Rainfall variability analysis using standardized precipitation index in arid climate of Andhra Pradesh in sub-tropical India

Rainfall is the major limiting weather parameter for crop production in tropical and subtropical regions. Its intensity and distribution across the seasons decide the success of agricultural production system in dryland areas. The historical rainfall data of Ananthapuramu district was used to analyze variability in monthly and seasonal distribution. Based on IMD criteria, the long-term rainfall data for a period of 140 years (1877-2016) was categorized as excess, normal and deficit and used for assessing the variability of monthly and seasonal rainfall. The intensity of drought was also assessed using Standardized Precipitation Index. The results indicated that Ananthapuramu district received mean annual rainfall of 550 mm with 25.1% CV during the study period. The district received excess rainfall in 31 years, normal rainfall in 76 years and deficit rainfall in 33 years. It is observed that variability in rainfall was lower for SWM and NEM as compared to CWP and HWP seasons. Among 33 years of deficit rainfall, 22 and 18 years recorded normal rainfall during SWM and NEM respectively based on SPI values. It is also observed that SWM received near normal precipitation for 69 years during normal rainfall years. The SPI analysis showed that near normal rainfall was received in 12 and 14 years during SWM and NEM respectively in excess rainfall years. It can be concluded that Standardized Precipitation Index serves as a good indicator for assessing severity of drought to plan for various activities under agricultural sector in dryland areas.