Karnataka State
Total Page:16
File Type:pdf, Size:1020Kb
CLIMATE RESEARCH AND SERVICES INDIA METEOROLOGICAL DEPARTMENT MINISTRY OF EARTH SCIENCES PUNE Observed Rainfall Variability and Changes over Karnataka State Met Monograph No.: ESSO/IMD/HS/Rainfall Variability/13(2020)/37 Pulak Guhathakurta, Sakharam Sanap, Preetha Menon, Ashwini Kumar Prasad, S T Sable and S C Advani GOVERNMENT OF INDIA MINISTRY OF EARTH SCIENCES INDIA METEOROLOGICAL DEPARTMENT Met Monograph No.: ESSO/IMD/HS/Rainfall Variability/13(2020)/37 Observed Rainfall Variability and Changes Over Karnataka State Pulak Guhathakurta, Sakharam Sanap, Preetha Menon, Ashwini Kumar Prasad , S.T. Sable and S C Advani MMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMM MMMM INDIA METEOROLOGICAL DEPARTMENT PUNE - 411005 1 DOCUMENT AND DATA CONTROL SHEET 1 Document Title Observed Rainfall Variability and Changes Over Karnataka State 2 Issue No. ESSO/IMD/HS/Rainfall Variability/13(2020)/37 3 Issue Date January 2020 4 Security Unclassified Classification 5 Control Status Uncontrolled 6 Document Type Scientific Publication 7 No. of Pages 23 8 No. of Figures 42 9 No. of References 3 10 Distribution Unrestricted 11 Language English 12 Authors Pulak Guhathakurta, Sakharam Sanap, Preetha Menon, Ashwini Kumar Prasad, S.T. Sable and S C Advani 13 Originating Division/ Climate Research Division/ Climate Application Group & User Interface Group/ Hydrometeorology 14 Reviewing and Director General of Meteorology, India Approving Authority Meteorological Department, New Delhi 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 The State of Karnataka, confined roughly within 11.5°N and 18.5°N 1atitudes and 74°E and 78.5°E longitude, is situated on a table land in the angle where the Western and Eastern Ghat ranges converge into the Nilgiri hill complex. It is therefore, enclosed by chains of mountains to its west, east and south. The state consists mainly of plateau which has a higher elevation of 600 to 900 m. a. s. l. in the southern half and 300 to 600 m.a.s.l. in the north. Almost the entire lands cape is undulating, broken up by mountains and deep ravines. Plain land of elevation less than 300 m. a. s. l. is to be found only in the narrow coastal belt of the State facing the Arabian Sea. This coastal belt with an average width of 50 to 80 km. covers a distance of about 225 km. from north to south. There are quite a few high peaks both in western and Eastern Ghat systems with altitude more than 1500 m. Mulaingiri situated in Bababudan range of the Western Ghats is the highest point with an altitude of 1914 m.(6317 ft). The district wise mapof the state is presented in Fig. 1. The climate of the State is considerably influenced by its orographic features. Three important river systems traverse across the State, namely, Krishna in the north, Cauvery in the south and Tungabhadra in the central part. Many studies are available on the observed trends and variability of rainfall and also extreme rainfall events, but all the studies are based on past 100 years or more data and also the recent years are not included (Guhathakurta et al, 2015; Guhathakurta et al, 2011; Guhathakurta & Rajeevan, 2008 etc). Also there are limited studies on Karnataka state rainfall analysis. 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. 3 Fig. 1 Location of the districts of Karnataka 2. Data and Methodology Daily Rainfall data from 1989 to 2018 is considered for the analysis of trend, variability and mean rainfall patterns. From the daily rainfall data monthly rainfall series of each stations are computed. 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 2. Understand district wise observed rainfall trend and variability in annual and South West (SW) monsoon season (June, July, august and September). Daily station rainfall data is utilized for identification of the mean spatial patterns and rainfall intensity trends. From mean and standard deviation (SD), the coefficient of variation (CV) is calculated as follows: Standard Deviation Coeffcient of variation (CV) = × 100 Mean 4 3. State rainfall mean and variability and trend Table 1 demonstrates the mean rainfall (mm) and coefficient (%) of variation for the state of Karnataka for monsoon months, southwest monsoon season and annual for the period 1989- 2018. Contribution of July month to SW monsoon seasonal total rainfall is highest (32%) followed by August (26%), June (24%) and September (18%). On an average 74 % of the annual rainfall is received in SW monsoon season. The variability for monsoon and annual rainfall is 14.5 % and 12.7 % respectively. June July August September JJAS Annual Mean 205.5 269.6 221.2 150.5 846.8 1146.9 CV 22.0 27.7 23.1 35.3 14.5 12.7 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 depicts the time series and trend in rainfall (mm) for June, July, August, September, southwest monsoon season and annual. There is no statistically significant rainfall trend in SW monsoon months, SW monsoon season and annual for Karnataka state. June, July and August indicate the slight downward trend; however, it is statistically insignificant. Rainfall for the month of September show slight increasing statistically insignificant trend. SW monsoon season and annual trend in rainfall demonstrate the downward trend (statistically insignificant trend). Highest rainfall occurred in last 30 years for each monsoon month, SW monsoon season and annual is shown in Table 2. Month/Season/Annual Highest Rainfall received (mm) Year June 311.2 1991 July 395.7 1994 August 340.0 1997 September 261.3 2009 SW Monsoon 1083.6 2007 Annual 1402.3 1997 Table 2. Highest rainfall records for SW monsoon months, SW monsoon season and annual. 5 Fig. 2 Time series and trend of rainfall in mm for the months of June, July, August, September Fig. 3 Time series and trend of rainfall in mm for the southwest monsoon season and annual 6 4. District rainfall mean, variability and trend 4.1 Mean and coefficient of variation Rainfall statistics for the districts of Karnataka for SW monsoon months, SW monsoon season and annual is presented in Table 3. The spatial pattern of rainfall statistics is depicted in Figure 4 and 5. As Karnataka receives maximum amount of rainfall during SW monsoon season, coastal and adjacent districts (Uttar Kannada, Shivamogga, Udupi, Dakshin Kannada and Kodagu) of the Karnataka state receive highest amount of rainfall ranging from 269-1124 mm in June, 583- 1378 mm in July, 442-1000 mm in August, 155-412 mm in September respectively. The average rainfall received for these districts during SW monsoon season and annual is in the range of 1739- 3914 mm and 2108-4474 mm respectively. Inland districts receive less amount of rainfall compared to coastal districts. The mean rainfall received for inland districts of Karnataka during SW monsoon is in the range of 55-269 mm in June, 54-319 mm in July, 71-257 mm in August 90-155 in September 289-1014 in SW monsoon and 530-1319 for the annual respectively. Maximum variation in rainfall is seen in Belagavi, Vijayapur, Yadgir, Raichur, Koppal, Chikkaballapur, Kolar and Bengaluru Urban districts for June, for July it is maximum in Belagavi, Tumakuru, Chikkaballapur, Kolar, Mandya and Chamarajanagar, for September it is maximum in Bagalkot, Koppal, Ballari, Chitradurga, Chamarajanagar and Gadag districts . Belagavi district shows maximum variation in August, monsoon season and in annual scale. JUNE JULY AUGUST SEPTEMBER MONSOON ANNUAL DISTRICT MEAN CV MEAN CV MEAN CV MEAN CV MEAN CV MEAN CV BAGALKOTE 83.5 57 55.9 45 71.6 56 118.7 62 329.6 36 542.8 25 BENGALURU RURAL 71.7 63 89.9 57 116.4 51 151.7 54 429.6 28 796.5 27 BENGALURU URBAN 72.7 60 81.8 54 124.0 58 162.7 51 441.3 29 825.9 26 BELAGAVI 211.9 66 305.1 67 228.2 101 127.6 47 872.8 62 1091.8 51 BALLARI 67.4 54 55.7 59 84.9 57 108.9 63 317.0 31 532.5 24 BIDAR 119.7 50 163.7 61 178.5 45 153.7 58 615.5 28 803.4 24 VIJAYAPUR 79.7 62 64.3 59 78.9 56 124.3 55 347.3 31 530.3 24 CHAMARAJNAGAR 58.6 60 60.8 63 76.7 60 117.9 60 314.1 36 758.8 24 CHIKMAGALUR 312.4 33 486.9 35 370.4 27 167.2 46 1336.9 20 1736.4 18 CHITRADURGA 55.1 53 62.0