serious.

Remember December 2009?  The precipitation total for that month in Columbia was 9.31 inches, almost three times the normal value.  It was a record wet December.  In addition the four month of September through December totaled 25.96 inches which was a record for that four month period.  What happened?  A strong El Nino was in progress and most of the rain that year came in just that four months.

Click on image for the larger version.
In the 28 months since that time there have only been four months of above normal rainfall.  So in retrospect we have been in a period of drought since January 2010.  The rainfall deficit has been enormous during this time.  The deficit in Columbia has reached 25.57 inches in the past 28 months.  However, it is much worse along the Savannah River where Augusta has amassed a deficit of 38.71 inches in the same time period.  Thus the western part of South Carolina is in worse shape than the northeastern part of the state and this is reflected in the USDA Drought Monitor.

Image Credit: SCDNR

The state Drought Response Committee looks at a great deal of information to come up with their drought designations.  The latest drought declaration is shown on the map to the right.

According to Hope Mizzell, S.C. State Climatologist, the winter and early spring have been dry with most locations receiving less than 65 percent of normal rainfall, "Rainfall during this time of year is crucial for adequate recharge which did not occur. As we move into late spring and summer it takes normal rainfall just to keep up with evapo-transpiration and increased water demand."

Click on image for a larger version.

The worst area in the region is central and southern Georgia.  Much of the area has been in an extreme or exceptional drought most of the year.  Even now 71% of Georgia is experiencing such conditions.  This is having an effect on agriculture and some areas are already experiencing voluntary water restrictions.

La Nina has been in progress for much of that time, but now the La Nina has ended.  Neutral conditions are expected through the summer, but there are signs that El Nino will return toward the end of the year.  This may help bring the region out of the current drought, but it is not a guarantee.

A fading La Nina.  Image Credit: NOAA.

The month of April looked grim until the 21st-22nd.  A large area of showers and thunderstorms rolled through the region.  Columbia saw 1.25 to 1.8 inches of rain.  A few spots in the Pee Dee region and in the low country of South Carolina saw as much as 3.5 inches of rain.  However, there were large areas in the Piedmont and Upstate that missed much of the rain.  The same is true for some of the coastal areas.

Observed rainfall for South Carolina for the 24 hours ending at 12z (8 a.m.) April 22.  Image Credit: NOAA.

So what is expected into the summer?  There are signs that there will be some rain over the next two weeks.  However, it will be spotty due to the fact that it will likely be from thunderstorms.  The general area is still likely to be below normal.  May will be critical for crops and if there is not enough rain, many fields will suffer.  The rainy season does not kick in until sometime in June and can sometimes be delayed into July.  It will take a number of days of daily thunderstorms to ease the situation.

In the meantime, this will strangely make us more proned to flash flooding.  The ground is hard and the heavy rain will run off rather than soak in the ground.  This is what happened last May in Columbia and the most flood proned area will be Rocky Branch Creek through Five Points and the university.

Below are the precipitation records for Columbia, SC and Augusta, GA courtesy of the National Weather Service Forecast Office in Columbia, SC.



                    TOTAL       NORMAL      DIFFERENCE
JANUARY 2010        3.18         4.66         -1.48  
FEBRUARY            2.88         3.84         -0.96 
MARCH               2.34         4.59         -2.25     
APRIL               0.91         2.98         -2.07  
MAY                 2.10         3.17         -1.07 
JUNE                4.20         4.99         -0.79 
JULY                7.70         5.54         +2.16 
AUGUST              5.56         5.41         +0.15 
SEPTEMBER           1.94         3.94         -2.00 
OCTOBER             1.83         2.89         -1.06 
NOVEMBER            1.46         2.88         -1.42 
DECEMBER            1.40         3.38         -1.98 
ANNUAL             35.50        48.27        -12.77

JANUARY 2011        1.70         4.66         -2.96 
FEBRUARY            4.21         3.84         +0.37 
MARCH               4.00         4.59         -0.59
APRIL               2.76         2.98         -0.22 
MAY                 2.74         3.17         -0.43
JUNE                2.87         4.99         -2.12
JULY                6.17         5.46         +0.71
AUGUST              4.01         5.26         -1.25 
SEPTEMBER           3.36         3.54         -0.18
OCTOBER             2.01         3.17         -1.16
NOVEMBER            1.68         2.74         -1.06
DECEMBER            1.11         3.22         -2.11
ANNUAL             36.62        44.59         -7.97

JANUARY 2012        1.76         3.58         -1.82
FEBRUARY            2.46         3.61         -1.15
MARCH               2.21         3.73         -1.52
APRIL               2.28         2.62         -0.34


                    TOTAL       NORMAL      DIFFERENCE  
JANUARY 2010        5.39         4.50         +0.89 
FEBRUARY            2.37         4.11         -1.74 
MARCH               3.20         4.61         -1.41 
APRIL               1.20         2.94         -1.74 
MAY                 1.36         3.07         -1.71 
JUNE                2.19         4.19         -2.00  
JULY                5.86         4.07         +1.79 
AUGUST              2.04         4.48         -2.44 
SEPTEMBER           1.89         3.59         -1.70 
OCTOBER             0.67         3.20         -2.53 
NOVEMBER            1.30         2.68         -1.38 
DECEMBER            1.17         3.14         -1.97 
ANNUAL             28.61        44.58        -15.97

JANUARY 2011        2.11         4.50         -2.39 
FEBRUARY            4.31         4.11         +0.20
MARCH               5.45         4.61         +0.84
APRIL               1.93         2.94         -1.01
MAY                 2.50         3.07         -0.57
JUNE                1.98         4.19         -2.21
JULY                4.05         4.33         -0.28
AUGUST              1.19         4.32         -3.13
SEPTEMBER           1.56         3.22         -1.66
OCTOBER             1.47         3.27         -1.80
NOVEMBER            1.63         2.82         -1.19
DECEMBER            1.28         3.39         -2.11
ANNUAL             29.43        43.57        -14.14 

JANUARY 2012        1.40         3.91         -2.51 
FEBRUARY            1.12         3.92         -2.80
MARCH               2.28         4.18         -1.90
APRIL               1.45         2.84         -1.39