Thiruvananthapuram | Kerala has recorded a 33 per cent deficit in southwest monsoon rainfall so far this season, with Wayanad registering the highest shortfall of 64 per cent, IMD officials said.

Only four districts -- Thiruvananthapuram, Kollam, Pathanamthitta and Thrissur -- have received normal rainfall so far during the monsoon season, India Meteorological Department (IMD) Director-in-Charge V K Mini told PTI.

She said some of these districts too could slip into the deficit category if the rainfall shortfall continues in the coming days.

As per IMD norms, a district is classified as rainfall deficient when the shortfall exceeds 19 per cent.

The rainfall deficit has already started affecting the farming sector, with the Agriculture Department advising farmers to adopt remedial measures following the IMD's forecast of below-normal monsoon rainfall this season due to the El Nino phenomenon, she said.

Mini said the impact would be more severe in rain-fed agricultural areas, as inadequate rainfall affects soil moisture and delays sowing operations.

"Normally, June witnesses two depressions and up to five low-pressure systems over the Bay of Bengal. This year, not a single depression has formed over the Bay of Bengal in June," she said.

According to her, these systems help strengthen monsoon winds and enhance rainfall over large parts of the country.

Kerala usually experiences two each depression systems during June and July-August and one in September, but the prevailing El Nino conditions may reduce the formation of such systems, she said.

Mini said the period between June 21 and July 4-5, known in Kerala's traditional agricultural calendar as "Thiruvathira Njattuvela", is considered the most favourable for planting saplings and sowing paddy.

"This period normally coincides with the peak phase of the southwest monsoon. However, El Nino has adversely affected this crucial agricultural season," she said.

She also warned that prolonged rainfall deficiency could lead to groundwater depletion and drinking water shortages.

"Based on the rainfall data released by the IMD, other departments should initiate timely measures to mitigate the cascading impacts of reduced rainfall. We had already forecast a deficient southwest monsoon this year due to the El Nino effect," Mini added.