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/18(2020)/42

Pulak Guhathakurta, Arti Bandgar, 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/18(2020)/42

Observed Rainfall Variability and Changes Over Mizoram State

Pulak Guhathakurta, Arti Bandgar, Preetha Menon, Ashwini Kumar Prasad, Neha Sangwan and S C Advani

INDIA METEOROLOGICAL DEPARTMENT PUNE - 411005

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DOCUMENT AND DATA CONTROL SHEET 1 Document Title Observed Rainfall Variability and Changes Over Mizoram State 2 Issue No. ESSO/IMD/HS/Rainfall Variability/18(2020)/42 3 Issue Date January 2020 4 Security Unclassified Classification 5 Control Status Uncontrolled 6 Document Type Scientific Publication 7 No. of Pages 24 8 No. of Figures 42 9 No. of References 3 10 Distribution Unrestricted 11 Language English 12 Authors Pulak Guhathakurta, Arti Bandgar, Preetha Menon, Ashwini Kumar Prasad, Neha Sangwan and S C Advani 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 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 Mizoram state is situated between 21°58’N to 24°35’N latitude and 92°15' E to 93°29' E longitude. It has a geographical area of over 21,087 Sq. km. The tropic of Cancer passes near the capital of the state, Aizwal town. Mizoram occupies the southeast corner of northeastern region of India. Its geographical borders with and in north and in west extended over 123 km, 95 km and 277 km respectively. It shares about 404 km long international boundary on the east and south with and 318 km on the west with . Mizoram is a land of mostly rolling hills, rivers and valleys. There are 21 major hills ranges of different heights which run through the length and breadth of the state with the highest peak ' hill (Blue Mountain) towering 2,065 metres above mean sea level. The mountain ranges are mostly aligned in south direction in parallel series. The ranges are separated from one another by narrow deep river and valleys. The hills are extremely rugged and steep in the state. There are some small patches of flat lands. Eastern part of the state has mainly mountainous topography and overall elevation is higher and steeper slopes than in the western part of the state. The elevation in the eastern part varies from 400 to 2065 m and average elevation in the eastern region is about 1000 m. The western part of the state is characterized by ridge and valley type topography where average elevation is about 450 m.

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 (Guhathakurta et al, 2015; Guhathakurta et al, 2011; Guhathakurta & Rajeevan, 2008 etc). Also, there are limited studies on district rainfall trends and variability of Mizoram state. 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

3 weighted rainfall values of all the districts within the state. Fig.1 gives the location of the districts of 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 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 Location of the districts of Mizoram 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 (27%) of south west monsoon rainfall in August month

4 while the June month get 26% of the south west monsoon rainfall. July and September receive 25% and 22% of south west monsoon rainfall. Also around 67% of annual rainfall receives during the southwest monsoon season only. The variability of monsoon or annual rainfall is also very less.

June July August September JJAS Annual

Mean 430.6 420.0 447.1 368.8 1666.6 2483.2

C V 29.2 30.4 30.9 24.9 19.0 15.6

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 all the monsoon months rainfall show increasing trend. However seasonal rainfall shows increasing trend and annual rainfall does not show any trends. During the last 30 years highest rainfall of June and July received in the year 2003 (755.1mm and 814.4mm) respectively while highest rainfall of 1034.1mm in August received in the year 2017 and of 609.7mm in September received in the year 2007. Highest annual rainfall of 3866.0mm received in the year 2017 and highest southwest monsoon rainfall of 2967.5mm received in the year 2017.

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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

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4. District rainfall mean, variability and trend 4.1 Mean and coefficient of variation Table 1 gives the rainfall statistics for the districts of Mizoram 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 district receives highest rainfall over other districts during all the months and season. Rainfall receives over the district are around 410-435mm in June, 414-442mm in July, 472-502mm in August, 365-386mm in September and during the SW monsoon 1719-1818mm and annual 2629-2693mm. Lowest rainfall receives during the SW monsoon season over district (1314.7mm). Also, receives lowest annual rainfall (2037.6).

JUNE JULY AUGUST SEPTEMBER MONSOON ANNUAL DISTRICT MEAN CV MEAN CV MEAN CV MEAN CV MEAN CV MEAN CV AIZWAL 430.9 29.6 412.4 31.6 447.3 18.5 369.7 26.6 1660.3 13.1 2593.4 12.1 CHAMPHAI 335.0 46.4 332.2 45.2 347.8 39.9 299.7 44.2 1314.7 38.0 2037.6 47.8 KOLASIB 433.6 40.1 435.5 43.2 494.7 40.9 368.9 47.6 1732.6 34.6 2674.5 48.4 455.2 53.5 469.1 58.0 385.0 50.0 354.0 50.2 1663.3 47.0 2428.7 51.7 459.9 47.9 468.8 44.7 502.5 50.4 407.8 35.3 1839.0 37.1 2572.7 48.5 412.3 53.6 340.9 52.5 434.0 49.4 351.1 57.8 1538.3 46.9 2549.6 52.0 SAIHA 447.6 43.3 418.4 50.9 443.4 45.5 401.9 51.7 1711.3 39.7 2564.5 50.0 453.5 49.2 422.2 42.5 393.0 30.9 336.8 35.5 1605.5 28.8 2391.2 46.8 Table1. Rainfall statistics for the districts of Mizoram for the four monsoon months, southwest monsoon season and annual

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Fig.4 Mean rainfall pattern over districts of Mizoram

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

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 no district has shown either increasing or decreasing trend for the month of June, July and September. has shown significant increasing trend in August rainfall. During the whole southwest monsoon season also no district has shown any significant trend. For the annual rainfall two districts viz. Mamit and Champhai show significant decreasing trend while no district showed significant increasing trend.

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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

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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 Mizoram for June, July, August, September, June to September and Annual. Figure 7 shows that in the month of June the maximum number of rainy days lies in the range of 18.6 to 20 days especially in some parts of Lunglei, Saiha, Aizwal, Champhai, Serchhip and Kolasib districts. While minimum number of rainy days lies in the range of 13 to 14.7 days especially in some parts of Mamit, Saiha and Lawngtlai districts. Whereas in remaining districts, the number of rainy days lies in the range of 14.7 to 18.6 days. As shown in the figure 8 in the month of July the maximum number of rainy days lies in the range of 21.57 to 23 days especially in some parts of Kolasib, Aizwal, Lunglei, Saihaand Lawngtlai districts. While minimum number of rainy days lies in the range of 16 to 18.12 days especially in some parts of Mamit, Aizwal, Champhai, Lawngtlai and Saiha districts. Whereas in remaining districts, the number of rainy days lies in the range of 18.12 to 21.57 days. From figure 9 it is seen that in the month of August the maximum number of rainy days lies in the range of 21.3 to 23 days especially in some parts of Kolasib, Aizwal, Lunglei, Lawngtlai and Saiha districts. While minimum number of rainy days lies in the range of 16 to 17.69 days especially in some parts of Aizwal, Champhai, Mamit, Lawngtlai and Saiha districts. Whereas in remaining districts, the number of rainy days lies in the range of 17.69 to 21.3 days. It can be seen from figure 10 that in the month of September the maximum number of rainy days lies in the range of 17.85 to 19 days especially in some parts of Kolasib, Aizwal, Lunglei and Saiha districts. While minimum number of rainy days lies in the range of 13 to 14.38 days especially in some parts of Lawngtlai, Saiha, Mamit, Aizwal and Champhai districts. Whereas in remaining districts, the number of rainy days lies in the range of 14.38 to 17.85 days. During June to September (figure 11) the maximum number of rainy days lies in the range of 76.06 to 80.95 days especially in some parts of Kolasib, Aizwal, Champhai, and Saiha districts. While minimum number of rainy days lies in the range of 56 to 61.35 days especially in some parts of Champhai, Mamit, Lunglei, Serchhip, Saihaand Lawngtlai districts. Whereas in remaining districts, the number of rainy days lies in the range of 61.35 to 76.06 days. During the entire year, shown in figure 12, the maximum number of rainy days lies in the range of 113 to 121 days especially in some parts of Saiha, Lunglei, Serchhip, Aizwal, Champhai

11 and Kolasib districts. While minimum number of rainy days lies in the range of 80 to 88.9 days especially in some parts of Mamit, Lunglei, Champhai, Lawngtlaiand Saiha districts. Whereas in remaining districts, the number of rainy days lies in the range of 88.9 to 113 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

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

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5.2 Average frequency of Heavy rainfall days The average frequency of Heavy rainfall days is calculated for Mizoram 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 lies in the range of 1.36 to 2 days especially in some parts of Aizwal, Serchhip and Lunglei districts. While minimum number of Heavy rainfall days lies in the range of 0.6 to 0.83 days especially in some parts of Lunglei, Saiha, Champhai, Kolasib and Aizwal districts. Whereas in remaining districts, the number of Heavy rainfall days lies in the range of 0.83 to 1.36 days. As shown in figure 14, in the month of July the maximum number of heavy rainfall days lies in the range of 1.16 to 2 days especially in some parts of Kolasib, Aizwal, Lungleiand Serchhip districts. While minimum number of Heavy rainfall days lies in the range of 0.5 to 0.73 days especially in some parts of Champhai, Aizwal, Mamit, Lungleiand Saiha districts. Whereas in remaining districts, the number of Heavy rainfall days lies in the range of 0.73 to 1.16 days. From figure 15, it can be seen that in the month of August the maximum number of heavy rainfall days lies in the range of 1.02 to 2 days especially in some parts of Kolasib, Aizwal and Lunglei districts. While minimum number of Heavy rainfall days lies in the range of 0.4 to 0.61 days especially in some parts of Champhai, Aizwal, Serchhip, Lunglei and Saiha districts. Whereas in remaining districts, the number of Heavy rainfall days lies in the range of 0.61 to 1.02 days. As per figure 16 during September the maximum number of heavy rainfall days lies in the range of 1.08 to 2 days especially in some parts of Kolasib, Aizwal and Lunglei districts. While minimum number of Heavy rainfall days lies in the range of 0.6 to 0.72 days especially in some parts of Kolasib, Champhai, Lunglei, Lawngtlai and Saiha districts. Whereas in remaining districts, the number of Heavy rainfall days lies in the range of 0.72 to 1.08 days. During June to September (figure 17) the maximum number of heavy rainfall days lies in the range of 4.03 to 5 days especially in some parts of Kolasib, Aizwal, Lunglei and Serchhip districts. While minimum number of Heavy rainfall days lies in the range of 2 to 2.74 days especially in some parts of Champhai, Aizwal, Mamit, Lunglei and Saiha districts. Whereas in remaining districts, the number of Heavy rainfall days lies in the range of 2.74 to 4.03 days. During the entire year, shown in figure 18, the maximum number of heavy rainfall days lies in the range of 6.09 to 7 days especially in some parts of Kolasib, Aizwal and Serchhip districts. While minimum number of Heavy rainfall days lies in the range of 3 to 4.03 days especially in

13 some parts of Champhai, Aizwal and Lunglei districts. Whereas in remaining districts, the number of Heavy rainfall days lies in the range of 4.03 to 6.09 days.

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

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

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

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5.3 Average frequency of Dry days The average frequency of dry days is calculated for Mizoram 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 12.8 to 15 days especially in some parts of Lawngtlai, Saiha and Aizwal districts. While minimum number of dry days lies in the range of 7 to 8.73 days especially in some parts of Kolasib. Lunglei, Lawngtlai and Saiha districts. Whereas in remaining districts, the number of dry days lies in the range of 8.73 to 12.8 days.

From figure 20 in the month of July the maximum number of dry days lies in the range of 9.95 to 12 days especially in some parts of Aizwal, Mamit, Champhai, Lunglei, Lawngtlai and Saiha districts. While minimum number of dry days lies in the range of 5 to 6.25 days especially in some parts of Aizwal, Champhai, Serchhip, Lunglei, Lawngtlai and Saiha districts. Whereas in remaining districts, the number of dry days lies in the range of 6.25 to 9.95 days.

As shown in figure 21 in the month of August the maximum number of dry days lies in the range of 10.4 to 12 days especially in some parts of Aizwal, Champhai, Mamit, Lunglei, Lawngtlai and Saiha districts. While minimum number of dry days lies in the range of 5 to 6.8 days especially in some parts of Aizwal, Serchhip, Champhai, Lunglei, Lawngtlai and Saiha districts. Whereas in remaining districts, the number of dry days lies in the range of 6.8 to 10.4 days.

In the month of September (figure 22) the maximum number of dry days lies in the range of 13.1 to 15 days especially in some parts of Aizwal, Champhai, Mamit, Lunglei, Lawngtlai and Saiha districts. While minimum number of dry days lies in the range of 8 to 9.44 days especially in some parts of Aizwal, Serchhip, Lunglei, Lawngtlaiand Saiha districts. Whereas in remaining districts, the number of dry days lies in the range of 9.44 to 13.1 days.

It can be seen that (figure 23) during June to September the maximum number of dry days lies in the range of 43.6 to 49 days especially in some parts of Mamit, Aizwal, Champhai, Lunglei, Lawngtlai and Saiha districts. While minimum number of dry days lies in the range of 23 to 28.8 days especially in some parts of Aizwal, Serchhip, Champhai, Lunglei, Lawngtlai and Saiha

15 districts. Whereas in remaining districts, the number of dry days lies in the range of 28.8 to 43.6 days. During the entire year, from figure 24, the maximum number of dry days lies in the range of 226.3 to 237 days especially in some parts of Mamit, Aizwal, Kolasib, Champhai, Lunglei, Lawngtlai and Saiha districts. While minimum number of dry days lies in the range of 186 to 196.5 days especially in some parts of Aizwal, Serchhip, Champhaiand Lunglei districts. Whereas in remaining districts, the number of dry days lies in the range of 196.5 to 226.3 days.

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 The trend in frequency of rainy days is calculated for the raingauge stations of Mizoram for June, July, August, September, June to September and Annual. From figure 25 in the month of June there is a significant decrease in Rainy days in stations in Kolasib and Serchhip districts. While remaining districts did not show any significant change. Figure 26 shows that in the month of July there is a significant decrease in Rainy days in stations in Aizwal and Lawngtlai districts. While remaining districts did not show any significant change. As per figure 27 in the month of August there is a significant decrease in Rainy days in stations in Kolasib and Aizwal districts. While remaining districts did not show any significant change. It can be seen that (figure 28) in the month of September there is a significant increase in Rainy days in stations in Aizwal district. Whereas there is a significant decrease in Rainy days in stations in . While remaining districts did not show any significant change. In the months of June to September (figure 29) there is a significant increase in Rainy days in stations in Aizwal district. Whereas there is a significant decrease in Rainy days in stations in Kolasib, Aizwal, Serchhip, Lunglei, Lawngtlai districts. While remaining districts did not show any significant change.

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During the entire year, as shown in figure 30, there is a significant decrease in Rainy days in Kolasib, Aizwal, Serchhip, Champhai, Lunglei, Lawngtlai, Saihadistricts. While remaining districts did not show any significant change.

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

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

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

6.2 Trend in frequency of Heavy rainfall days

The trend in frequency of Heavy days is calculated for Mizoram for June, July, August, September, June to September and Annual. From figure 31 in the month of June there is a significant increase in Heavy rainfall days in Aizwal and Lunglei districts. While remaining districts did not show any significant change. Figure 32 shows that in the month of July there is a significant increase in Heavy rainfall days in Kolasib and Aizwal districts. Whereas there is a significant decrease in Heavy rainfall days in Champhai district. While remaining districts did not show any significant change. It can be seen from figure 33 that in the month of August there is a significant increase in Heavy rainfall days in Kolasib, Aizwal, Lunglei and Saiha districts. While remaining districts did not show any significant change. As shown in the figure 34 in the month of September there is a significant increase in Heavy rainfall days in Kolasib, Aizwal and Saiha districts. While remaining districts did not show any significant change. During June to September (figure 35) there is a significant increase in Heavy rainfall days Kolasib, Aizwal, Champhai and Saiha districts. Whereas there is a significant decrease in Heavy rainfall days in Champhai district. While remaining districts did not show any significant change.

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During the entire year, as shown in figure 36, there is a significant increase in Heavy rainfall days in Kolasib, Aizwal, Champhai and Saiha districts. Whereas there is a significant decrease in Heavy rainfall days in Serchhip and Champhai districts. While remaining districts did not show any significant change.

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

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

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Fig. 35 Trend in frequency of heavy rainfall days: Fig. 36 Trend in frequency of heavy rainfall days: JJAS Annual 6.3 Trend in frequency of Dry days The Trend in frequency of dry days is calculated for Mizoram for June, July, August, September, June to September and Annual. From figure 37 in the month of June there is a significant increase in dry days in Kolasib and Serchhip 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 Aizwal and Lungleidistricts. While remaining districts did not show any significant change. It can be seen from figure 39 that in the month of August there is a significant increase in dry days in Kolasib, Aizwal and Lunglei districts. Whereas there is a significant decrease in dry days in Serchhip and Saiha districts. While remaining districts did not show any significant change. As per figure 40 in the month of September there is a significant increase in dry days in Kolasib district. While remaining districts did not show any significant change. In the months of June to September, as shown in figure 41 there is a significant increase in dry days in Kolasib and Aizwal districts. While remaining districts did not show any significant change. During the entire year (figure 42) there is a significant increase in dry days in Kolasib and Aizwal districts. Whereas there is a significant decrease in dry days in . 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: Mizoram gets maximum rainfall in August (27% of SW monsoon rainfall) followed by June (26 % of SW monsoon rainfall). 67% of annual rainfall receives during southwest monsoon rainfall (June –September). Lunglei district of Mizoram receives 71-72% of annual rainfall in SW monsoon season while Champhai district receive 64-65% of annual rainfall in SW monsoon season. No significant increasing/decreasing trends in June, July, August, September monthly rainfall. Kolasib district receives highest rainfall over other districts during all the months and season. Rainfall receives over the district are around 410-435mm in June, 414-442mm in July, 472-502mm in August, 365-386mm in September and during the SW monsoon 1719-1818mm and annual 2629- 2693mm. Lowest rainfall receives during the SW monsoon season over Champhai district (1314.7mm). Also Champhai district receives lowest annual rainfall (2037.6). Lunglei district has shown significant increasing trend in August rainfall. During the whole southwest monsoon season no district has shown any significant trend. For the annual rainfall two districts viz. Mamit and Champhai show significant decreasing trend while no district showed significant increasing trend.In annual rainfall Palghar shows significant increasing trend while Aurangabad and Parbhanishow significant decreasing trend. Maximum number of rainy days (daily rainfall >=2.5mm) lies in the range of 76.06 to 80.95 days especially in some parts of Kolasib, Aizwal, Champhai, and Saiha districts. While minimum number of rainy days lies in the range of 56 to 61.35 days especially in some parts of Champhai, Mamit, Lunglei, Serchhip, Saihaand Lawngtlai districts. Whereas in remaining districts, the number of rainy days lies in the range of 61.35 to 76.06 days. For heavy to extremely heavy rainfall ( daily rainfall >=6.5mm) days lies in the range of 4.03 to 5 days especially in some parts of Kolasib, Aizwal, Lunglei and Serchhip districts. While minimum number of Heavy rainfall days lies in the range of 2 to 2.74 days especially in some parts of Champhai, Aizwal, Mamit, Lunglei and Saiha districts. Whereas in remaining districts, the number of Heavy rainfall days lies in the range of 2.74 to 4.03 days. During June to September the maximum number of dry days lies in the range of 43.6 to 49 days especially in some parts of Mamit, Aizwal, Champhai, Lunglei, Lawngtlai and Saiha districts.

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While minimum number of dry days lies in the range of 23 to 28.8 days especially in some parts of Aizwal, Serchhip, Champhai, Lunglei, Lawngtlai and Saiha districts. Whereas in remaining districts, the number of dry days lies in the range of 28.8 to 43.6 days. During the period June to September there is a significant increase in Rainy days in stations in Aizwal district. Whereas there is a significant decrease in Rainy days in stations in Kolasib, Aizwal, Serchhip, Lunglei, Lawngtlai districts. While remaining districts did not show any significant change. During the entire year there is a significant decrease in Rainy days in Kolasib, Aizwal, Serchhip, Champhai, Lunglei, Lawngtlai, Saiha districts. While remaining districts did not show any significant change. During the period June to September there is a significant increase in Heavy rainfall days Kolasib, Aizwal, Champhai and Saiha districts. Whereas there is a significant decrease in Heavy rainfall days in Champhai district. While remaining districts did not show any significant change. During the entire year there is a significant increase in Heavy rainfall days in Kolasib, Aizwal, Champhai and Saiha districts. Whereas there is a significant decrease in Heavy rainfall days in Serchhip and Champhai districts. While remaining districts did not show any significant change. During June to September there is a significant increase in dry days in Kolasib and Aizwal districts. While remaining districts did not show any significant change. During the entire there is a significant increase in dry days in Kolasib and Aizwal districts. Whereas there is a significant decrease in dry days in Lawngtlai district. While remaining districts did not show any significant change. 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 of 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 State

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