CLIMATE RESEARCH AND SERVICES METEOROLOGICAL DEPARTMENT MINISTRY OF EARTH SCIENCES PUNE

Observed Rainfall Variability and Changes over 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

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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

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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 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.

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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

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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.

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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

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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 , 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 . 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 60 76.5 62 95.4 60 289.0 36 560.3 30 DAVANAGERE 82.7 44 103.1 46 103.3 39 96.3 54 385.4 26 650.9 25

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DHARWAD 117.5 51 128.4 44 104.7 40 102.6 54 453.1 27 714.0 22 GADAG 77.9 59 58.1 58 70.8 54 104.5 64 311.4 37 548.9 24 KALABURAGI 98.7 51 124.2 55 137.6 45 153.5 48 514.0 27 686.4 21 HASSAN 199.5 43 286.0 47 214.5 40 143.8 43 843.8 28 1260.7 25 HAVERI 110.3 41 141.6 46 114.0 38 90.4 56 456.3 27 733.8 23 694.0 22 988.1 32 679.9 31 259.0 47 2621.1 16 2918.0 15 DAKSHIN KANNADA 938.6 24 1156.9 27 837.1 21 341.5 48 3274.2 15 3942.5 14 KODAGU 592.4 33 850.2 35 605.1 30 257.8 45 2305.6 22 2853.8 19 KOLAR 70.2 61 79.2 69 92.2 52 142.7 49 384.2 26 743.1 25 KOPPAL 76.5 64 53.7 61 86.6 65 124.1 62 340.9 37 563.3 28 MANDYA 60.0 57 59.2 70 80.0 58 114.4 59 313.7 35 715.8 26 MYSURU 88.5 51 96.9 49 90.8 45 94.2 57 370.3 30 779.4 22 RAICHUR 77.6 70 73.2 59 101.6 59 134.7 59 387.1 32 575.4 26 SHIVAMOGGA 496.1 30 799.7 37 585.2 33 216.3 51 2097.2 23 2417.6 21 TUMAKURU 63.7 51 66.8 66 90.7 58 122.2 55 343.4 28 654.1 21 UDUPI 1124.1 21 1377.9 29 1000.0 24 412.2 52 3914.1 13 4473.8 13 RAMNAGARA 82.4 53 97.7 59 128.4 44 151.2 55 459.7 31 862.5 24 CHIKKABALLAPUR 62.9 63 79.2 69 98.2 57 131.7 48 372.0 31 678.6 27 YADGIR 84.6 62 101.7 55 124.5 54 139.0 52 449.8 31 628.0 25

Table 3 Rainfall statistics for the districts of Karnataka for the four monsoon months, southwest monsoon season and annual

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Fig.4 Mean rainfall pattern over districts of Karnataka for June, July, August, September, SW monsoon and annual

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Fig.5 Coefficient of Variation (%) in rainfall over districts of Karnataka

4.2 Trend in district rainfall

District wise rainfall trend for Karnataka state is depicted in figure 6. Statistically significant decreasing trend in rainfall is seen for Dakshin Kannada and Chamarajanagar districts in the month of July and only Dakshin Kannada district during south west monsoon season and annual scale. Statistically significant increasing trend in rainfall is seen in Davangere district for the month of September. The slight upward trend in rainfall for the interior districts of the Karnataka is observed in June and July, however it is statistically insignificant. Remaining districts show statistically insignificant decreasing trend in rainfall for the month of June and July. For the month of August, southwest monsoon season and annual scale non significant increasing trend is seen in the interior districts whereas decreasing trend is seen in the coastal districts. Increasing

10 trend in rainfall is seen in all the districts in September except in Kolar and Chamarajanagar districts.

Fig.6 Trends in district rainfall for June, July, August, September, JJAS and annual

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5. Analysis of Average frequencies for rainfall events of different intensities

5.1 Average frequency of Rainy days

Average frequency of rainy days for the districts of the Karnataka state has been identified (See fig 7 -12). The East-West pattern in average frequency of rainy days has been observed. The coastal and adjacent western districts indicate the higher number of rainy days while interior eastern districts record comparatively lesser number of rainy days.

Fig. 7 Average frequency of rainy days: June Fig. 8 Average frequency of rainy days: July

Fig. 9 Average frequency of rainy days: August Fig. 10 Average frequency of rainy days: September

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Fig. 11 Average frequency of rainy days: JJAS Fig. 12 Average frequency of rainy days: Annual

The average frequency of rainy days for the month of June for the coastal and adjacent western districts (interior eastern districts of Karnataka) is in the range of 11-21 (4-14) days for June, 13- 26 (4-13) days for July, 13-24 (5-13) days for August, 7-14 (5-7) days for September, 45-82 (20- 45) days SW monsoon season and 61-105 (32-61) days for annual.

5.2 Average frequency of Heavy rainfall days

Average frequency of heavy rainfall days for June, July, August, September, SW monsoon and annual is depicted in figure 13-18. Since coastal districts receive highest amount of rainfall for all timescales (pl see figure 4 also), frequency of the heavy rainfall is also found to be high for these districts (Uttar Kannada, Udupi, Dakshin Kannada, Kodagu and western region of Shivamogga, Chikmagalur and Hassan districts). Frequency of heavy rainfall days for remaining district is less as compare to above mentioned districts. Average frequency of heavy rainfall days for the coastal districts (and remaining district) of the Karnataka state is in the range of 1-5 (0.1- 1) days for June, 1.5-7 (0.1-1.4) days for July, 1.5-4 (0.1-0.87) days for August, 0.5-2 (0.1-0.3) days for September, 3-16 (0.5-4) days for SW monsoon and 4-17 (1-4) for annual respectively.

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Fig. 13 Average frequency of heavy rainfall days: Fig. 14 Average frequency of rainy days: July June

Fig. 15 Average frequency of rainy days: August Fig. 16 Average frequency of rainy days: September

Fig. 17 Average frequency of rainy days: JJAS Fig. 18 Average frequency of rainy days: Annual 14

5.3 Average frequency of Dry days

Spatial pattern of average frequency of dry days is similar to mean pattern of rainfall. Frequency of the dry days is found to be lesser for coastal and adjacent districts of Karnataka (Figure 19-24, Uttar Kannada, Udupi, Dakshin Kannada, Kodagu and western region of Shivamogga, Chikmagalur and Hassan districts) while remaining districts records comparatively higher number of dry days. Average frequency of dry days for the coastal districts (and remaining district) of the Karnataka state is in the range of 7-18 (18-25) days for June, 3-16 (16-25) days for July, 7-18 (18-25) days for August, 13-17 (19-23) days for September, 29-68 (68-93) days for SW monsoon and 222-252 (252-296) days for annual respectively.

Fig. 19 Average frequency of dry days: June Fig. 20 Average frequency of dry days: July

Fig. 21 Average frequency of dry days: August Fig. 22 Average frequency of dry days: September

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Fig. 23 Average frequency of dry days: JJAS Fig. 24 Average frequency of dry days: Annual

6. Trends in the frequencies of different rainfall events

6.1 Trend in frequency of Rainy days

Trend in rainy days for June, July, August, September, SW monsoon and annual is computed (Fig. 25-30). Most of the stations indicate significant decrease (significant at 95%) in frequency of rainy days for the month of June. There is no statistically significant trend in frequency of rainy days for Kalaburgi, Yadgir, Udupi and Dakshin Kannada. Most of the stations from central and north Karnataka show upward trend in frequency of rainy days, however, districts from southern most region of the state, viz. Mysuru and Chamarajanagar depict the downward trend for the month of July. Majority of the stations from coastal and adjacent districts (southern region) of the state show decreasing (increasing) trend. Some stations from northern region also reveal upwards trend in frequency of rainy days. Except Chamarajanagar, , Kolar districts majority of the district demonstrate upward trend in rainy days for the month of September. Bagalkot, Koppal and Ballari districts do not indicate any significant trend in frequency of rainy days for the month of September. Indistinct pattern of trend in frequency of rainy days is not seen for SW monsoon season as well as for annual. Most of the station from North (South) region of the state show upward (downward) trend in frequency of rainy for SW monsoon season.

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Fig. 25 Trend in frequency of rainy days: June Fig. 26 Trend in frequency of rainy days: July

Fig. 27 Trend in frequency of rainy days: August Fig. 28 Trend in frequency of rainy days: September

Fig. 29 Trend in frequency of rainy days: JJAS Fig. 30 Trend in frequency of rainy days: Annual

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6.2 Trend in frequency of Heavy rainfall days

Trend in frequency of heavy rainfall days of SW months, SW monsoon season and annual is depicted in figure 31-36. Most of the stations/districts show decreasing trend in frequency of heavy rainfall days for the month of June and July except Koppal and Raichur in June and Koppal, Mandya and Tumakuru in July. Majority of the districts show upward trend in frequency of heavy rainfall days for the months of August and September except Udupi, Dakshin Kannada and Ramanagara district in August and Bidar, Bagalkot, Mysuru, Chamrajanagar, Mandya and Kolar districts for September (indicate downward trend).Maximum number of districts/stations from Western (Eastern) region of the state indicate decreasing (increasing) trend in frequency of Heavy rainfall days for SW monsoon season, however there is no statistically significant trend for Vijaypur and Bagalkot districts. For annual most of the districts/stations report decreasing trend in heavy rainfall days except, Mandya, Chitradurga and Tumakuru (indicate increasing trend).

Fig.31 Trend in frequency of heavy rainfall days: Fig. 32 Trend in frequency of heavy rainfall days: June July

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Fig. 33 Trend in frequency of heavy rainfall days: Fig. 34 Trend in frequency of heavy rainfall days: August September

Fig. 35 Trend in frequency of heavy rainfall days: JJAS Fig. 36 Trend in frequency of heavy rainfall days: Annual

6.3 Trend in frequency of Dry days

The statistically significant trends in frequency of dry days at 95% of significant level is computed for the rain gauge stations of Karnataka state for June, July, August, September, SW monsoon and annual (Figure 37-42).There is no indistinct pattern in trend of frequency of dry days for the month of June, however, Vijaypur, Koppal, Ballari, Shivamogga, Chamarajanagar, Ramanagara district indicate upward trend and Kalaburagi, Yadgir and Bagalkot show downward trend. For the month of July majority of the districts/stations depict statistically significant decreasing trend in frequency of dry days. Central, Coastal and extreme South Eastern region of the state portray rising trend in frequency of dry days while southern and some stations from

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Northern region indicate decreasing trend in frequency of heavy rainfall days for the month of August. Except Chamarajanagar, Ramanagara, Tumakuru and Kolar all other districts indicate the downward trend in frequency of dry days for the month of September. Majority of the stations/districts depict decreasing trend in dry days for SW monsoon as well as annual.

Fig. 37 Trend in frequency of dry days: June Fig. 38 Trend in frequency of dry days: July

Fig. 39 Trend in frequency of dry days: August Fig. 40 Trend in frequency of dry days: September

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Fig. 41 Trend in frequency of dry days: JJAS Fig. 42 Trend in frequency of dry days: Annual

7. Conclusions

Using 30 years (1989-2018) of rainfall data, here we investigated the rainfall pattern, variability and change for Karnataka state. We considered, June, July, August and September, SW Monsoon season and annual time scales for the analysis. The district spatial patterns are considered to study rainfall total and stations are considered to study rainfall intensities. This study brought out many significant features of the rainfall pattern which can be utilized for the water and agricultural management. Some of the important findings are summarized below:

Karnataka state receives maximum rainfall in the month of July (32 % of SW monsoon rainfall) followed by August (26%), June (24%) and September (18%) and contribution of the SW monsoon rainfall to annual total is 74 %. The variability for monsoon and annual rainfall is 14.5 % and 12.7 % respectively. Dakshin Kannada for SW monsoon season and annual time scale indicates statistically significant downward trend in rainfall. No significant trend in rainfall is observed for rest of the districts for SW monsoon and annual timescales. The East-West dipole pattern in spatial distribution of the average frequency of rainy days has been observed. The coastal and adjacent western districts indicate the higher number of rainy days while interior eastern districts record comparatively lesser number of rainy days. 21

The average frequency of rainy days for the month of June for the coastal and adjacent western districts (interior eastern districts of Karnataka) is in the range of 45-82 (20-45) days for SW monsoon season and 61-105 (32-61) days for annual. Frequency of the heavy rainfall is also found to be high for coastal districts (Uttar Kannada, Udupi, Dakshin Kannada, Kodagu and western region of Shivamogga, Chikmagalur and Hassan districts). Frequency of heavy rainfall days for remaining district is less as compare to above mentioned districts. Average frequency of heavy rainfall days for the coastal districts (and remaining district) of the Karnataka state is in the range 3-16 (0.5-4) days for SW monsoon and 4-17 (1-4) for annual respectively. The East-West dipole pattern in frequency of dry days is seen. Frequency of the dry days is found to be lesser for coastal and adjacent districts of Karnataka (Uttar Kannada, Udupi, Dakshin Kannada, Kodagu and western region of Shivamogga, Chikmagalur and Hassan districts) while remaining districts records comparatively higher number of dry days. Average frequency of dry days for the coastal districts (and remaining district) of the Karnataka state is in the range of 222-252 (252-296) days for annual respectively. Indistinct pattern of trend in frequency of rainy days is not seen for SW monsoon season as well as for annual. Most of the station from North (South) region of the state show upward (downward) trend in frequency of rainy for SW monsoon season. Maximum number of districts/stations from Western (Eastern) region of the state indicate decreasing (increasing) trend in frequency of Heavy rainfall days for SW monsoon season, however there is no statistically significant trend for Vijaypur and Bagalkot districts. For annual most of the districts/stations report decreasing trend in heavy rainfall days except, Mandya, Chitradurga and Tumakuru (indicate increasing trend). Majority of the stations/districts depict decreasing trend in dry days for SW monsoon as well as annual.

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Acknowledgement:

The authors acknowledge Secretary, MOES, DGM, India Meteorological Department and Head, Climate Research and Services for guidance, suggestions and encouragement to carry out the works. Acknowledge also to Hydrology section and National Data Centre, India Meteorological Department Pune for making availability of the data.

References:

1. Guhathakurta P, Rajeevan M, Sikka D R and Tyagi A, 2015 “Observed changes in southwest monsoon rainfall over India during 1901–2011”, Int. J. Climatol, 35, 1881-1898. 2. Guhathakurta P, Sreejith O P and Menon P A, 2011 “Impact of climate changes on extreme rainfall events and flood risk in India”, J. Earth System Science. 120, No. 3, 359-373. 3. Guhathakurta P and Rajeevan M, 2008 “Trends in rainfall pattern over India” International J. of Climatology, 28: 1453–1469

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The report brings out observed rainfall variability and trends over the state as an impact of climate change based on recent 30 years of data ( 1981 - 2018 )

Rainfall pattern of monsoon months, south west monsoon season and annual of the state and it’s districts as well as extreme rainfall event of different intensity of stations are analysed.

Observed Rainfall Variability and Changes over Andhra Pradesh State

PREPARED AND DESIGNED AT HYDROMETEOROLOGY SECTION CLIMATE APPLICATION AND USER INTERFACE GROUP CLIMATE RESEARCH AND SERVICES, PUNE