Kerala receives most of its annual rainfall during two monsoon seasons; Southwest monsoon season (June to September) and Northeast monsoon season (October to December). The State averaged season rainfall in both the seasons during the past 121 years (1901-2021) show a decreasing trend of about 10% of LPA/100 years. During 2021, the State received the southwest monsoon season rainfall within the normal range but 10.4% below its long-period average (LPA). On the other hand, the season averaged rainfall received during the Northeast monsoon season was exceptionally high (114.8% above LPA). The lowest and highest ever state averaged southwest monsoon season, rainfall was in 1981 (43.4% below LPA) and 1924 (79.9% above LPA) respectively. In case of Northeast monsoon season, the State averaged season rainfall received during 2021 was highest ever in record since 1901. This was followed by 2010 (72.4% from LPA) and 1977 (69.9% from LPA).
During southwest monsoon season rainfall for the period 1901-2021, decreasing trends was observed in all the districts except in Idukki, where increasing but in significant trend was seen. Among the districts showing decreasing trends, rainfall trends over 3districts from south (Alappuzha, Kollam and Pathnamthitta) and 4 districts from north (Kannur, Wayanad, Malappuram and Palakkad) were significant. In case of Northeast monsoon season also decreasing trends in seasonal rainfall was seen in all the districts except in Kasaragod (non- significant increasing trend), with significant decreasing trends in Palakkad and Kottayam.