Climate

The State experiences tropical climate with slight variations depending on the elevation and maritime influence. The Eastern Ghats separate the Deccan plateau from the coastal belt. The plateau slopes from the interior towards the east, from elevations of less than one kilometer and is drained by two major river systems of the Godavari and Krishna which scoop out the vast low lying areas. In the south, in Chittoor, Cuddapah and Anantapur districts, the Eastern Ghats break into various ranges, namely, the Veligondas, the Nallamalas and the Palakondas, form a general plateau with elevations rising to one kilometre. In the north, in Visakhapatnam district, the Eastern Ghats are more cohesive and have higher elevations of about two kilometres. The low lying coastal belt extends to about 100 kilometres in the south and narrows to 40 kilometres in the north. The wide deltaic region of the Godavari and the Krishna forms the central part of the coastal belt. These aerographic features influence, to some extent, the climate of the State, with the plateau regions experiencing more temperate climate than the low lying valleys and the coastal belt.

Meteorological Subdivisions
The State is divided into three subdivisions:

(A) Coastal Andhra consisting of Nellore, Prakasam, Guntur, Krishna, West Godavari, East Godavari, Visakhapatnam, Vizianagaram and Srikakulam districts. Of these, Guntur and Krishna belong to the deltaic region and extend farthest into the interior to a distance of 100 to 150 kilometres, where the marine influence on climate is reduced.

(B) Rayalaseema consisting of Chittoor, Cuddapah, Anantapur and Kurnool districts.

(C) Telangana consisting of Adilabad, Karimnagar, Nizamabad, Medak, Ranga Reddy, Hyderabad, Mahbubnagar, Nalgonda, Warangal and Khammam districts.

The climate of Andhra Pradesh can be broadly classified into (1) tropical rainy and (2) hot steppe. The general characteristics of the first type are that the mean daily temperature is above 18^O C with an annual rainfall of 100 to 250 centimetres, most of it occurring during the summer south-west monsoon .
In hot steppe regions, the mean daily temperature is always above 18⁰ C. The summer, which is hot and dry, is followed by monsoon rains. In the case of this State, however, considerable rain falls outside this period also in the southern and coastal parts.

Temperature
The mean daily maximum and minimum temperatures for each of the three subdivisions are discussed below:

(A) Coastal Andhra Pradesh
The climate of most of the region is tropical rainy. The western portion of Guntur and its adjoining parts of Prakasam belong to the hot steppe type, and this area is warm throughout the year. The mean temperature is always above 22⁰ C. During the hottest part of the year, from April to June, the mean temperature ranges between 29^oC and 35^OC, increasing towards the interior and the south. With the onset of the south-west monsoon, the temperature falls appreciably, particularly in July.

The mean maximum temperature ranges from 27^o C to 30^o C in January and from 34^oC to 41^o C in May which is the hottest month. The maximum temperature generally increases towards the interior and the south along the coast. Maximum temperature of 47^o C to 48^o C has been recorded in a number of stations. Nidadavole recorded the highest temperature of 48.9^oC on the 26th of May, 1962 in the whole of Andhra Pradesh.

The mean minimum temperature varies widely from 17^o C to 20^o C in December, which is the coolest month, to 27^o C or 28^o C in May and June. The mean minimum temperature increases from north to south along the coast and also from the coast to the interior. The lowest minimum on individual days ranges from 10^o C to 14^o C.

The mean diurnal range of temperature for the year as a whole in the coastal stations is 8^o C to 10^o C which increases to 12^o C in the interior. The maximum range is generally in March and it is 15^o C over the area away from the coast and 9^o C to 11^o C along the coast with an increase towards the south. The minimum range of 7^o C to 9^o C occurs in the monsoon month of July.

(B) Rayalaseema
The climate of this region is warm all through the year and is classified into hot and dry steppe types excluding Chittoor district which comes under the tropical rainy type but has considerable rainfall from October to December. The mean temperature is always above 23^o C over the plains and above 20^o C over the elevated area to the south. During April and May, the hottest part of the year, the mean temperature ranges between 32^o C and 35^o C over the plains. At Arogyavaram, an elevated station, the mean temperature is 29^o C. With the onset of the south-west monsoon, the temperature falls considerably to 28^o C in July over the plains.

The mean maximum temperature ranges from 30^o C in December to 40^o C in May, decreasing considerably with the elevation over the southern hilly region. The maximum temperatures of 45^o C to 47^o C were recorded on individual days except over the plateau area in the south where less than 40^o C is recorded.

In December and January, the mean minimum temparatures are the lowest being 17^o C to 19^o C over the plains, and they decrease over the plateau region where the mean minimum temperature does not exceed 25^o C even in summer. Temperature as low as 7^o C was recorded on individual days, particularly in the northern parts of the subdivision.

The mean diurnal variation of temperature for the year as a whole is 10^o C to 12^o C. The maximum variation of 13^o C to 15^o C occurs in February and March, the least being 9^o C during the monsoon months of July and August.

Over the plains, the climate is generally comfortable from November to January. April and May, being hot and dry are uncomfortable. June and July also remain uncomfortable due to increased humidity. The plateau region is relatively more comfortable throughout the year and pleasant from November to February.

(C) Telangana
Tropical rainy climate prevails over most of Telangana, hot steppe type being confined to Mahbubnagar, Hyderabad and Nalgonda districts. Telangana is the hottest part of the State during summer and coldest in winter. The mean daily temperature varies from 30^o C to 36^o C from April to June and from 20^o C to 24^o C in the months of December and January.

The mean maximum temperature ranges between 40^o C and 43^o C in May. On individual days, the maximum temperature had touched 47^o C in most parts of the region. After the withdrawal of the monsoon, the maximum temperature rises slightly due to increased insulation.

The mean minimum temperature is 13^o C to 17^o C in December and January, but it rises to 26^o C to 29^o C in May. The minimum temperature falls rapidly after October, and less than 10^oC was recorded on individual days. Nizamabad had recorded the lowest temperature of 4.4^o C on the 17th of December, 1897 in the entire State.

The mean diurnal variation is 12^o C for the year as a whole. It is 13^o C to 15^o C in February and March, and 8^o C in the monsoon months of July and August.

The climate is pleasant from November to February. The summer months of April and May are uncomfortable due to oppressive heat. The period from July to September is warm, humid and uncomfortable.

Rainfal
The annual rainfall varies from less than 60 cm., in western Rayalaseema to more than 100 cm., in the north and north-eastern parts of the State, and reaches 150 cm., close to the north-eastern border. Except Telangana, the State receives substantial rainfall during the north-east monsoon period also. It is specially so in the southern coastal belt which receives 50 to 75 cm., from October to December. The unbroken range of Eastern Ghats rising steeply about 40 km., inland in Visakhapatnam district and its neighbourhood, exert significant influence on the rainfall and its distribution. These act as a barrier to the rain-bearing easterly winds blowing in association with the depressions from the Bay of Bengal during the south-west monsoon. The rainfall here increases towards the west from 100 cm., (near the coast) to 150 cm., (along portions of the northern boundary), while it decreases over the rest of the State. The heaviest rainfall recorded in the State in 24 hours was 51 cm., at Gajapatinagaram on the 14th of October, 1931.

Coastal districts
The annual rainfall is 70 to 150 cm., The coastal belt north of 16^o C latitude is the area with maximum rainfall i.e.., 100 to 150 cm. Nellore district receives 50 to 60 per cent of its rain from the north-east monsoon in October and November, each accounting for 25 per cent of the annual fall, while only 30 per cent is received during the south-west monsoon. The rest of the subdivision receives 60 per cent in the south-west monsoon. The advent of the north-east monsoon is conspicuous over the southern coastal belt where the rainfall rises from 11 cm., in September to 23 cm., in October.

In the month of July, it rains in the central coastal belt, in September, in the northern districts of Srikakulam and Visakhapatnam, and in November in the southern districts of Guntur, Prakasam and Nellore.

Rayalaseema
The rainfall over the western part of this subdivision is less than 60 cm., Anantapur and Kurnool districts recording as low as 55 cm. This is the most dry part in the whole State. Most of Rayalaseema gets 30 to 50 cm., of rain during the south-west monsoon season (June to September). This is 40 to 70 per cent of the annual fall. Rainfall during the north-east monsoon period, October to December, is less than 15 cm., in the north-west and it increases to 50 cm., in the south-east. The rainfall during this period is 20 to 40 per cent of the annual rainfall. September is generally the month when it rains and for Chittoor district it is October.

Telangana
The annual rainfall increases from less than 75 cm., in the southern half to over 100 cm., in the northern half. More than 75 per cent of it is received during the south-west monsoon season, i.e., from June to September, July being the month when it rains. But in the south-western district of Nalgonda, Hyderabad and Mahbubnagar, September is the month, when there are rains. The south-west monsoon sets in by the 7th of June. Its advent is sudden and the rainfall increases from less than 5 per cent (of the annual) in May to 15 per cent in June.

Rainfall variability
The variability of rainfall in the south-west monsoon season is 25 per cent over Telangana and the coastal belt except Nellore district, and it rises to 40 per cent for Rayalaseema and Nellore district. The variability of rainfall from October to December is higher and it increases to 50 or 60 per cent for Rayalaseema and the coastal belt, and to 80 per cent over Telangana. The monthly rainfall is highly variable particularly in Rayalaseema and the adjoining areas.

The annual variability is about 20 to 25 per cent for Telangana and the northern half of the Coastal belt, and 25 to 30 per cent for Rayalaseema and the rest of the coastal belt.

A brief description of the meteorological installations in Visakhapatnam district is given below.

There are six meteorological installations in Visakhapatnam district. They are

(1) cyclone warning centre (opposite the Andhra University)

(2) cyclone warning radar unit at Dolphins' Nose

(3) meteorological office at the airport

(4) port meteorological office on the Fringe Road

(5) agricultural meteorological observatory at Anakapalle and

(6) evapotranspiration (E.T.) station at the Sugarcane Research Station, Anakapalle.

Excessive rainfall

It can be said that rainfall, sufficiently in excess of the normal, is a predominant factor for the occurrence of floods. For the purpose of the present description, annual rainfall exceeding 125 per cent of the normal is considered as excessive rain.

During the 50 year period from 1901 to 1950, excessive rainfall over Andhra Pradesh was as follows:

Coastal Andhra
Nellore district experienced ten years of excessive rain, out of which, rainfall exceeded 150 per cent of the normal in one year (1946). Guntur had nine such years, of which, two years (1903 and 1916) recorded rainfall of more than 150 per cent. In the remaining districts, 5 to 6 years recorded excessive rainfall. Rainfall exceeding 150 per cent of the normal occurred in 1903 and 1916 in Krishna district and in 1916 in West Godavari district.

Rayalaseema
Excessive rainfall was recorded in 7 to 9 years in the region. Chittoor district, however, experienced more than 150 per cent of normal rainfall four times in 1903, 1930, 1943 and 1946. Anantapur district experienced excessive rainfall thrice in 1903, 1916 and 1917. Cuddapah and Kurnool districts witnessed rainfall only once in 1903 and 1916 respectively.

Telangana
Mahbubnagar district had ten years of excessive rain, four of which (1903, 1906, 1916 and 1917) had rain exceeding 150 per cent of the normal. Nalgonda and Warangal had nine such years, three (1903, 1915 and 1916) being more than 150 per cent of the normal in Nalgonda and one in Warangal (1903). Khammam had eight such occasions but in two years (1903 and 1917), the rainfall exceeded 150 per cent of the normal. The remaining districts recorded excessive rain in 4 to 6 years. In the case of Hyderabad, out of 6 years of excessive rain, as many as four years (1903, 1915, 1916 and 1933) were with rainfall of more than 150 per cent. Generally speaking, 1903 was a year of more than 150 per cent of rainfall.

Depressions and storms
In late October and November, depressions and storms from the Bay of Bengal cross the State's coast or recurve towards the north or north-east and travel parallel to the coast. Heavy rains occur in the coastal belt and the interior in association with these disturbances.

The following table gives the number of depressions/storms that affected each of the three regions during the 70-year period ending with 1960. For this purpose, depressions affecting more than one sub-division have been counted separately for each sub-division. The coast is further subdivided into (1) south coast from Nellore to Ongole, (2) central coast from Ongole to Kakinada and (3) north coast from Kakinada and above to give an idea of the incidence of the disturbances over different parts of the coast. The last column gives the number of depressions, storms that affected the State as a whole during this period. For this purpose, each depression is counted as one, though it might have affected more than one sub-division.

Depressions and Storms in Andhra Pradesh From 1891 to 1960

The disturbances in the Bay of Bengal affecting Andhra Pradesh are generally rare between December and August, though the central coast may be affected in May and August once in five or six years. September to November are the principal months when the coast is much affected. On an average, at least one disturbance affects it in a year.

Pressure and Winds
During January, the atmospheric pressure is high in north India and it decreases towards the south. Over Andhra Pradesh, the pressure gradient is weak and is hardly one mb. Winds are mostly light and are east to north-easternly.

Pressure decreases, and by March, it is nearly uniform over the State. Winds are light, easternly to south-easternly and get strengthened in the evening. In April, with the establishment of a low area over Bihar and its neighbourhood, a reversal in the pressure gradient occurs. The gradient over the State, however, continues to be weak. Winds are mostly south-easternly and they become south-westernly over the northern coastal districts. With the advancement of summer, the seasonal low over north India deepens and shifts towards the north-west. The pressure gradient over Andhra Pradesh generally increases. Winds strengthen and become westernly to north-westernly except over the coast where they are south to south-westernly till September. October is a month of transition when the reversal of pressure gradient takes place. Winds weaken and take a northernly component. The seasonal low begins to establish itself over the Bay of Bengal and conditions revert to the winter pattern. Pressures thereafter continue to rise till January. Sea-breeze is generally felt over the coastal belt throughout the year, especially during afternoons and evenings.

Humidity
Humidity is high in the coastal belt throughout the year with an average of 70 to 80 per cent in the morning and it decreases in the afternoon by 10 to 15 per cent in the areas away from the coast. In the interior, the afternoon values are low and the humidity drops sometimes even below 30 per cent.

High humidity of 70 to 80 per cent prevails in the morning over Rayalaseema from July to November. The humidity is about 50 to 60 per cent in the morning and 25 to 35 per cent in the afternoon from February to May, March is the most dry month when the relative humidity drops down to less than 20 per cent in the afternoon.

In Telangana also, humidity in the morning is very high exceeding 80 per cent from July to September. In the dry months of March, April and May, humidity is generally low with an average of 25 to 30 per cent and decreases to 20 per cent at individual stations.

Cloudiness

Coastal Andhra
From May to October, the skies are covered more than half and are overcast on half of the days in July and August. The average for these two months are 6.5 and 6.2 okta (eights of sky). Clouds in winter months are minimum, being only 2 to 3 okta.

Rayalaseema
Over Rayalaseema, more than half of the sky remains clouded from May to November with an average of 6 to 7 okta. From June to September, one-third to half of the days, the skies are overcast. December to March are the months with minimum clouds of 1 to 3 okta. During these months, about a third to half of the days have clear skies in the morning.

Telangana
In Telangana, June to October is the period when more than half of the sky is covered with clouds, while only about 2/8 ths of the sky is clouded from January to March. Half of the days in July and August have overcast skies. About 10 to 13 days in the months of January, February and March, the skies are free from clouds in clear weather.

Other Weather Phenomena
Thunderstorm activity is pronounced over the State in May and June before the onset of the south-west monsoon and again in September and October in association with the onset of the north-east monsoon. The average is 4 to 6 days in each of these months. Dust storms are rare. During May, a maximum frequency of 1 to 2 days over Telangana has been observed. Fog also is of very rare occurrence.

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