EIACP PC Hub: Kerala
State of Environment and Related Issues

             The climate of Kerala, as per Koppen's classification, is tropical monsoon with seasonally excessive rainfall and hot summer except over Thiruvananthapuram district, where the climate as tropical savana with seasonally dry and hot summer weather. The entire state is classified as one meteorological sub division for climatologically purposes. The year may be divided into four seasons. The period March to the end of May is the hot season. This is followed by Southwest Monsoon season that continues till the beginning of October. From October to December is the Northeast Monsoon season and the two months January & February winter season. The climate is pleasant from September to February. Summer months March to May is uncomfortable due to high temperature and humidity. The State is extremely humid due to the existence of Arabian Sea in the west of it.

Wind:The winds over the State are seasonal only in the region of Palghat Gap where winds are predominantly from the east in the period from November to March and from west in the rest of the year. In other parts of the State flow of wind is mainly governed by differential heating of land and water mass together with mountain winds. Winds have westerly component during the day and easterly components during the night through the year. In general winds are quite strong during afternoons when the thermal circulation is best developed and weak during night.

Humidity: As the State stretches from north to south with the Arabian Sea in its west, relative humidity is in general high over the State. In the period January to March afternoon humidity reduce to 60-63%, varying from 35% in the interior to 71 % in the coastal area. The diurnal variation in relative humidity during this period is maximum and ranges from 4 to 16%, depending upon the proximity of the sea. The relative humidity in the monsoon period rises to about 85% for the state. The variation in this period is minimum.

Temperature:Day temperatures are more or less uniform over the plains throughout the year except during monsoon months when these temperatures drop down by about 3 to 5°C. Both day and night temperatures are lower over the plateau and at high level stations than over the plain. Day temperatures of coastal places are less than those of interior places. March is hottest month with a mean maximum temperature of about 33°C. Mean maximum temperature is minimum in the month of July when the State receives plenty of rainfall and the sky is heavily clouded. It is 28.5°C for the State as a whole in July, varying from about 28°C in the north to about 29°C in the South. Inland stations experience higher maximum temperatures than the coastal stations. From May onwards both the maximum and minimum temperatures start falling, the latter very rapidly while the former slowly.

Rainfall: The total annual rainfall in the State varies from 360 cm. over the extreme northern parts to about 180 cm. in the southern parts. The southwest monsoon (June­-October) is the principal rainy season when the State receives about 70% of its annual rainfall. Monsoon rainfall as percentage of annual rainfall decreases from north to south and varies from 83 % in north most district of Kasaragode to 50% south most district of Thiruvananthapuram. Northeast monsoon rainfall as percentage of annual rainfall increases from north to south and varies from 9% in north most district of Kasaragode to 27% in south most district of Thiruvananthapuram. The rainfall amount in the State decreases towards the south with decrease of height of Western Ghats . The southern most district of Thiruvananthapuram where Western Ghats are nearest to the sea coast and its average height is also least in the State receives minimum amount of rainfall. The thunderstorm rains in the pre-monsoon months of April and May and that of monsoon months are locally known as 'EDAVAPATHI'. Rainfall during northeast monsoon season is known as 'THULAVARSHAM' in local language. The southwest monsoon sets-over the southern parts of the State by about 1 st June and extends over the entire State by 5^th June. June and July are the rainiest months, each accounting individually to about 23% of annual rainfall.Monthly distribution of Normal and Actual rainfall of Kerala state for last ten years .

         The diversity of the geographical features of the state has resulted in a corresponding diversity in climate. The High Ranges have a cool and bracing climate throughout the year, while the plains are hot and humid. The average level of annual rainfall is quite high when compared to other Indian states. The state basically enjoys 4 types of climate such as Winter, Summer, South West Monsoon and North East Monsoon.

Winter Season in Kerala

           In Kerala the winter season starts when the northeast monsoons ends. That is from the month November till the middle of February. During this time, the temperature is less but it does not have much difference with the other seasons. The temperature remains cool constantly throughout the year in the highlands but the winter temperatures falls below 10°C. It is during this winter season that we receive some of the lowest amount of rainfall.

Summer Season in Kerala

            The temperature starts to increase with the end of February which indicates the beginning of summer in Kerala. The characteristics of summer in Kerala are relatively higher temperature, less rainfall and humid weather.  The other Indian states have a temperature of about 40°C, whereas in Kerala it is comparatively cool and pleasant. It is mainly because of the presence of the Western ghats that prevents the northern wind from entering our state. The Arabian sea bordering us that gives a cool breeze which helps to make the temperature moderate. Another important feature of this season is the arrival of rain which is accompanied by thunder and lightening. The summer season extends from March till May or the beginning of June. It ends with the beginning of monsoon.

South West Monsoon in Kerala

              The rainy season in Kerala is the Southwest monsoon. In malayalam this season is called as Edavappaathi which means in the middle of the malayalam month Edavam.  It is called so because the rain starts by the middle of this month that is the end of May or early June. The following two months have torrential rain. As Kerala lies on the windward side of the Western Ghats and is the first state to get hit by the monsoon winds, this state receives heavy rainfall. It is the monsoon that provides almost 85% of the rains. The slopes of the Western Ghats receive the highest amount of rain. The rivers get flooded by the monsoons. This season continues till the end of September.

North East Monsoon in Kerala

            The North east monsoon is also known as the Retreating Monsoon or the Reverse monsoons. This hits Kerala when the southwest monsoon winds take their return. These rains are called as Thulavarsham in malayalam because it rains during the malayalam month thulam. It comes in the month October and November and at times continues up to December. The main feature of this season is heavy rains during afternoon together with lightening and thunder. The days are usually warm and humid without much variation in temperature.

               There has been a great change in the climatic condition of the Earth in the past few years. This has affected the weather conditions in Kerala also. 

• Monsoon 2012-22

Source

Economic Review 2013-2023,  IMD Thiruvananthapuram