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/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

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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 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

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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 () 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 . 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

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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.

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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

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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, and 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 district (815.9 mm) while Udham Singh Nagar district receives lowest annual rainfall (962.00 mm).

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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 19.1 137.3 95.1 340.5 51.0 361.2 44.3 193.2 68.1 1032.2 31.1 1184.8 48.2 181.1 72.6 403.1 49.0 357.0 47.2 254.1 77.3 1193.1 48.4 1429.7 45.4 167.7 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. Rainfall statistics for the districts of Uttarakhand for the four monsoon months, southwest monsoon season and annual

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Fig.4 Mean rainfall pattern over districts of Uttarakhand

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Fig.5 Coefficient of Variation (%) over districts of Uttarakhand

4.2 Trend in district rainfall Fig.6 shows the trends in district rainfall for (a) June, (b) July (c) August (d) September (e) JJAS and (f) annual. It can be seen that June rainfall has shown significant increasing trend in the district Chamoli and while no district has shown any significant dencreasing trend. For the July month significant trend has been noticed in 5 districts viz. Nainital, Almora, Bageshwar, Chamoli and Rudraprayag districts (significant increasing trend). Only of has shown significant increasing trend in August rainfall while September rainfall has shown no significant increasing or decreasing trends in any of districts. For the whole southwest monsoon season as well as annual rainfall, four districts viz. Nainital, Bageshwar, Chamoli and Rudraprayag have shown significant increasing trend while only one district has shown significant decreasing trend i.e. Pauri Garhwal.

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a b

c d

e f Fig.6 Trends in district rainfall for (a) June, (b) July (c) August (d) September (e) JJAS and (f) annual

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

5.1 Average frequency of Rainy days The average frequency of rainy days is calculated for Uttarakhand for June, July, August, September, June to September and Annual. Figure 7 shows that in the month of June the maximum

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number of rainy days lies in the range of 8 to 10 days especially in some parts of , Almora, Nainital, Chamoli, Uttarakashi and districts. While minimum number of rainy days lies in the range of 4 to 5 days especially in Haridwar, Pauri, Garhwal, Udham Singh Nagar, most parts of Nainital and some parts of Almora, Uttarakashi, TehriGarhwal and Dehradun districts. Whereas in remaining districts, the number of rainy days lies in the range of 6 to 8 days.

Figure 8 shows that in the month of July the maximum number of rainy days lies in the range of 16 to 18 days especially in some parts of Pithoragarh, Chamoli, andDehradundistricts. While minimum number of rainy days lies in the range of 9 to 11 days especially in Udham Singh Nagar and some parts of Haridwar, Tehri Garhwal, Pauri Garhwal, Almora and Nainital districts. Whereas in remaining districts, the number of rainy days lies in the range of 11 to 15 days.

Figure 9 shows that in the month of August the maximum number of rainy days lies in the range of 15 to 17 days especially in some parts of Pithoragarh, Chamoli, Uttarkashi,Pauri Garhwaland Dehradun districts. While minimum number of rainy days lies in the range of 9 to 11 days especially inUdham Singh Nagar, Champawat and some parts of Nainital, Almora, Bageshwar, PauriGarhwal, TehriGarhwal and Haridwar districts. Whereas in remaining districts, the number of rainy days lies in the range of 11 to 15 days.

Figure 10 shows that in the month of September the maximum number of rainy days lies in the range of 9 to 10 days especially in some parts Pithoragarh, Chamoli, Uttarkashi, Almora, Nainitaland Dehradun districts. While minimum number of rainy days lies in the range of 5 to 6 days especially in some parts of Udham Singh Nagar, Champawat, Nainital, Almora, Rudraprayag, Pauri Garhwal, Tehri Garhwal and Haridwar districts. Whereas in remaining districts, the number of rainy days lies in the range of 6 to 9 days.

Figure 11 shows that during June to September the maximum number of rainy days lies in the range of 43 to 47 days especially in some parts of Pithoragarh, Chamoli, Uttarkashi, Almora, Nainital, Pauri Garhwal and Dehradun districts. While minimum number of rainy days lies in the range of 29 to 32 days especially in some parts of Udham Singh Nagar, Nainital, Almora, Pauri Garhwal, Tehri Garhwal, Haridwar and Uttarkashi districts. Whereas in remaining districts, the number of rainy days lies in the range of 32 to 43 days.

Figure 12 shows that during the entire year the maximum number of rainy days lies in the range of 60 to 66 days especially in some parts of Pithoragarh, Chamoli, Uttarkashi, Almora, Nainitaland Dehradun districts. While minimum number of rainy days lies in the range of 37 to 43 days especially in some parts of Udham Singh Nagar, Nainital, Almora, Pauri Garhwal, Tehri Garhwal, Haridwar and

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Champawat districts. Whereas in remaining districts, the number of rainy days lies in the range of 43 to 60 days.

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

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

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

5.2 Average frequency of Heavy rainfall days

The average frequency of Heavy rainfall days is calculated for Uttarakhand for June, July, August, September, June to September and Annual. Figure 13 shows that in the month of June the maximum number of heavy rainfall days is only upto 1 day especially in some parts of Pithoragarh, Nainital, Pauri Garhwal, Dehradun, Chamoli and Uttarakashi districts. While minimum number of Heavy rainfall days lies in the range of 0.2 to 0.5 days especially in some parts ofUttarakashi, Dehradun, Chamoli, Almora, Nainital , Pauri Garhwal and Tehri Garhwal districts. Whereas in remaining districts, the number of Heavy rainfall days lies in the range of 0.2 to 0.5 days.

Figure 14 shows that in the month of July the maximum number of heavy rainfall days lies in the range of 1 to 2 days especially in some parts of Pithoragarh, Nainital, Pauri Garhwal and Haridwar districts. While minimum number of Heavy rainfall days lies in the range of 0.4 to 0.7 days especially in some parts of Uttarakashi, Chamoli, Pauri Garhwal, Tehri Garhwal, Almora and Pithoragarh districts. Whereas in remaining districts, the number of Heavy rainfall days lies in the range of 0.7 to 1 days.

Figure 15 shows that in the month of August the maximum number of heavy rainfall days lies in the range of 1 to 2 days especially in some parts of Pithoragarh, Nainital, Pauri Garhwal and Dehradun districts. While minimum number of Heavy rainfall days lies in the range of 0.4 to 0.6 days especially in some parts of Uttarakashi, Dehradun, Chamoli, Tehri Garhwal and Almora districts. Whereas in remaining districts, the number of Heavy rainfall days lies in the range of 0.6 to 1.4 days. Figure 16 shows that during September the maximum number of heavy rainfall days lies in the range of 0.6 to 1 day especially in some parts of Nainital, Almora, Pauri Garhwaland Dehradun districts. While minimum number of Heavy rainfall days lies in the range of 0.1 to 0.3 days especially in some

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parts of Uttarakashi, Chamoli, Tehri Garhwal, Pauri Garhwaland Pithoragarh districts. Whereas in remaining districts, the number of Heavy rainfall days lies in the range of 0.3 to 0.6 days.

Figure 17 shows that during June to September the maximum number of heavy rainfall days lies in the range of 3.5 to 4 days especially in some parts of Pithoragarh, Nainital, Pauri Garhwal and Dehradun districts. While minimum number of Heavy rainfall days lies in the range of 1 to 2 days especially in some parts of Uttarakashi, Chamoli, Tehri Garhwal, Pauri Garhwal, Almora and Pithoragarh districts. Whereas in remaining districts, the number of Heavy rainfall days lies in the range of 2 to 3.5 days.

Figure 18 shows that during the entire year the maximum number of heavy rainfall days lies in the range of 3.8 to 5 days especially in some parts of Pithoragarh, Nainital, Pauri Garhwal and Dehradun districts. While minimum number of Heavy rainfall days lies in the range of 1 to 2 days especially in some parts of Uttarakashi, Chamoli, Tehri Garhwal, Pauri Garhwal, Almora and Pithoragarh districts. Whereas in remaining districts, the number of Heavy rainfall days lies in the range of 2 to 3.8 days.

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

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Fig. 15 Average frequency of heavy rainfall Fig. 16 Average frequency of heavy rainfall days: August days: September

Fig. 17 Average frequency of heavy rainfall Fig. 18 Average frequency of heavy rainfall days: JJAS days: Annual

5.3 Average frequency of Dry days The average frequency of dry days is calculated for Uttarakhand for June, July, August, September, June to September and Annual. Figure 19 shows that in the month of June the maximum number of dry days lies in the range of 22 to 24 days especially in some parts of Udham Singh Nagar, Nainital, Almora, Pauri Garhwal, Haridwar and Uttarkashi districts. While minimum number of dry days lies in the range of 17 to 18days especially in some parts of Pithoragarh, Champawat, Almora, Chamoli, Uttarkashi and Dehradun districts. Whereas in remaining districts, the number of dry days

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lies in the range of 18 to 21 days.

Figure 20 shows that in the month of July the maximum number of dry days lies in the range of 17 to 19 days especially in some parts Udham Singh Nagar, Nainital, Almora, Pauri Garhwal, Tehri Garhwal, Haridwar and Uttarakashi districts. While minimum number of dry days lies in the range of 10 to 12 days especially in some parts of Pithoragarh, Champawat, Almora, Pauri Garhwal, Chamoli, Uttarkashi and Dehradun districts. Whereas in remaining districts, the number of dry days lies in the range of 12 to 17 days.

Figure 21 shows that in the month of August the maximum number of dry days lies in the range of 17 to 19 days especially in some parts of Udham Singh Nagar, Nainital, Almora, Pauri Garhwal, Tehri Garhwal, Dehradun and Uttarkashi districts. While minimum number of dry days lies in the range of 11 to 12 days especially in some parts of Pithoragarh, Almora, Pauri Garhwal, Chamoli, Uttarakashi, Dehradun and Nainital districts. Whereas in remaining districts, the number of dry days lies in the range of 12 to 17 days.

Figure 22 shows that in the month of September the maximum number of dry days lies in the range of 21 to 23 days especially in some parts of Udham Singh Nagar, Nainital, Almora, Pauri Garhwal, Tehri Garhwal and Dehradun districts. While minimum number of dry days lies in the range of 16 to 17 days especially in some parts of Pithoragarh, Almora, Pauri Garhwal, Chamoli, Uttarkashi, Dehradun and Nainital districts. Whereas in remaining districts, the number of dry days lies in the range of 17 to 21 days.

Figure 23 shows that during June to September the maximum number of dry days lies in the range of 73 to 79 days especially in some parts of Udham Singh Nagar, Nainital, Almora, Pauri Garhwal, Tehri Garhwal and Haridwar districts. While minimum number of dry days lies in the range of 50 to 56 days especially in some parts of Pithoragarh, Almora, Chamoli, Uttarkashi, Dehradun and Nainitaldistricts. Whereas in remaining districts, the number of dry days lies in the range of 56 to 73 days.

Figure 24 shows that during the entire year the maximum number of dry days lies in the range of 270 to 284 days especially in some parts of Udham Singh Nagar, Nainital, Almora, Pauri Garhwal and Haridwar districts. While minimum number of dry days lies in the range of 219 to 232 days especially in some parts of Pithoragarh, Champawat, Chamoli, Uttarkashi, Dehradun and Pauri Garhwal districts. Whereas in remaining districts, the number of dry days lies in the range of 232 to 270 days.

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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

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

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6 Trends in the frequencies of different rainfall events

6.1Trend in frequency of Rainy days The Trend in frequency of rainy days is calculated for the raingauge stations of Uttarakhand for June, July, August, September, June to September and Annual. Figure 25 shows that in the month of June there is a significant decrease in Rainy days in stations in Uttarkashi and Dehradun districts. While remaining districts did not show any significant change.

Figure 26 shows that in the month of July there is a significant increase in Rainy days in stations in Chamoli and Pithoragarh districts. Whereas there is a significant decrease in Rainy days in stations in Uttarkashidistrict. While remaining districts did not show any significant change.

Figure 27 shows that in the month of August there is a significant increase in Rainy days in stations in . Whereas there is a significant decrease in Rainy days in stations in Almora, Uttarkashi, Dehradun districts. While remaining districts did not show any significant change.

Figure 28 shows that in the month of September there is a significant decrease in Rainy days in stations in Pauri Garhwal, Uttarkashi and Dehradun districts. While remaining districts did not show any significant change.

Figure 29 shows that in the months of June to September there is a significant increase in Rainy days in stations in Pithoragarh and Chamoli districts. Whereas there is a significant decrease in Rainy daysin stations in Uttarkashi, Pauri Gharwal, Almora and Dehradun districts. While remaining districts did not show any significant change.

Figure 30 shows that during the entire year there is a significant increase in Rainy days in Pithoragarh and Chamoli districts. Whereas there is a significant decrease in Rainy days in Uttarkashi, Pauri Gharwal, Almora and Dehradun districts. While remaining districts did not show any significant change.

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

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

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

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6.2 Trend in frequency of Heavy rainfall days

The Trend in frequency of Heavy days is calculated for Uttarakhand for June, July, August, September, June to September and Annual. Figure 25 shows that in the month of June there is a significant increase in Heavy rainfall days in Chamoli and Pithoragarh districts. While remaining districts did not show any significant change.

Figure 31 shows that in the month of July there is a significant increase in Heavy rainfall days in Chamoli, Champawat, Tehri Garhwal and Pithoragarh districts. Whereas there is a significant decrease in Heavy rainfall days in PauriGarhwal district. While remaining districts did not show any significant change.

Figure 32 shows that in the month of August there is a significant increase in Heavy rainfall days in Pauri Garhwal, Tehri Garhawal and Nainital districts. While remaining districts did not show any significant change.

Figure 33 shows that in the month of September there is a a significant decrease in Heavy rainfall days in Uttarkashi districts. While remaining districts did not show any significant change.

Figure 35 shows that during June to September there is a significant increase in Heavy rainfall days in Pithoragarh, Almora, Chamoli, Pauri Garhwal districts. Whereas there is a significant decrease in Heavy rainfall days in Almora, Pauri Garhwal, Uttarkashi districts. While remaining districts did not show any significant change.

Figure 36 shows that during the entire year there is a significant increase in Heavy rainfall days in Pithoragarh, Nainital, Chamoli, Tehri Garhwal districts. Whereas there is a significant decrease in Heavy rainfall days in Almora, Pauri Garhwal, Uttarakshi and Dehradun districts. While remaining districts did not show any significant change.

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

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

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6.3 Trend in frequency of Dry days

The Trend in frequency of dry days is calculated for Uttarakhand for June, July, August, September, June to September and Annual. Figure 37 shows that in the month of June there is a significant increase in dry days in Pauri Garhwal, Dehradun and Uttarkashi districts. While remaining districts did not show any significant change.

Figure 38 shows that in the month of July there is a significant increase in dry days in Uttarakashi districts. Whereas there is a significant decrease in dry days in Champawat, Pithoragarh, Almora, Chamoli, Uttarkashidistricts. While remaining districts did not show any significant change.

Figure 39 shows that in the month of August there is a significant increase in dry days in Almora, Dehradun and Uttarkashi districts. Whereas there is a significant decrease in dry days in Chamoli district. While remaining districts did not show any significant change.

Figure 40 shows that in the month of September there is a significant increase in dry days in Dehradun and Uttarkashi districts. Whereas there is a significant decrease in dry days in Tehri Garhwal districts. While remaining districts did not show any significant change.

Figure 41 shows that in the month of June to September there is a significant increase in dry days in Pithoragarh and Pauri Garhwal districts. Whereas there is a significant decrease in dry days in . While remaining districts did not show any significant change.

Figure 42 shows that in the month of during the entire year there is a significant increase in dry days in Pithoragarh, Nainital, Dehradun and Pauri Garhwal districts. While remaining districts did not show any significant change.

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

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

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

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7. Conclusions

In the present study we have investigated the rainfall pattern and it its variability and also changes based on recent 30 years data. In the analysis we have considered monsoon months, the monsoon season and annual scale. The spatial scale has been considered from state to district for study of rainfall total and stations are being considered for seeing intensities of rainfall. The analysis brought many significant features of rainfall pattern and can be used for water agricultural managements. Some of the important results can be summarized as:

 Uttarakhand gets maximum rainfall in July (35% of SW monsoon rainfall) followed by August (33 % of SW monsoon rainfall).

 79% of annual rainfall receives during southwest monsoon rainfall (June – September).

 Pauri Garhwal and Champawat districts of Uttarakhand receive 90-93% of annual rainfall in SW monsoon season while Chamoli and Uttarkashi districts receive 70% of annual rainfall in SW monsoon season.

 No significant increasing/decreasing trends in June, July, August, September monthly rainfall.

 Maximum rainfall receive during the SW monsoon season over the districts Pittorgarh, Chapawat and Dehradun (1400mm -1600mm) while Uttarkashi and Almora receive lowest rainfall (800-900mm). Almora district receives lowest rainfall of 816mm.

 Maximum rainfall receives during the year over the Pittorgarh district (2045.10 mm) while Udham Singh Nagar receives lowest annual rainfall of 962mm.

 Significant increasing trend has been noticed in Nainital, Bageshwar, Chamoli and Rudraprayag districts while Pauri shows significant decreasing trend in both the SW monsoon as well as annual rainfall.

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 During June to September the maximum number of rainy days (daily rainfall >=2.5mm) lies in the range of 43 to 47 days especially in some parts of Pithoragarh, Chamoli, Uttarkashi, Almora, Nainital, Pauri Garhwal and Dehradun districts. While minimum number of rainy days lies in the range of 29 to 32 days especially in some parts of Udham Singh Nagar, Nainital, Almora, Pauri Garhwal, Tehri Garhwal, Haridwar and Uttarkashi districts. Whereas in remaining districts, the number of rainy days lies in the range of 32 to 43 days.

 For heavy to extremely heavy rainfall (daily rainfall >=6.5mm) during June to September the maximum number of heavy rainfall days lies in the range of 3.5 to 4 days especially in some parts of Pithoragarh, Nainital, Pauri Garhwal and Dehradun districts. While minimum number of Heavy rainfall days lies in the range of 1 to 2 days especially in some parts of Uttarakashi, Chamoli, Tehri Garhwal, Pauri Garhwal, Almora and Pithoragarh districts. Whereas in remaining districts, the number of Heavy rainfall days lies in the range of 2 to 3.5 days.

 For number of dry days during June to September, the maximum number of dry days lies in the range of 73 to 79 days especially in some parts of Udham Singh Nagar, Nainital, Almora, Pauri Garhwal, Tehri Garhwal and Haridwar districts. While minimum number of dry days lies in the range of 50 to 56 days especially in some parts of Pithoragarh, Almora, Chamoli, Uttarkashi, Dehradun and Nainital districts. Whereas in remaining districts, the number of dry days lies in the range of 56 to 73 days.

 During the period June to September there is there is a significant increase in Rainy days in stations in Pithoragarh and Chamoli districts. Whereas there is a significant decrease in Rainy days in stations in Uttarkashi, Pauri Gharwal, Almora and Dehradun districts. While remaining districts did not show any significant change.

 During the entire year there is a significant increase in Rainy days in Pithoragarh and Chamoli districts. Whereas there is a significant decrease in Rainy days in Uttarkashi, Pauri Gharwal, Almora and Dehradun districts. While remaining districts did not show any significant change.

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 During the period June to September there is a significant increase in Heavy rainfall days in Pithoragarh, Almora, Chamoli, Pauri Garhwal districts. Whereas there is a significant decrease in Heavy rainfall days in Almora, Pauri Garhwal, Uttarkashi districts. While remaining districts did not show any significant change.

 During the entire year there is a significant increase in Heavy rainfall days in Pithoragarh, Nainital, Chamoli, Tehri Garhwal districts. Whereas there is a significant decrease in Heavy rainfall days in Almora, Pauri Garhwal, Uttarakshi and Dehradun districts. While remaining districts did not show any significant change.

 During June to September there is a significant increase in dry days in Pithoragarh and Pauri Garhwal districts. Whereas there is a significant decrease in dry days in Almora district. While remaining districts did not show any significant change.

 During the entire year there is a significant increase in dry days in Pithoragarh, Nainital, Dehradun and Pauri Garhwal districts. While remaining districts did not show any significant change.

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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 for making availability of the data.

References:

1. Malik A, Kumar A, Guhathakurta P and Kisi O, 2019 “Spatial-temporal trend analysis of seasonal and annual rainfall (1966–2015) using innovative trend analysis method with significance test”, Arabian Journal of Geosciences 12:328, https://doi.org/10.1007/s12517-019-4454-5. 2. 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. 3. 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. 4. 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 State

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