Analysis of Rainfall Pattern -A study in Agro-climatic Zones in Dry region in Karnataka state

1. Introduction

     The emission of green house gases disturbs the established energy balance of the atmosphere which result in rising temperature and increased erraticity of climatic parameters. The global annual mean surface temperature has increased by more than 1.5°C above the pre -industrial level^[1]. This increase in temperature has caused unprecedented changes across the human and natural systems. In the process of gradual warming, the mean temperature shifted upward which amounts to climate change. In India, the last five decades experienced an increase in the frequency and magnitude of extreme rain events over central India, western India, north-eastern India, and southern India whereas, an increase in the frequency of severe droughts have been observed over south India, central Maharashtra, the Indo-Gangetic plains, north and northwest India^[2]. The vulnerability of a system is determined by concepts of exposure, sensitivity and adaptive capacity towards climate change.

       Semi-arid regions of peninsular India are vulnerable to drought and water stress due to the uneven distribution of monsoon rainfall. The delay in monsoon or dry spells adds pressure on available water resources. Even in such situations farmers in semi-arid India continue to grow water intensive crops. Karnataka ranks second among drought affected states after Rajasthan with frequent occurrence of droughts once in five years. The impact of climate shock creates unequal access to resources, food insecurity and incidence of poverty in the country. The risk associated with climate change calls for a broad spectrum of policy responses and strategies at the local, regional, national and global level to mitigate the effect of the same. Karnataka has a Dry zone, Transition zone and Hilly zone which further divided into 10 agro climatic zones. The dry zone has five agro climatic zones which covers a large area in the state  namely North Eastern Dry Zone ,Northern Dry Zone , Central Dry Zone,  Eastern Dry Zone and Southern  Dry Zone . The rainfall dispersion has more effect on crop productivity especially the crops which required more irrigation. The analysis of rainfall pattern will help the policy makers and researchers to develop new varieties which withhold the drought severity. Therefore, the study attempted to examine the magnitude of drought in dry agro climatic zone of Karnataka.

2.  Methodology                                                                                                                      

 Karnataka is located between 11° 40′ N and 18° 27′ N latitudes and between 74° 5′ E and 78° 33′ E longitudes, at the center of the western Peninsular India covering an area of 19.1 million hectares, accounting for 5.8 % of the country’s total geographical area .The northern dry zone   has 5.04 Million ha which is large in area and also receives an average rainfall of 500 to 625 mm among other zones as shown in Table 1.

Table 1: Physiographic of Agro climatic zones in Dry region in Karnataka

Source: Department of Mines and Geology, Government of Karnataka Annual Report 2013

The lowest rainfall was received by CDZ with 400 to 620 mm. The highest rainfall was received by EDZ with 750 to 810 mm. Rainfall measure is used in drought index calculations as it is the most vital hydrological variable generally the only meteorological measurement made in semi arid areas^[3]. Climatic variables like daily rainfall, temperature from 1979 to 2019 across Karnataka state was collected from AICRPAM CRIDA, Hyderabad.

North Eastern Dry Zone	Northern Dry Zone
Central Dry Zone	Eastern Dry Zone
Southern Dry Zone

Map 1: Different Agro-Climatic Zones of Dry Region in Karnataka State

i) Rainfall Anomaly Index (RAI)

In this study,  RAI is modified to account for non normality like  Standard precipitation Index (SPI) is used for the assessment of both temporal and spatial droughts as it is independent of time and space. Hence it is more useful in semi-arid regions particularly like India, as at many meteorological stations the recorded rainfall data available is less than 30 years, while most of the metrological drought assessment indices require more than 30 years of data^[4]. RAI is used to assess and identify droughts, drought severity and variability by comparing with some established arbitrary value. It is described as rainfall variability over a time and is estimated as below:

For positive anomalities

                                                            RAI= ………….(1)

 For negative anomalities

                                                          RAI = ………….(2)    

                        Where,    RNF = Actual rainfall for a given year (mm)

                                       RNF_m =Mean rainfall of the total length of record (mm)

                                             X= Mean of the ten highest values of rainfall (mm)

      Y= Mean of the ten lowest values of rainfall (mm)

Table 2: Classification of Rainfall Anomaly Index 

( Source: Keyantash and Dracup,2002)

A ranking of nine classes of rainfall abnormality ranging from extremely wet to extremely dry and range of each class^[5] is shown in Table 2 . If the purpose of the study is to investigate dry periods the negative prefixed RAI is used, while positive RAI is used to study wet periods^[6].

ii)  Percentage of Deficit rainfall (DR) or Rainfall Surplus (RS)

 The percentage annual rainfall departure from the long term mean annual rainfall was used for drought assessment ^[7] for all the stations. Percent of deviation for each year was further categorized into four percentage ranges namely 0 to 10, 10 to 15, 15 to 20 and greater  than 20.

Percentage of Deviation= (P_act –P)/P *100

P_act –Precipitation of the region

P-Mean precipitation of the region

* AR –Annual Rainfall; MD-Mean deviation ;RAI-Rainfall Anomaly Index; DR- Deficit Rainfall; SR-surplus Rainfall                 

3. Results and Discussion

3.1 Analysis of  Dry and Wet years in North Eastern Dry Zone

 In North Eastern Dry Zone, the dry years occurred for 21 years.  Extreme drought occurred in 2018 and 2015 (RAI  < -3). The severe drought condition occurred for eight years i.e. 2019, 2003, 2006, 1994, 2016, 2004, 2002 and 1980 as the RAI values ranges from -2.1 to -3 as shown in Table 3. For seven years the zone recorded an RAI between  -1.192 to -1.11 which imply  medium drought situation experienced by the zone. The majority of the year falls in the normal  and weak  wet category. The extreme wet year with RAI > 3 occurred between during 1998 and 2005.  NEDZ has maximum  mean deviation (MD)  in the year 2018 with MD value –249.23mm with -50.52 % DR. The minimum MD occurred in the year 1984  with value -18.57 mm  which also recorded -3.69 % deficit rainfall (DR).The maximum wet year was observed in the year 1998  with a positive deviation of 246.29 mm with 48.90 % SR. The minimum wet year was observed in the year 1993  with positive deviation of 3.90 mm with 0.77% SR.

Table 3: Rainfall Pattern in North Eastern Dry  Zone

3.2 Analysis of  Dry and wet years in Northern Dry  zone

In Northern Dry  Zone, the dry years occurred for 23 years (57.5 %) out of the 40 years of study period.  Extreme drought conditions were observed during the years 2003, 1983, 1984, 2001 and 1985 and recorded the Rainfall anomaly index  value of less than minus three (< -3 RAI). The severe drought condition occurred for six years  i.e. 1997, 2002, 2016, 1996, 1994 and 2000 and recorded the rainfall anomaly index in the range -2.1 to -3 (Table 4).The normal drought condition prevailed in nine years and recorded the RAI value from  -1.87 to -1.00. The Majority of the study period falls in the normal and moderate wet categories. The extreme wet years was observed in the years 2014, 2008, 2010 and 2009 with an estimated rainfall anomaly index value of more than three (RAI> 3). NDZ has experienced maximum mean deviation in rainfall (-137.14 mm) in the year 2003 recording deficit rainfall of -38.82%. The year 1981 recoded the least  amount of mean deviation in rainfall (-11.57 mm) and experienced deficit rainfall of just -3.28 %. The year 2014 was the topmost in the category of maximum wet year experiencing a positive deviation of  204. 27 mm and with surplus rainfall of 57.81  %. The year 1988 ranks lowest among the category of wet years with an estimated positive deviation of 1.68  mm and with surplus rainfall of 0.48  %.

Table 4: Rainfall Pattern in Northern Dry  Zone

3.3 Analysis of  Dry and wet years in Central  Dry  zone

In Central Dry Zone, the dry years occurred for 23 years accounting for 57.5 per cent of the study period of 1979-2019.  Extreme drought was experienced in four years i.e., 1985, 2003, 1995 and 2016  and the estimated rainfall anomaly index was less than minus three (RAI < -3). Severe drought conditions were observed to prevail in four  years i.e., 2002, 1990 ,1984, and 1989  recording the  RAI values ranging between -2.1  to -3 (Table 5). The zone suffered from medium drought for  seven years which is revealed from the estimated RAI value ranging from  -1.84  to -1.00. The majority of the years falls in the medium and severe   wet category. The extreme wet year with an estimated rainfall anomaly index value of more than three  (RAI > 3) was in years,  2010, 2015, 2019, 2005 and 2014. In CDZ the  maximum mean deviation in rainfall was observed to have happened in the year 1985  (MD value –230.50.mm) and the deficit rainfall was -43.05%. The minimum mean deviation in rainfall occurred in the year 1993  with a value -3.90 mm, and was associated with deficit rainfall of -0.73  percent .The  wet year was observed to have occurred in  2010  with mean maximum deviation in rainfall of 305.20 mm and with surplus rainfall of 57.00 %.  The minimum wet year was in the year  1979  with the minimum  deviation in rainfall  being  17.30 mm which was associated with surplus rainfall of   3.23 %.

Table 5: Rainfall Pattern in Central Dry  zone

3.4 Analysis of  Dry and wet years in Eastern Dry  Zone

  In Eastern Dry Zone, the dry years occurred for 23 years (Table 6). Extreme drought (RAI <-3) occurred in 2002, 2003, 1985, 1982 and 2018. The severe drought condition occurred for four years i.e. 1990, 2006, 1980 and 2016 as the RAI values ranges -2.1 to -3 as shown in Table 4.40. In six  years the RAI value was recorded to be between -1.19 to -1.05  implying occurrence of medium drought  in the zone. The majority of the years falls in the normal  and weak wet category. The extreme wet year with RAI > 3 occurred in 2005, 2015, 2017 and 1991.  EDZ has maximum mean rainfall deviation (MD) in the year 2002 with MD value -413.00 mm with deficit rainfall (DR) of -42.41 % . The minimum MD occurred in the year 1997  with value -7.8  mm  recording a deficit rainfall of -0.80 %.The maximum wet year is 2005 with a positive deviation of 577.55 mm with 59.31 % SR. The minimum wet year is 2004 with a positive deviation of 4.98 mm with 0.51% SR.

Table 6: Rainfall Pattern in Eastern Dry  Zone

3.5 Analysis of  Dry and Wet years in Southern Dry  zone

 In Southern dry Zone, the dry years occurred for 20 years as shown in Table 7.  Extreme drought occurred in 2003, 2002, 1985, 2001, 2016 and 1990 ( < -3 RAI) . The severe drought condition occurred in 1982 and 2012. About five years were  recorded with RAI from -1.88 to -1.38   which implies as normal drought  in the zone. The majority of the years falls in weak and moderate wet categories. The extreme wet years with RAI > 3 occurred in 2005, 2008, 2017 and 1981. SDZ has maximum mean deviation in the year 2003  with MD  value -348.40 .mm with -38.07% DR. The minimum MD occurred in the year 1993  with value -0.42  mm which also recorded with -0.05  % DR .The maximum wet year is 2005   with a positive deviation of  503.79 mm with 55.06  % SR. The minimum wet year is 1987 with a positive deviation of 1.31  mm with 0.14  % SR.

Table 7: Rainfall Pattern in Southern Dry  zone

 Conclusion and policy implication

The assessment of rainfall occurrence and dispersion is essential to estimate the irrigation supply to farm & nonfarm population for domestic and farm use respectively. The study revealed that, there is difference in drought occurrence and its intensity across the agro-climatic zones in dry regions. Out of five dry zones, three are recorded with  23 years of drought which effects the Kharif crop production . Therefore, Investment should be made in the creation of micro irrigation methods, water harvesting structures like check dams and farm ponds which helps the farmers to increase crop production despite of existing drought condition in state.

Acknowledgments

This paper is a part of the Ph.D. research work of the author. The authors are thankful to ICAR-IARI for their financial assistance to carry out the research work and extend their gratitude to SAU-ANGRAU  for granting study leave.

Competing Interests

The Author has  declared  that  no  competing  interests exists.

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