CLIMATE RESEARCH AND SERVICES INDIA METEOROLOGICAL DEPARTMENT MINISTRY OF EARTH SCIENCES PUNE Observed Rainfall Variability and Changes over Chhattisgarh State Met Monograph No.: ESSO/IMD/HS/Rainfall Variability/05(2020)/29 Pulak Guhathakurta, Usha Krishnan, Elizabeth Saji, Preetha Menon, Ashwini Kumar Prasad, Neha Sangwan and S C Advani GOVERNMENT OF INDIA MINISTRY OF EARTH SCIENCES INDIA METEOROLOGICAL DEPARTMENT Met Monograph No.: ESSO/IMD/HS/Rainfall Variability/05(2020)/29 Observed Rainfall Variability and Changes Over Chhattisgarh State Pulak Guhathakurta, Usha Krishnan, Elizabeth Saji, Preetha Menon, Ashwini Kumar Prasad, Neha Sangwan and S C Advani INDIA METEOROLOGICAL DEPARTMENT PUNE - 411005 1 DOCUMENT AND DATA CONTROL SHEET 1 Document Title Observed Rainfall Variability and Changes Over Chhattisgarh State 2 Issue No. ESSO/IMD/HS/Rainfall Variability/05(2020)/29 3 Issue Date January 2020 4 Security Unclassified Classification 5 Control Status Uncontrolled 6 Document Type Scientific Publication 7 No. of Pages 27 8 No. of Figures 42 9 No. of References 4 10 Distribution Unrestricted 11 Language English 12 Authors Pulak Guhathakurta, Usha Krishnan, Elizabeth Saji, Preetha Menon, Ashwini Kumar Prasad, Neha Sangwan and S C Advani 13 Originating Climate Research Division/ Climate Application & Division/ Group User Interface Group/ Hydrometeorology 14 Reviewing and Director General of Meteorology, India Approving Meteorological Department, New Delhi Authority 15 End users Central and State Ministries of Water resources, agriculture and civic bodies, Science and Technology, Disaster Management Agencies 16 Abstract India is in the tropical monsoon zone and receives plenty of rainfall as most of the annual rainfall during the monsoon season every year. However, the rainfall is having high temporal and spatial variability and due to the impact of climate changes there are significant changes in the mean rainfall pattern and their variability as well as in the intensity and frequencies of extreme rainfall events. The report brings the result of the analysis based on the recent 30 years of data (1989-2018) on the mean spatial rainfall pattern as well as mean spatial pattern of different rainfall events, trends and variability as well as extreme rainfall events during the monsoon months and annual for the state. 17 Key Words Rainfall trend, variability, extreme events, dry days 2 1. Introduction Chhattisgarh is located between 17°46’ N - 24°05’ N latitude and 80°15’ E- 84°20’ E longitude in Central India with Uttar Pradesh to the north, Jharkhand to the north- east, Orissa to the east, Telangana to the south, Maharashtra to the south-west and Madhya Pradesh to the north and north-west form its boundaries. The State of Chhattisgarh has geographical area about 135,194 sq km. About 44% of its total area is covered by forests. Physiographically the state is divided into three parts viz. Northern Hill Ranges, Chhattisgarh Plain and Bastar Plateau. Chhattisgarh Plains: This belt comprises of central area of the state. About 33% of its total geographical area of the plain is covered with forest. Bastar Plateau: This belt comprises of almost southern part of the state covering Bastar, Bijapur, Dantewada, Kanker, Kondagaon, Narayanpur and Sukma districts. In this plateau, the land is undulating hills where peak height is about 1144 metre above mean sea level. The forest area in this plateau contributes 62% of the total geographical area. Northern Hills: This belt comprises of almost northern portion of the state covering Balrampur, Jashpur, Koriya, Surajpur, Surguja and some part of Bilaspur, Korba, Mungeli and Raigarh districts. The forest area in this belt is about 47% of the total geographical area of this hilly region. Already there are many studies available on the observed trends and variability of rainfall and also extreme rainfall events over India, but all the studies are based on past 100 years or more data and also the recent years are not included (Nema et al, 2018; Guhathakurta et al, 2015; Guhathakurta et al, 2011; Guhathakurta&Rajeevan, 2008 etc). Also there are limited studies on district rainfall trends and variability. In the present report all the analysis of observed rainfall patterns, trends and variability have been done based on recent past 30 years (1989-2018) that will help to have idea of the recent changes for climate change adaptation and management by the state authorities. 2. Data and Methodology Daily Rainfall data from 1989 to 2018 is considered for analysis of trend variability and mean rainfall patterns. From the daily rainfall data monthly rainfall series of each stations are computed and then monthly district rainfall series has been constructed by considering arithmetic average of all the station rainfall values within the district. The monthly rainfall series of the state has been computed by using area weighted rainfall values of all the districts within the state. The objective of the analysis is to: 1. Identify the spatial pattern of the mean rainfall 3 2. Understand district wise observed rainfall trend and variability in annual and SW monsoon season (June, July, august and September). 3. To identify the spatial pattern of intensities of various rainfall events and dry days and also trends if any in the intensity of various rainfall events and also number of dry days. The analysis has been done in two parts. For identification of the spatial pattern, mean rainfall and variability and observed trends, we have used district rainfall series and results have been brought out for four southwest monsoon months viz. June, July, August, September, for the southwest monsoon season and for annual. Fig.1 gives the location of the districts of the state. For identification of mean pattern and also trends of intensities of various rainfall events we used the station daily rainfall data. From the mean and standard deviation, coefficient of variation (CV) is calculated as follows: Standard Deviation Coeffcient of variation (CV) = × 100 Mean Fig. 1 Location of the districts of Chhattisgarh 4 3. State rainfall mean and variability and trend Table 1 shows the mean rainfall (mm) and coefficient of variation of the state for the monsoon months, southwest monsoon season and annual during the period 1989-2018. It can be seen that the state gets highest rainfall (33% ) of south west monsoon rainfall in July month while the August month gets 31% of the south west monsoon rainfall). June and September receive 17% and 19% of south west monsoon rainfall respectively. Also approximately 90% of annual rainfall is received during the southwest monsoon season only. The variability of monsoon and annual rainfall is also very less (15%). June July August September JJAS Annual Mean 185.8 373.4 353.1 211.7 1124.0 1249.9 CV 39.6 25.4 19.1 35.4 15.3 15.4 Table 1 Mean rainfall (mm) and coefficient of variation of the state for the monsoon months, southwest monsoon season and annual Fig. 2 and 3 show the time series of rainfall in mm for the months of June, July, August, September and southwest monsoon season and annual respectively. The trend lines are also displayed for each of the series. Neither monthly rainfall nor seasonal or annual rainfall show any significant increasing/decreasing trend. In the monthly rainfall September rainfall shows increasing trend while June, July and August rainfall show decreasing trend. Both seasonal and annual rainfall show decreasing trend. During the last 30 years highest rainfall of June and July received in the year 1994 (390.8 mm and 593.2 mm respectively) while the highest rainfall of 506.0 in August and of 370.2 mm in September received in the year 2003. Highest annual rainfall of 1748.3 mm and highest southwest monsoon rainfall of 1643.1 mm received in the year 1994. Lowest rainfall for June, July, August, September, SW monsoon season and annual was 47.4 mm (Year 2009), 136.5mm (Year 2002), 218.1mm (Year 2000), 101.9 mm (Year 2001), 826.4 mm (Year 2002) and 883.9 mm (Year 2000) respectively. 5 Fig. 2 Time series of rainfall in mm for the months of June, July, August, September and trends Fig. 3 Time series of rainfall in mm for the southwest monsoon season and annual trends 6 4. District rainfall mean, variability and trend 4.1 Mean and coefficient of variation Table 2 gives the rainfall statistics for the districts of Chhattisgarh for the four monsoon months, southwest monsoon season and annual while Fig. 4-5 shows the spatial pattern of these statistics. It can be seen that the district of Dantewara received highest rainfall during all the months and season(1450mm in SW monsoon). Rainfall received over this district is around 210-230 mm in June, 440-480 mm in July, 470-530 mm in August, 255-290 mm in September and during the SW monsoon and annual 1300-1730 mm. Lowest rainfall received during the SW monsoon season and annual is over Kowardha district (792 mm and 926 mm respectively) JUNE JULY AUGUST SEPTEMBER MONSOON ANNUAL DISTRICT MEAN CV MEAN CV MEAN CV MEAN CV MEAN CV MEAN CV BASTAR 211.5 50 382.6 33 399.3 34 245.2 46 1238.6 22 1450.5 38 BILASPUR 170.8 46 307.7 31 303.8 22 189.4 50 971.6 18 1110.2 39 DANTEWARA 230.8 71 481.2 94 526.9 53 255.9 105 1494.9 64 1677.3 80 DHAMTARI 186.6 174 368.2 102 335.6 108 207.4 188 1097.9 69 1231.3 77 DURG 175.3 132 368.0 83 305.2 86 180.0 131 1028.5 55 1134.0 73 JANJGIR 173.2 147 381.1 98 343.5 103 200.5 192 1098.3 63 1191.6 67 JASHPURNAGAR 230.2 51 407.2 29 328.2 27 248.3 46 1213.9 22 1378.2 39 KANKER 185.0 206 447.5 108 456.0 103 214.6 220 1303.0