Drought is one of the complex natural phenomena. In extreme cases, drought causes great damage to the economy and human life. The economic loss caused by drought is high compared to all other weather disasters. (Wilhite, 2000). Globally, drought causes an economic loss at an average of 6 to 8 billion USD (Yagci et al., 2013). Drought is one of the least mention natural calamity (Kao and Govindaraju, 2010). Droughts can be classified as agricultural, hydrological, meteorological and socio-economic droughts (Shiau et al., 2012). The climatic parameters such as rainfall and temperature play a crucial role in defining drought. Among the climatic parameters rainfall is an important factor and is a readily available weather measurement. Using rainfall data from thirty or more years is better for effective growth planning than using short-term ones (Dennett et al., 1985). It also affects agriculture, drainage, human settlements and politically and its impact varies from place to place.

The Nambiyar basin covers a part of Tirunelveli, Thoothukudi and Kanyakumari districts of Tamil Nadu. Geographically,the basin extends between 08° 08’00”N to 08° 33’ 00”N latitude and 77° 28’00”E to 78° 15’ 00”E longitude. The basin is surrounded by Tamiraparani basin on and Kodaiyar basin on north and southern side respectively. Eastern part of the basin is covered by Gulf of Mannar and the western part is by Kerala state. The total area of the basin is 2018.4 sq.km. Karamaniyar river in northern side, Hanumanadhi river in the southern part and the Nambiyar river lies in between these two rivers are the major rivers draining this basin. The maximum and minimum temperature of the basin is 33^oC and 28^oC respectively. The Nambiyar river originates in the eastern slopes of Western Ghats exactly over Nalikkal Mottai located 9.6 km west of Thirukkarangudi village. Millets, pulses, oil seeds, coconut and fewer area is under paddy cultivation are some of the major cops of the basin (Figure 1 ).

The base map of Nambiyar river basin was digitized from river basin map of Tamil Nadu. The in and around rainfall data for Nambiyar basin from the year 1981 to 2017 were used in this study to understand the drought. The basin covers 13 gridded points collected from ECMWF reanalysis Interim (ERA-1) data set having horizontal resolution of 0.75⁰. This gridded data were downscaled to 17X17 km resolutions using WRF re-initialization method were adopted. The gridded points are considered as rainfall location such as, Valliure, Elankulam, Sirappur, Chidambarapuram, Vadakankulam, Nainaputhoor, Boothapandi, Keeriparai, Manjolai, Venkatarngapuram, Nellaiyappapuram, Veppenkulam and Ammanpuram. The graphs were prepared using Excel software and spatial maps were prepared using Arc GIS platform.

The Meteorological Department of India and the National Agriculture Authority provide the percentage of normal rainfall and associated weather drought intensity rainfall departures (Table 1). During this study period, the study area is comes under two categories such as moderate and mild drought. Most of the location in this study area is under mild drought. The stations which having maximum number of years fall under moderate drought is Vallioor, followed by the stations are Veppankulam, Elankulam, Sirappur, Vadakkankulam, Venkatarengapuram, Nellaiyappapuram, Manjolai and Ammanpuram. Minimum drought years are noted in Chidambarapuram, Nainaputhoor and Boothapandi stations during the study period (Figure 2). Chidambarapuram and Nainaputhoor are the location have high number of years with mild droughts and minimum year are found in Elankulam station followed by Boothapandi, Keeriparai, Manjolai, Venkatarengapuram and Nellaiyappapuram station (Table 2).

Spatially, the moderate droughts years found above three years are noted in western part, north eastern part of the study area and below 3 drought years found in central and southeastern part of the basin. Northern, central and southeastern part of the study area have maximum number of mild drought category ie., above 20 years and below 20 years were found in western and northeastern part. The years which having greater than 15 years of no droughts was observed in western and eastern part of the study area. Below 15 drought years found in central part of study period (Figure 3)

The main aim of the study is to analyze the drought character using DI and RAI index. The results obtained in this study give almost identical results while comparing the drought years. The two drought index reveals more or less similar results in the drought years. The common drought years between two indexes are notes as 1986, 2003, 2013 and 2016 during the study period. So, both the index is useful for to identify the drought condition in the study area. Even though, the study area is not affected by severe and extreme drought but the recent years indicates most of the stations are under moderate drought conditions. It shows that the basin slowly experiencing drought conditions. So, proper drought management plan is required to mitigate before it goes extreme conditions.

I greatly acknowledge ICSSR for providing grant to carry out research work and I also thank department of geography for giving space to carry out research.