Drought tends to be a creeping phenomenon occurs gradually with the deficiency in rainfall further extending its impact on sectors which are dependent on water. The drought characteristics were analysed in Parambikulam Aliyar Project (PAP) basin based on the European Centre for Medium range Weather Forecasts Interim Reanalysis (ERA-Interim) gridded data with resolution of 0.125° ×0.125° during 1981-2017. Reconnaissance Drought Index (RDI) was applied for monitoring the drought. The variables used in RDI are rainfall and potential evapotranspiration (ETo), the required meteorological data were taken from the ERA Interim dataset and ETo was calculated using Penman-Monteith method. RDI indicated that 41% of the time had drought condition over 37 years. Two years (1982 and 2012) faced severe drought across all the parts of the PAP basin and the highest number of mild drought events were observed than the other drought conditions in PAP basin. Results showed that Plain areas in PAP basin experienced maximum number of drought events compared to the other areas in PAP basin during the investigation period.

Drought is the major precipitation anomaly that has greater impact on water resource management, ground water table and agricultural production. The WASP index (Weighted Anomaly of Standardized Precipitation Index) was estimated for a period 1901-2019 (119 years) – four time scales (12 months, 9 months, 6 months and 3 months) based on the IMD precipitation dataset to analyse the dry events. Analysis over different time scales is necessary to find out the impact of the slowly evolving drought on the agricultural production as well as water resources. The numbers of moderate dry events were 276, 256, 188 and 100 for WASP12, WASP9, WASP6, and WASP3 respectively for the whole of 119 years data. The number of extreme dry events with WASP12, WASP9, WASP6, and WASP3 were 0, 4, 29 and 59, respectively, for 119 years. There was no specific trend in number of dry events over the study region and 1991-2019 was found to have higher number of dry events when compared with the other tri-decadal periods.

<p><strong>Abstract.</strong> Climate change induced extreme weather events such as drought and flood condition are likely to become more common and associated impacts on crop production will be more without proper irrigation planning. The present investigation was undertaken for assessing the impact of Climate change on tomato yield and water use efficiency (WUE) using AquaCrop model and RegCM 4.4 simulations. The water driven AquaCrop model was validated based on observation of field experiment conducted with four different dates of sowing (1st November, 15th November, 1st December, 15th December) at Ponnaniyar basin, Tiruchirappalli. Validation of AquaCrop model indicated the capability of AquaCrop in predicting tomato yield, biomass and WUE close to the observed data. Seasonal maximum and minimum temperatures over Tiruchirappalli are projected to increase in the mid-century under both RCP4.5 and RCP8.5 scenarios. Maximum temperature is expected to increase up to 1.7&amp;thinsp;&amp;deg;C/2.5&amp;thinsp;&amp;deg;C in SWM and 1.9&amp;thinsp;&amp;deg;C/2.9&amp;thinsp;&amp;deg;C in NEM by the mid of century as projected through stabilization (RCP 4.5) and overshoot emission (RCP 8.5) pathways. Minimum temperature is expected to increase up to 1.6&amp;thinsp;&amp;deg;C/2.2&amp;thinsp;&amp;deg;C in SWM and 1.6&amp;thinsp;&amp;deg;C/2.1&amp;thinsp;&amp;deg;C in NEM by the mid of century as projected through stabilization (RCP 4.5) and overshoot emission (RCP 8.5) pathways. Seasonal rainfall over Tiruchirappalli is expected to decrease with RCP4.5 and RCP8.5scenarios with different magnitude. Rainfall is expected to change to the tune of &amp;minus;1/&amp;minus;11 per cent in SWM and &amp;minus;2/&amp;minus;14 per cent in NEM by the mid of century as projected through stabilization (RCP 4.5) and overshoot emission (RCP 8.5) pathways.</p>

Rainfall has a greater impact on agricultural, hydrological, economic, environmental and social systems. Inconsistencies in rainfall pattern could lead to extremities like drought and flood. Drought is a long period of unusually low rainfall that severely affects crop production and welfare of the people. Understanding the impacts of drought is crucial for planning, mitigation and responses.  The Standardized precipitation index (SPI) method was employed for identifying drought occurrence in Parambikulam aliyar basin based on rainfall data of 37 years (1981–2017). SPI method indicated PAP basin had drought once in 4 years. In 19 per cent times, wet situation found to exist in PAP basin, five years exhibited moderately wet condition (1984, 1996, 2010, 2015 and 2017) and two years (1992 and 2005) fell under extremely wet event. Quantification on the drought events forms the scientific basis for decision makers to reduce the societal vulnerability to drought.

Rainfall is one of the most important climatic variables that determine the spatial and temporal patterns of climate variability of a region, which also provides useful information for the planning of water resources, agricultural production, and others. Climate change is one of the most significant worldwide issues talked among scientists and researchers, and one of the consequences of climate change is the alteration of rainfall patterns. 'India's population and the economy is linked to climate-sensitive activities, including rainfed agriculture and excess climate anomalies, deficient and flooded rainfall years have a dramatic impact on the economy as well as on the living conditions of the inhabitants of the affected region. An understanding of current and historical trends and variation is inevitable to her future development, especially in agricultural and hydrological sectors. In the present study, historical weather data for 33 years (1981-2013) was analyzed for rainfed cropping season (September - December) to understand the climatic variability in the Kanyakumari district of Tamil Nadu. The maximum daily air temperature increased on average by 0.02°C per year, whereas minimum daily air temperature remained constant during the rainfed cropping season. The high rainfall zone receives an annual and rainfed cropping average rainfall of 1307and 672 mm, respectively. Analysis of rainfall during rainfed cropping period over 33 years showed ten years had standard RF, nine years had deficit rainfall, six years had below standard RF, one year had above standard RF and seven years had excess RF. Analysis indicates that the deficit condition prevailed in every alternate year in recent decades. The onset of rainfed cropping season varied over the years (1981-2013), 13 years had onset in the slot from 1st to 5th  September, and in others, years onset occurred between 6 and 30th September. Cessation also had a variation over 33 years and 16 years had cessation from 26 to 31st December while remaining years had cessation in the period of 1-25th December. LGP ranged from 57 to 143 days, with an average LGP of 106 days.  Dry spell varied from 3 to 12 days with the mean of 6 days, and wet spell varied from 2 to 8 days with an average of 5 days.