Rainfall
 
An analysis of the rainfall statistics for the shore areas during 1977-84 clearly establishes two distinct factors :
a.

A vigorous south-west monsoon and
b.
 An intense retreating monsoon when coupled with high depressions/cyclones can cause natural hazards.

It is observed that under the influence of the southwest monsoon, the rainfall distribution pattern establishes two clear zones

  1. The North and Central zones of the shore areas receives over 60% of the total rainfall for the year, ranging between 500-700 mm.
  2. The southern zone with the two districts of Prakasam and Nellore, receives barely 300 mm rain, constituting about one-third of its total annual rainfall.
  3. The north - east monsoon however, establishes three zones
  1. The southern districts (Nellore and Prakasam) receive 60% of their annual rainfall during this monsoon.
  2. the central zone (Guntur, Krishna, East Godavari and West Godavari) receives 30% of annual rain and
  3. Less heavy northern districts (Vizianagaram, Visakhapatnam and Srikakulam) receive barely 20% of their annual rainfall.

The importance of the occurrence of rainfall and its distribution pattern is realised when it is examined in reference to the cyclonic weather patterns. Tropical cyclones normally occur during May and November. The history of cyclones over the last 100 years indicates that November is more cyclone prone than May. Therefore, the intensity of a retreating monsoon coupled with full rivers and tanks can have disastrous consequences. The rainfall regime has, therefore, to be examined together and in conjunction with other environmental factors in order to understand its full impact. It is only such a basis that can justify, the zoning of the shore areas into three distinct parts - the Northern districts comprising of Srikakulam, Vizianagaram and Visakhapatnam, the central delta districts of East and West Godavari and Krishna and the Southern districts of Guntur, Prakasam and Nellore. The rainfall pattern has in no small measure contributed and influenced the agro-economic conditions in each zone.

It can be observed from the table given that 52.5% of the total annual rainfall is received under the south west monsoon while 38.7% is received under the north east. On an average, however, all zones get one-third of the total rainfall, with the central zone receiving a little more.The monthly rainfal statement shows the highest rain during the months of August and September, while under the influence of the north-east, the month of November receives the maximum. On an average, there are 45 to 55 rainy days in a year.

 
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