VOL. IX, ISSUE XXXI, OCT 2019 MULTILOGIC IN SCIENCE ISSN 2277-7601 An International Refereed, Peer Reviewed & Indexed Quarterly Journal in Science, Agriculture & Engineering. EXPLORING RAINFALL VARIABILITY AND DROUGHT (USING SPI) FOR WESTERN AGRO CLIMATIC ZONE OF Kokilavani Sembanan1 1Assistant Professor, Agro Climate Research Centre, Tamil Nadu Agricultural University, (Received: 22.08.2019; Revised: 03.10.2019; Accepted: 04.10.2019) (RESEARCH PAPER IN AGRO CLIMATE RESEARCH) Abstract Drought is a normal, recurrent feature of climate and is observed in all the climatic zones. However, it has significantly different characteristics from one region to another. The rainfall data over a period of 30 years (1981-2010) for different point locations of Coimbatore and were collected from Agro Climate Research Centre, Tamil Nadu Agricultural University, Coimbatore and Agricultural Research Station, . Further to understand the drought climatology of southern zone of Tamil Nadu, Standardized Precipitation Index (SPI) was used. The SPI programme developed by National Drought Mitigation Centre of University of Nebraska was utilized to compute SPI. The rainfall analysis revealed that Sulur and Coimbatore exhibited low dependability of southwest monsoon rainfall by recording 55 and 52 per cent of co-efficient of variation respectively. Besides Bhavani, the annual rainfall recorded in all the locations was highly dependable which was indicated by the recorded lowest values of Co-efficient of Variation. During southwest monsoon, Bhavani and Perundurai points recorded highest CV of 50 and 52 per cent respectively which indicated low dependability of rainfall. During Northeast monsoon, all the point locations at Coimbatore an Erode recorded the highest dependable rainfall. SPI analysis indicated on annual basis, , Sulur and Coimbatore recorded the extreme drought category at Coimbatore while at Erode, Bhavani recorded the maximum event of occurrence (3) for extreme drought category. Keywords: Rainfall, Co-efficient of Variation, SPI, drought Introduction is a key variable to study meteorological drought. Among the Rainfall is an unique variable, which reflects multiple factors meteorological indices, Standardized Precipitation Index (SPI) is locally and globally. The distribution of rainfall depends upon more commonly used. The SPI has certain advantages over others various factors existing at regional scale. It is being a single most such as use of rainfall data alone and also its variable time scale, important factor for success of crops in the farming areas. which allows it to describe drought conditions important for a range Venkatraman et al., (2013) studied the rainfall variability in of meteorological, hydrological and agricultural applications (McKee district and reveal the variation in the trends. The rainfall distribution et al., 1993). and trend for Salem district were analyzed in by Gurugnanam et al., Materials and Methods (2010), and shown the variation with the amount of precipitation in The rainfall data over a period of 30 years (1981-2010) for different the particular domain. Moreover, factors like climate change and point locations of Coimbatore and Erode were collected from Agro urbanization have also had an impact on the variation in rainfall. Climate Research Centre, Tamil Nadu Agricultural University, Recent studies have stated that any analysis of hydro-climatic Coimbatore and Agricultural Research Station, Bhavanisagar. variables should be done at the local scale rather than at a large or Meteorological Department (IMD) gridded data was used for the non- global scale. availability of the point data. The mean rainfall for the point location Drought incidences, regardless its severity, have become more and co-efficient of variation (CV) were analysed to study the common in recent years in parallel to global climate changes. dependability of rainfall as given by Veeraputhiran et al., 2003. Droughts have adverse socioeconomic, agricultural, and The SPI programme developed by National Drought Mitigation environmental impacts that can be reduced by assessing and Centre of University of Nebraska was utilized to compute SPI and the forecasting drought behaviour. Drought indices are one of the very criteria defined by McKee et al.(1993) for a “drought event” was important tools to monitor and to assess drought, because they considered to classify the drought intensities for any time steps used simplify complex inter-relationships between many climate for interpretation. A drought event occurs if the SPI value is -1.0 or parameters. There is extensive literature on the quantification of less and the event ends when the index becomes positive. The drought by using various indices, models and water balance different timescale helps to identify the types of drought from simulations. meteorological to hydrological drought (Adnan et.al., 2015). Precipitation has been used to develop a variety of indices, because it Table.1 Classification of Standard Precipitation Index values and rainfall of 1849.7 mm followed by Pollachi Taluk which received their intensities 821.1mm (Table 2). The Northern tip of Coimbatore (mettupalayam) SPI Intensity recorded 734.6 mm which was followed by Coimbatore North(650.9 mm). The rainfall pattern gradually reduced towards the east side of 2.00 and more Extremely wet Coimbaotore (sulur) which recorded 576.7 mm of rainfall. All 1.99 to 1.50 Very wet locations showed higher dependability of annual rainfall at 1.49 to 1.00 Moderate wet Coimbatore. -0.99 to 0.99 Near normal Huge amount of rainfall variation was noticed during southwest monsoon. Half of the northern part of district received low rain and -1.00 to -1.49 Moderate drought half of southern part received heavy rainfall during this season. Most -1.50 to -1.99 Severe drought of south and west of Pollchi and Palaghat gap experienced highest -2.00 and less Extremely drought rainfall, because of the influence by leeward in . Sulur and Coimbatore exhibited low dependability of southwest monsoon Results and Discussion rainfall by recording 55 and 52 per cent of co-efficient of variation Rainfall analysis for Coimbatore respectively. For Coimbatore, among the different blocks studied, on annual basis, During Northeast monsoon, highest rainfall was observed at the southern edge of Coimbatore () recorded the highest Valparai(488.2mm) and the lowest rainfall recorded at Pollachi VOL. IX, ISSUE XXXI, OCT 2019 MULTILOGIC IN SCIENCE ISSN 2277-7601 An International Refereed, Peer Reviewed & Indexed Quarterly Journal in Science, Agriculture & Engineering. (298.9). All locations showed high dependability of northeast was indicated by the recorded lowest values of co-efficient of monsoon rainfall at Coimbatore. variation. Rainfall analysis for Erode During southwest monsoon, bhavani and perundurai point recorded For Erode, among the different blocks studied, on annual basis, Erode highest CV of 50 and 52 per cent respectively which indicated low recorded higher rainfall (745 mm) and Bhavani recorded the lowest dependability of rainfall. The remaining point locations recorded the annual rainfall (634 mm)(Table 3). Besides Bhavani, the annual lowest CV which inferred high dependability of rainfall. For the rainfall recorded in all the locations was highly dependable which Northeast monsoon, all the points recorded the lowest CV values and showed high dependability of rainfall. Table 2.Rainfall statistics for different points of Coimbatore LOCATION SWM NEM Annual RF(mm) CV(%) RF(mm) CV(%) RF(mm) CV(%) Coimbatore 190.3 52 321.8 25 650.9 24 Mettupalayam 152.7 48 379.8 22 736.4 21 Pollachi 369.2 22 298.9 18 821.1 25 Sulur 105.6 55 326.6 21 576.7 22 Valparai 1082.8 12 488.2 11 1849.7 19 Table 3.Rainfall statistics for different points of Erode LOCATION SWM NEM Annual RF(mm) CV (%) RF(mm) CV (%) RF(mm) CV (%) Erode 315 38 336 11 745 20 328 48 305 28 722 19 Perundurai 220 52 315 25 645 23 Bhavani 207 60 302 37 634 28 Sathyamangalam 259 32 337 15 736 22 SPI analysis for Coimbatore of events (2) at Mettupalayam while no event of occurrence recorded SPI analysis showed that moderate drought intensity (-1.0 to -1.49) at Valparai during Southwest monsoon. All the point data recorded had maximum event of occurrence (4) during Southwest monsoon at minimum event of occurrence (1) during Northeast monsoon. On Coimbatore and Mettupalayam points while no event of occurrence annual basis, Mettupalayam and Sulur recorded maximum number of recorded at Valparai (Table 4). During Northeast monsoon, events (2) and no event occurred in the remaining points of location. Coimbatore and Pollachi recorded more number of events (4) and The Extreme drought intensity (>-2.0) was recorded at Coimbatore minimum event of occurrence (2) at Valparai. On annual basis, town and Sulur during Southwest monsoon period. No event of Coimbatore town had maximum occurrence (5) and no event extreme drought occurrence was observed during northeast monsoon recorded at Valparai. period. On annual basis, Pollachi, Sulur and Coimbatore recorded the The severe drought intensity (-1.5 to -1.99) had its maximum number extreme drought category. Table 4.Drought intensity and frequency for different points of Coimbatore using SPI Season/Points Coimbatore town Mettupalayam Pollachi Sulur Valparai Moderate(-1.0 to -1.49) SWM 4 4 3 3 0 NEM 4 3 4 3 2 Annual 5 4 2 4 0 Severe(-1.5 to -1.99) SWM 1 2 0 1 0 NEM 1 1 1 1 1 Annual 0 2 0 2 0 Extreme(-2.0 and less) SWM 1 0 0 1 0 NEM 0 0 0 0 0 Annual 1 0 2 2 0 SPI analysis for Erode number of events (3) of severe drought category. On annual basis, SPI analysis showed that moderate drought had maximum event of Perundurai recorded the maximum event of occurrence (3) for the occurrence (4) at Perundurai and minimum event of occurrence at severe drought category Gobichettipalayam during southwest monsoon(Table 5). During Extreme drought event had its maximum occurrence (2) at Gobi and Northeast monsoon, maximum event of occurrence (5) recorded at Bhavani during southwest monsoon. During Northeast monsoon, no Perundurai and minimum event of occurrence at Bhavani. On annual event of extreme drought category occurred for different points of basis, Perundurai recorded the maximum event of occurrence (4) for Erode. On annual basis, Bhavani recorded the maximum event of the moderate drought category. occurrence (3) for extreme drought category. A similar finding of no The severe drought category had its maximum number of events (3) event of extreme drought occurrence for southern agro climatic zone at Gobichettipalayam, Perundurai and Bhavani during southwest of Tamil Nadu was observed by Ramaraj et al., 2015. monsoon. During Northeast monsoon, Bhavani had its maximum Table 5.Drought intensity and frequency for different points of Erode using SPI Season/Points Erode Gobichettipalayam Perundurai Bhavani Sathyamangalam Moderate(-1.0 to -1.49) SWM 2 1 4 2 2

www.ycjournal.net NAAS Rating- 5.20 Impact factor-4.035 159 VOL. IX, ISSUE XXXI, OCT 2019 MULTILOGIC IN SCIENCE ISSN 2277-7601 An International Refereed, Peer Reviewed & Indexed Quarterly Journal in Science, Agriculture & Engineering. NEM 3 3 5 1 3 Annual 0 1 4 0 2 Severe(-1.5 to -1.99) SWM 1 3 3 3 2 NEM 1 0 1 3 0 Annual 2 2 3 2 2 Extreme(-2.0 and less) SWM 1 2 1 2 0 NEM 0 0 0 0 0 Annual 0 1 2 3 0 Conclusion Rainfall is the major source of water for agriculture and the spatial and temporal uneven distribution of rainfall leads to occurrence of flood and drought in different regions simultaneously. The rainfall analysis revealed that Sulur and Coimbatore exhibited low dependability of southwest monsoon rainfall by recording 55 and 52 per cent of co-efficient of variation respectively. Besides Bhavani, the annual rainfall recorded in all the locations was highly dependable which was indicated by the recorded lowest values of Co-efficient of Variation. During southwest monsoon, Bhavani and Perundurai points recorded highest CV of 50 and 52 per cent respectively which indicated low dependability of rainfall. During Northeast monsoon, all the point locations at Coimbatore an Erode recorded the highest dependable rainfall. SPI analysis indicated on annual basis, Pollachi, Sulur and Coimbatore recorded the extreme drought category at Coimbatore while at Erode, Bhavani recorded the maximum event of occurrence (3) for extreme drought category. References Adnan S., Ullah K. and Gao S 2015. Characterization of drought and its assessment over Sindh, Pakistan during 1951–2010. J Meteorol. Res., 29(5): 837-857. Gurugnanam, .B Suresh M, Vinoth M and Kumaravel S. 2010. High/Low Rainfall Domain Demarcation Mapping Using GIS at Salem District, Central Tamil Nadu. (ISSN 0974 - 6846). Ind J Sci and Technol., 3(5): 542-545. McKee T. B., Doesken N. J. and Kleist J. 1993.The Relationship of Drought Frequency and Duration to Time Scales, Proceeding of the Eight Conference on Applied Climatology 17-22 January, Anaheim, California. Ramaraj A.P, Kokilavani, S Manikandan, N Arthirani, B and. Rajalakshmi D. 2015. Rainfall Stability and Drought Valuation (Using SPI) Over Southern Zone of Tamil Nadu. Curr. Wor. Envt., 10(3): 928-933 Veeraputhiran R, Karthikeyan R, Geethalakshmi V, Selvaraju R., Sundarsingh S. D, Balasubramaniyan T. N. 2003. Crop planning – Climate Atlas, Manual”, A. E. publications, Coimbatore – 41 Venkat Raman A.T.V.R, Gurugnanam B, Arunkumar. M. 2013. One decade hydro meteorological data assessment through statistics, Dindigul district, Tamil Nadu, (ISSN 0976 – 4380), 3: 659- 667.

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