CLIMATE RESEARCH AND SERVICES INDIA METEOROLOGICAL DEPARTMENT MINISTRY OF EARTH SCIENCES PUNE Observed Rainfall Variability and Changes over Uttarakhand State Met Monograph No.: ESSO/IMD/HS/Rainfall Variability/28(2020)/52 Pulak Guhathakurta, Arti Bandgar, Preetha Menon, Ashwini Kumar Prasad, S T Sable and Neha Sangwan GOVERNMENT OF INDIA MINISTRY OF EARTH SCIENCES INDIA METEOROLOGICAL DEPARTMENT Met Monograph No.: ESSO/IMD/HS/Rainfall Variability/28(2020)/52 Observed Rainfall Variability and Changes Over Uttarakhand State Pulak Guhathakurta, Arti Bandgar, Preetha Menon, Ashwini Kumar Prasad, S.T. Sable and Neha Sangwan INDIA METEOROLOGICAL DEPARTMENT PUNE - 411005 1 DOCUMENT AND DATA CONTROL SHEET 1 Document Title Observed Rainfall Variability and Changes Over Uttarakhand State 2 Issue No. ESSO/IMD/HS/Rainfall Variability/28(2020)/52 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, Arti Bandgar, Preetha Menon, Ashwini Kumar Prasad, S.T. Sable and Neha Sangwan 13 Originating Climate Research Division/ Climate Application & User Division/ Group Interface Group/ Hydrometeorology 14 Reviewing and Director General of Meteorology, India Meteorological Approving Department, New Delhi Authority 15 End users Central and State Ministries of Water resources, agriculture and civic bodies, Science and Technology, Disaster Management Agencies, Planning Commission of India 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 rent 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 Uttarakhand state is located between 28°43’ - 31°27’ N latitudes and 77°34’ - 81°02’ E longitudes in the northern part of India. The state is mostly hilly and has international boundary with China (Tibet) in the north and Nepal in the east and state boundary with Himachal Pradesh in the northwest. The state has foothills areas in the south and southwest which are bounded by Uttar Pradesh. Uttarakhand state has total geographical area of 53,485 sq. km, of which 86% is mountainous and 65% is covered by forest. The state is rich in natural resources especially water and forests with many glaciers, perennial rivers, dense forests and snow-capped mountain peaks. The most of the northern parts of state are part of greater Himalaya ranges covered by the high mountain peaks and glaciers. Two of India’s mightiest rivers Ganga and Yamuna originate in the glaciers of Uttarakhand. Uttarakhand lies on the south slope of Himalaya ranges and the climate varies from sub-tropical forests at lower elevation to glaciers at higher elevation. The altitude in the state varies from 200 to 7817 metre above mean sea level. Within this altitudinal variation state comprises five litho tectonically and physiographical distinct sub-divisions namely, Outer Himalaya comprising Tarai and Bhabhar, Sub-Himalayan belt of Siwalik, the Lesser Himalaya, the Great Himalaya and the Trans-Himalaya or Tethys. The highest elevations are covered by ice and snow. The upper Gangetic plains, moist deciduous forests and the drier Tarai savanna and grassland cover the low lands along the border of Uttar Pradesh. 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 (Malik et al, 2019; Guhathakurta et al, 2015; Guhathakurta et al, 2011; Guhathakurta & Rajeevan, 2008 etc). Also there are limited studies available on observed rainfall analysis, trend and variability of the state only. 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 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). 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 Fig.1 gives the location of the districts of the state. Fig. 1 Location of the districts of Uttarakhand 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 (35%) of south west monsoon rainfall in July month while the August month get 33% of the south west monsoon rainfall. June and September receive 15% and 17% of south west monsoon rainfall. Also 79% of annual rainfall receives during the southwest monsoon season only. The variability of monsoon or annual rainfall is 21% and 19% respectively. 4 June July August September JJAS Annual Mean 162.1 382.0 360.2 189.7 1093.8 1385.5 C V 57.5 23.6 28.5 56.3 21.2 18.5 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, 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 June and July rainfall show increasing trend while August and September rainfall show no trend. Both seasonal and annual rainfall show increasing trend. During the last 30 years highest rainfall of June and July received in the year 2013 and 2003 (481.7mm and 523.5 mm respectively) while highest rainfall of 539.7mm in August received in the year 2011 and of 472.8mm in September received in the year 1993. Highest annual rainfall of 1928.5mm received in the year 2007 and highest southwest monsoon rainfall of 1494.7mm received in the year 2007. Fig. 2 Time series of rainfall in mm for the months of June, July, August, September and trends 5 Fig. 3 Time series of rainfall in mm for the southwest monsoon season and annual trends 4. District rainfall mean, variability and trend 4.1 Mean and coefficient of variation Table 2 gives the rainfall statistics for the districts of Uttarakhand for the four monsoon months, southwest monsoon season and annual while Fig.4-5 show the spatial pattern of these statistics. It can be seen that districts like Pitorgarh, Champawat and Bageshwar receive highest rainfall in comparison with the other districts during all the months and season.Rainfall receives over these districts are around 200-300 mm in June, 1400-1500 mm in July, 1200-1300 mm in August, 600- 700 mm in September and during the SW monsoon and annual 4000-5500 mm. Lowest rainfall receives during the SW monsoon season over Almora district (815.9 mm) while Udham Singh Nagar district receives lowest annual rainfall (962.00 mm). 6 JUNE JULY AUGUST SEPTEMBER MONSOON ANNUAL DISTRICT MEAN CV MEAN CV MEAN CV MEAN CV MEAN CV MEAN CV ALMORA 147.3 69.7 278.2 42.4 238.3 48.3 141.1 80.7 815.9 50.9 1059.3 54.0 CHAMOLI 112.4 81.1 295.8 45.5 279.4 58.5 132.2 82.7 861.7 51.9 1235.2 52.1 CHAMPAWAT 239.3 55.0 494.4 44.5 443.7 45.4 284.4 66.5 1466.0 34.8 1625.4 49.1 DEHRA DUN 178.9 84.3 503.5 28.9 508.3 26.4 232.2 63.3 1422.9 22.0 1699.2 19.1 HARIDWAR 137.3 95.1 340.5 51.0 361.2 44.3 193.2 68.1 1032.2 31.1 1184.8 48.2 NAINITAL 181.1 72.6 403.1 49.0 357.0 47.2 254.1 77.3 1193.1 48.4 1429.7 45.4 PAURI 167.7 76.7 431.6 68.5 472.1 61.7 201.4 89.1 1191.4 60.5 1285.5 62.1 GARHWAL PITHORGARH 256.5 64.7 565.9 61.7 483.6 53.5 249.8 75.5 1579.3 54.8 2045.1 58.2 TEHRI 129.8 70.4 309.2 45.3 287.1 50.5 167.6 83.1 909.2 36.7 1197.2 35.7 GARHWAL UTTAR KASHI 131.8 80.8 310.5 36.8 284.7 45.4 138.1 47.4 864.2 36.3 1241.8 42.5 UDHAM SINGH 144.7 106.8 322.1 65.3 323.7 64.5 185.1 89.3 1012.9 65.2 962.0 57.4 NAGAR RUDRA 170.6 64.6 358.5 42.2 350.3 49.0 164.1 63.3 1042.6 45.8 1351.8 52.3 PRAYAG BAGESWAR 206.7 79.0 417.7 56.0 341.4 63.5 133.8 85.5 1072.9 55.3 1356.8 52.8 Table 2.