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 May 14, 2009 — Precipitation remains below average for the year, but the rains of the past month and a half have substantially increased the groundwater reserves, according to a University of Virginia climatologist.

"The situation in the western half of the state, including the Charlottesville area, has improved immensely since the end of March," said climatologist Philip J. "Jerry" Stenger, the University of Virginia's climatologist. "In the eastern part of the state the levels are still far below normal."

Groundwater levels are critical because as temperatures rise, both evaporation and water demand increase; groundwater recharges the reservoirs. Underground water reserves are also vital for individual wells.

Most groundwater recharging happens during the coldweather months, when plants are dormant and water use is down. Precipitation was not far below normal levels for this winter, but there was a substantial deficit in groundwater levels to remedy.

Stenger said the area received about 3.32 inches of rain in April and has received another 3.74 inches so far in May. April's rainfall was normal compared to the long-term average for the month, and May's rains have been about double the long-term average.

"So far for 2009, we've gotten 12.84 inches of rain, which is about 80 percent of average," he said. "But the big indicator is the groundwater levels, which are normal or above average locally."

Stenger said the timing of the rain was important. It came before the growing season started in earnest, and because the temperatures have been about five degrees below normal, there was less evaporation.

Stenger said many days of rainfall came from a cold front stalled over Virginia. While that front is gone, he said it is likely that there will be heavy rain and thundershowers this weekend.

The local reservoirs were full as of Wednesday, according to the Rivanna Water and Sewer Authority.