The district wise monthly rainfall data for all the districts of Andhra Pradesh recorded during the years 1971-2009, as available in the database at CRIDA, Hyderabad were used in the present study. The rainfall totals for the summer (March to May), southwest monsoon (June- September), Rabi (October-December) and winter (January-February) seasons were computed year wise for all the districts and state as well.
The monthly temperature data for all the years 1981-2009 recorded at 21 stations spread throughout the state is available with the Agromet Databank of the Central Research Institute for Dryland Agriculture, Hyderabad were analyzed to find the mean seasonal maximum and minimum temperature as well as average diurnal range of
the temperature during different seasons considered.
Figure 4. Location map of selected stations in Andhra Pradesh for which temperature data was considered in the present study
The area, production and productivity of total food grains, rice, pearl millet and groundnut in different districts of Andhra Pradesh for the years 1981 to 2009 were obtained from Directorate of Economics and Statistics, Government of Andhra Pradesh, Hyderabad. The year wise yields of castor, pigeon pea and chickpea in Andhra Pradesh for the years 1990 to 2007 were also considered. According to Jan Null (2011), the Oceanic Nino Index (ONI) has become the defacto standard that NOAA uses for identifying El Niño (Warm) and La Niña (Cool) events in the tropical Pacific for the Nino 3.4 region (i.e., 5°N to 5°6, 120°-170°W).
Events are defined as five consecutive months at or above the +0.5 ° anomaly for warm (El Niño) events. The threshold is further broken down into the week with a 0.5 to 0.9 sea surface temperature anomaly, Moderate (1.0 to 1.4) and Strong (31.5) events.
For weak, moderate or strong, it must have equalled or exceeded the threshold for at least three months. Accordingly, the El Niño years were classified from 1951 to 2010 as follows:
During the period considered for the present study from 1981 to 2009, there were eight moderate and strong and two weak El Niño events out of 29 years.
- Central Institute of Dryland Agriculture