Despite recent rains, the 3-year-old drought is drying up earnings for the Tennessee Valley Authority.

The federal utility’s leaders said the lack of rain needed to refill its reservoirs cost $231 million in higher power generating costs during the first five months of the current fiscal year and is a key reason why TVA doesn’t expect to meet its earnings target this year.

TVA President Tom Kilgore told directors this week that hydroelectric generation from TVA’s 29 power-producing dams has been only 45 percent of what was budgeted this year.

“In spite of all the rain we have gotten in the past few days — and we’re certainly thankful for that — our reservoirs are still not full,” Mr. Kilgore said. “Until they fill up, we will not be able to have normal hydro production.”

Rainfall in Chattanooga last month totaled more than 6.5 inches, or about a half inch more than normal, according to the National Weather Service. April showers this week provided another inch of rain to keep precipitation so far this month above normal.

But so far this year, rainfall is still more than 2 inches below normal in Chattanooga following drier-than-normal years in both 2006 and 2007.

Craig Carpenter, a program leader for the National Weather Service in Morristown, Tenn., said the weather service expects normal to slightly above normal rain this spring.

“It’s not likely to be enough to catch up the deficits we’ve seen in recent years,” he said.

After three days of scattered rain this week, Chattanooga’s weather is expected to clear today and be dry the rest of the weekend, Mr. Carpenter said.

TVA began refilling reservoirs last month to reach summertime pools by early May, but most of the tributaries to the Tennessee River remain below normal, Mr. Kilgore said.

Hydropower is TVA’s cheapest source of power generation and often provides up to 10 percent of TVA’s electricity supply. But during the current drought, hydropower has been less than half its usual share of power generation, and TVA has had to buy more expensive power on the grid to make up for the shortfall.

TVA is buying 40 percent more power from other sources this year than what was budgeted even though overall electricity sales were 3 percent below what was expected in the first half of the utility’s fiscal year.

“We expect that our earning this year will be short of what we projected,” Mr. Kilgore told the TVA board Thursday in Knoxville. “We’re not for-profit, but this is a critical measure of how much we can reinvest in our system.”