CLIMATE RESEARCH AND SERVICES INDIA METEOROLOGICAL DEPARTMENT MINISTRY OF EARTH SCIENCES PUNE Observed Rainfall Variability and Changes over Himachal Pradesh State Met Monograph No.: ESSO/IMD/HS/Rainfall Variability/10(2020)/34 Pulak Guhathakurta, Nitin Narkhede, Preetha Menon, Ashwini Kumar Prasad and Neha Sangwan GOVERNMENT OF INDIA MINISTRY OF EARTH SCIENCES INDIA METEOROLOGICAL DEPARTMENT Met Monograph No.: ESSO/IMD/HS/Rainfall Variability/10(2020)/34 Observed Rainfall Variability and Changes Over Himachal Pradesh State Pulak Guhathakurta, Nitin Narkhede, Preetha Menon, Ashwini Kumar Prasad and Neha Sangwan INDIA METEOROLOGICAL DEPARTMENT PUNE - 411005 1 DOCUMENT AND DATA CONTROL SHEET 1 Document Title Observed Rainfall Variability and Changes Over Himachal Pradesh State 2 Issue No. ESSO/IMD/HS/Rainfall Variability/10(2020)/34 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 3 10 Distribution Unrestricted 11 Language English 12 Authors Pulak Guhathakurta, Nitin Narkhede, Preetha Menon, Ashwini Kumar Prasad and Neha Sangwan 13 Originating Climate Research Division/ Climate Application & Division/ Group User Interface Group/ Hydrometeorology 14 Reviewing and Director General of Meteorology, India Approving Meteorological 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 2 1. Introduction Himachal Pradesh is a state of the Indian Union at the extreme north of the Indian sub-continent roughly between latitudes 30o22′N and 33o12′N and longitudes 75º45′E and 79º04′E, occupying a region of scenic splendor in the western Himalayas. Himachal means Snowy Mountain (hima, “Snow”, achal, “Mountain”). The state (Pradesh) taking its name from Himalayas. The state has an area of 55,673 sq.km and consists of 12 districts. The state is bounded by Jammu and Kashmir on north, Nepal and Tibet on east, Uttaranchal on southeast, Haryana on south and Punjab on west and southwest. The climate of the state varies from place to place depending on the altitude. It varies from hot and sub-humid tropical (450-900 m) in the southern low tracts, warm and temperate (900-1800 m), cool and temperate (1900-2400 m) and cold alpine and glacial (2400-4800 m) in the northern and eastern high mountain ranges. The state may be broadly divided into 3 geographical regions, viz. outer Himalayas, the lesser Himalayas and the greater Himalayas or the Alpines. The outer Himalayas includes the districts of Bilaspur, Hamirpur, Kangra, Una and the lower parts of Mandi, Sirmaur and Solan. The lesser Himalayas includes the parts of Mandi, Sirmaur and parts of Chamba, Kangra and Shimla. The Alpine zone is at an altitude of 4500 m and beyond, includes Kinnaur and parts of Lahaul and Spiti, Chamba districts. Elevation of areas of the state increases as we move from west to east and from south to north. The hills in the outer Himalayas are about 600 m above sea level. The inner Himalayas are marked by gradual elevation towards the Dhauladhar and Pir Panjal ranges and abruptly rises in the Shimla hills, to the south of which is the high peak of Church-Chandni (3647 m) and the rise is gradual towards the north of river Sutlej. 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 Uttar Pradesh 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 3 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. 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 Himachal Pradesh 3. State rainfall mean and variabilityand 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 season rainfall in August month while the July month get 33% of the south west monsoon rainfall. June and September receive 14% and 17% of south west 4 monsoon rainfall resp. Also more than 61% of annual rainfall receives during the southwest monsoon season only. The variability of monsoon rainfall (19.6%) or variability of annual rainfall is also very less (15.5%).Whereas month of June and September shows greater variability in monthly rainfall i.e. 48% as compare to seasonal rainfall. June July August September JJAS Annual Mean 101.4 236.0 248.7 124.1 710.3 1163.3 CV 48.4 29.7 33.0 48.9 19.6 15.5 Table 1 Mean rainfall (mm) and coefficient of variation of the state for the monsoon months, southwest monsoon season and annual rainfall. Fig. 2 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 significantly increasing/decreasing trend. In the monthly rainfall June rainfall show increasing trend while July, August and September rainfall show decreasing trend but both not significant. Both seasonal and annual rainfall show non significantly decreasing trend. During the last 30 years highest rainfall of June and July received in the year 2013 (203.9mm) and 1993(386.9 mm)respectively while highest rainfall of 476.1 in August received in the year 1997 and of 284.5mm in September received in the year 1995. Highest annual rainfall of 1493.9 mm received in the year 1995 and highest southwest monsoon rainfall of 1028.6 mm received in the year 1995. 5 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 4. District rainfall mean, variability and trend 4.1 Mean and coefficient of variation Table 2 gives the rainfall statistics for the districts of Himachal Pradesh for the four monsoon months, southwest monsoon season and annual. It can be seen that four districts viz. Hamirpur, Mandi, Sirmur and Kangra receive highest rainfall over other districts during all the season. Rainfall receives over these districts are around 120-180 mm in June, 290-510mm in July, 380-600mm in August, 150-210mm in September and during the SW monsoon and annual 1000-1500mm.Kinnur district receives lowest rainfall during the SW monsoon season (190mm) while lowest annual rainfall (616mm). June shows greater variability in case of Kinnaurdistrict i.e. 122%, Lahul and Spiti district shows greater variability in July month i.e. 89% whereas 114% and 99% variability in August and September month respectively.Lahul andSpiti district also shows greater variability in southwest monsoon and annual rainfall. Fig.4 shows the overall picture of mean rainfall over districts of state, north eastern parts of state ie. Lahul andSpiti ,Kinnaur district shows less rainfall in June, July month (36-64mm) whereas in month 6 of August(53-100mm) and again in September (36-93mm) with Kullu district. Western end of state shows better mean rainfall condition ranging between (94-500mm) rainfall during monsoon months. The month of Augusthas better rainfall over all state over other months of monsoon. If we see over monsoon seasonaland annual rainfall, western part of state shows better rainfall activity over eastern part, in other words we can say that as we move from west to east rainfall activity reduces.