MUMBAI, July 31 (Reuters) - India is likely to receive below-average monsoon rainfall in August after recording average rainfall in July, the weather department ‌said on Friday, raising concerns about crop yields and economic growth in ‌Asia's third-largest economy.

The monsoon delivers about 70% of annual rains to replenish crucial water sources in the nearly $4-trillion ​economy, where almost half of farmland lacks irrigation and about half the population earns its livelihood from farming.

Rainfall in August is likely to be below 94% of the long-period average, Mrutyunjay Mohapatra, director-general of the India Meteorological Department, told a press conference.

Cumulative rainfall in August ‌and September, the second half ⁠of the four-month monsoon season, is forecast to be below 94% of the long-period average, Mohapatra said.

Moderate El Nino conditions are prevailing ⁠and are expected to strengthen gradually, with the weather pattern likely to become strong by September, he said.

El Nino is a climate pattern marked by unusually warm sea surface temperatures in ​the central ​and eastern equatorial Pacific, which disrupts global ​weather patterns and can bring drier ‌conditions to parts of Southeast Asia and other regions.

In the past, India has experienced below-average rainfall during most El Nino years, sometimes leading to severe droughts that destroyed crops and forced authorities to limit the export of some grains.

India received 1% more rainfall than the long-period average in July, helping narrow the monsoon rainfall deficit since the season ‌began on June 1 to 12.6% from 35.4% ​at the end of June.

"The rains picked up in ​July, which helped farmers catch ​up on planting after delays in many areas," said a Mumbai-based dealer ‌with a global trade house.

"But if ​rainfall is below normal ​in August, it could affect the growth of the crops that have just been planted."

Summer crop sowing was nearly a quarter lower than a year earlier ​at the end of June, ‌but the shortfall has since narrowed to less than 5%, according to data ​compiled by the Ministry of Agriculture and Farmers' Welfare.

(Reporting by Rajendra Jadhav ​and Sakshi Dayal; Editing by Ros Russell)