Recent Trend in Temperature and Precipitation Extremes over India

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1 Recent Trend in Temperature and Precipitation Extremes over India Prof. G. P. Singh & Jai Ho Oh Department of Geophysics, Institute of Science, Banaras Hindu University, Varanasi, India & Department of Environmental Atmospheric Sciences, Pukyong National University, Busan, South Korea

2 INTRODUCTION There is general consensus within the scientific community that global surface temperatures have been increasing in recent decades. IPCC (2007) report mentioned that there is rise in temperature by C in twentieth century and also projected a warming of 0.20C/decade. Regional surface temperature trends may have different warming rates or even cooling trends relating to land cover/land use changes such as urbanization and irrigation. The cause of increased heating in urban area may be from the trapping of the reflected solar radiation by the narrow arrangement of buildings which is ultimately absorbed by the walls of the buildings. Other factors such as increased atmospheric pollutants, production of waste heat from air-conditioning, refrigeration systems and industrial processes also contribute to a higher minimum temperature. One of the most significant consequences of global warming due to increase in greenhouse gases would be an increase in magnitude and frequency of extreme temperature and precipitation events.

3 Record Breaking Heat waves (WMO-2016) 1.Philodi (India) recoreded 51 0 C on 16 May, Pretoria and Johannesburg recorded C& C on 7 January, Mitribah (Kuwait), 54 0 C on 21 July, 2016, 4.Basara (Iraq), C and Delharan (Iran), 53 0 C on 22 July, Objectives (1)To investigate the annual and seasonal trends in temperatue over the country as a whole and in its homogeneous zones. (2)Using the percentile values as a threshold (extreme temperature indices), the hot/cold days as well as hot/cold nights are used to estimate the frequencies of extreme temperature events. (3) To investigate the seasonal and annual trends and variations in (i) frequency and magnitude of extreme rainfall intensity and its contribution to total rainfall (ii) highest rainfall events (iii) frequency of extreme rainfall events and days (iv) frequency of rainfall events and days with daily rainfall above 100 mm and 200 mm in a grid box (1 1 ) over different homogeneous rainfall regions and over the country as a whole.

4 Variation and trends in temperatures over homogeneous temperature regions and India as a whole Location of stations under different subdivisions

5 Present presentation focuses on the trends significant at 5% level in annual, seasonal maximum and minimum temperature and its dependent temperature parameters over India as a whole and over widely spaced 23 stations in different subdivisions over India from 1975 to The daily temperature series for this present study was obtained from India Meteorological Department. Using the percentile values (extreme temperature indices), the number of hot and cold days in daily maximum temperature and number of hot and cold nights in daily minimum temperature were detected for every season and year in the entire period of study. In brief the extreme temperature events are as: Hot days = Days with maximum temperatures above 90 th percentile Cold days = Days with maximum temperatures below 10 th percentile Hot nights = Nights with minimum temperatures above 90 th percentile Cold nights = Nights with minimum temperatures below 10 th percentile.

6 Temperature 0 C Temperature 0 C Temperature 0 C Temperature 0 C Temperature 0 C TRENDS IN TEMPERATURE OVER ALL INDIA MAXIMUM TEMPERATURE Annual mean maximum temperature showed singnificant increasing trend at the rate of C/decade over all India. Increasing trend noticed more than 70% stations but significant increasing trend at 5% level is observed at 39% of the stations. Most sharp increase was noticed in winter season ( C/decade). * Significant at 5% level, ** at 1% level and *** at 0.1% level *** at 0.1% 0.26 level 0 C/Decade** Pre monsoon season Monsoon season C/Decade Post monsoon season C/Decade** Annual Winter season Year C/Decade* Year Year Year C/Decade*** Year Significant trends in seasonal/annual mean maximum temperature ( 0 C/decade) over representative stations

7 Temperature 0 C Temperature 0 C Temperature 0 C Temperature 0 C Temperature 0 C TRENDS IN TEMPERATURE OVER ALL INDIA MINIMUM TEMPERATURE Annual mean minimum temperature showed singnificant positive trend at the rate of C/decade over all India. Positive trend was noticed more than 2/3rd of the statons but significant increasing trend at 5% level is observed at about 50% of the stations. Most sharp rise in night temperature was noticed in winter season ( C/decade). (* Significant at 5% level, ** at 1% level, *** at 0.1% level 13 Winter season C/Decade*** 22 Pre monsoon season C/Decade** Monsoon season C/Decade*** 17 Post monsoon season C/Decade 19.5 Annual C/Decade*** Year Year Year Year Year Significant trends in seasonal/annual mean minimum temperature ( 0 C/decade) over representative stations

8 HIGHEST MAXIMUM TEMPERATURE Mean annual highest maximum temperature over all India showed increasing trend at the rate C/decade (not significant). Season wise all most all the stations (more than 90%) showed positive trend in highest temperature in winter season out of which 50% stations have significant rising trend. Over India as a whole mean highest temperature is increasing significantly at the rate of C/decade during winter season. (* Significant at 5% significant level) Significant trends in seasonal/annual higest maximum temperature ( 0 C/decade) over representative stations

9 LOWEST MINIMUM TEMPERATURE Annual mean lowest minimum temperature showed significant increasing trend at the rate of C/decade over India. Nearly 65% of stations showed rising trends out of which 33% of stations have significant positive trend. Season wise sharp increase was noticed in winter over the country as a whole. (* Significant at 5% significant level) Significant trends in seasonal/annual lowest minimum temperature ( 0 C/decade) over representative stations

10 Trends in Extreme Temperatures Trends in frequency of hot days/decade Annual number of occurrence of hot days in the India is increasing significantly at the rate of 5.5 days/decade. Significant increase in annual frequency of hot days was found about 43% of stations. On seasonal scale, significant increase in hot days was observed in winter, monsoon and post monsoon 2.1 and 1.6 days/decade respectively. (* Significant at 5% significant level). significant trends in seasonal /annual frequency of hot days (number of days/decade) over representative stations

11 Trends in frequency of cold days/decade Annual frequency of cold day over India is decreasing 2.4 days/decade (26% of stations were facing significant decrease in annual frequency of cold days). (* Significant at 5% level). significant trends in seasonal /annual frequency of cold days (number of days/decade) over representative stations

12 Trends in frequency of hot nights/decade More than 60% station mostly in northern and north east India shows significant increasing trends in annual frequency of hot night. On average, 10% night in the year was hot night in the country and increasing significantly at the rate of 12.9 days/decade annually at 5% significance level. Significant increasing trend was observed in all the seasons and largest rate of increase was observed in monsoon and winter season significant trends in seasonal /annual frequency of hot night (number of days/decade) over representative stations

13 Trends in frequency of cold nights/decade Annual frequency in cold night is significantly 9.0 days/decade over the country. Nearly 80% of the total stations facing decline in annual frequency of cold nights (significant decline was observed at about 21% of stations).significant decline was observed in all the seasons over the country as a whole. significant trends in seasonal /annual frequency of cold nights (number of days/decade) over representative stations

14 Variability and Trend in Extreme Rainfall Over India Present study investigated the seasonal and annual trend and variations in the occurrence of extreme rainfall events over different homogeneous regions and India as a whole. Trends and variations are examined on the basis of following parameter (i) frequency and magnitude of extreme rainfall intensity (ERI) (ii) highest rainfall events (iii) frequency of extreme rainfall events and days and its contribution in total rainfall (iv) frequency of rainfall events and days with daily rainfall above 100 mm and 200 mm in a grid box (1 x 1 ) over different rainfall region and India as a whole. Data Daily gridded rainfall data from India Meteorological Department (IMD) available at 1 x1 resolution in the period of has been used to examine trends and variations associated with extreme rainfall events. Methodology On the long term 95 and 99 percentile values of daily total /maximum rainfall considered as a threshold for extreme rainfall intensity / event of category 1 and category 2, trends and variation in above mentioned parameters are analyzed for the period , and Seasonal and annual trend and variability in frequency and intensity of heavy rainfall events are examined for country as a whole and for different homogeneous regions. The Mann Kendall nonparametric test is applied in order to detect trends in different extreme parameter. The magnitude of the trends was estimated using Sen Slope (Sen 1968).

15 Different homogeneous regions under study

16 Maximum daily average rainfall intensity JF=NW(8.4mm), SON=SP(10.8mm) MAM (10.7mm) & JJAS(17.2mm)=NE Significant increasing trend over NW,WP in winter & NC in pre-monsoon Decreasing trend over SP in pre-monsoon (a) (b) Mean of 10 higest rainfall days is higest over SP(29.2mm) & lowest over NW (15.1mm) Intensity increased over SP by 2mm in (c) Contribution of 10 highest rainfall days to annual rainfall is increased by 1% during over WP & SP, decrease is seen over NC & NE regiojns. (d) (a) Daily mean rainfall in a grid box in (i) winter season (blue), (ii) Pre-monsoon season (red), (iii) monsoon season (green), (iv) post monsoon (violet) and (v) annual (orange), (b) Trends in mean daily rainfall in a grid box over the country as a whole, arrow indicate significant trend at 5% significance level during , (c) Mean ten days highest rainfall / grid box over different regions and the country as a whole in the period of (i) (blue), (ii) (red), (iii) (green) indicate % departure in rainfall in a grid box during the period compared to and (d) Same as Fig. (c), but for contribution of highest ten days total rainfall to total rainfall.

17 334.1mm 320mm 348.5mm 257.9mm 236.8mm 285mm 234.9mm 211.4mm 265.7mm maximum change 240.2mm 238.3mm 241mm Minimum change Variations in the generalized extreme value probability distribution function for annual highest rainfall over country and homogeneous regions in a grid box (24 hours) during (a) (left), (b) (middle) and (c) (right). (number shows most probable annual highest rainfall events)

18 195.6mm 180mm 213.1mm 249.8mm 234mm 268.8mm 214.8mm 201.8mm 228.3mm The area under right tail is seen largest increased (increase in magnitude of highest rainfall events) over NW, NC and WP region and least over NE region.

19 Frequency of extreme rainfall days

20 Long term percentile value of daily maximum rainfall (The days having total rainfall more than the 95 & and 99 percentile values are considered as days of extreme rainfall intensity (ERI) ( ). (a)( a

21 Category 1 Category 2 Trends in annual frequency of extreme rainfall days * significant at 5%, ** at 1%, *** at 0.1% 21% days in a year meet with extreme rainfall of category 1 while 4.9% days in a year with category 2. Significant Increasing in annual frequency of category 1 in category 2. Fastest rate of increase can be seen over NC regions for Category 1 and over EP region for category 2.

22 Frequency of extreme rainfall events

23 Category 1 Category 2 Trends in annual frequency of extreme rainfall events, * significant at 5%, ** at 1%, *** at 0.1%. Significant increasing trend in annual frequency of extreme rainfall events over all 11.8 events/decade for category for category 2. Significant increasing ~ 2events/decade over NW,NC,EP for category 1 0.3,0.4,0.7 events/decades over NW,NC,NE for category 2. Comparing the frequency of extreme rainfall events during with ; 20% increase in cateogry 1 and 28% increase in category 2.

24 Annual frequency of daily rainfall above 100mm and 200 mm in any grid box

25 > 100 mm rainfall > 200 mm rainfall Trends in annual frequency of extreme rainfall days (in a grid box in 24 hours), * significant at 5%, **at 1%, *** at 0.1%. Significant increasing trends in number of days were observed in both type of event at the rate of 1.8 (Cat-1)and 1.5(Cat-2) days/decade. Annual frequency of days with rainfall above 100 mm was seen increasing significantly over NC and NE region at the rate of 1.0 and 1.4 days/decade and frequency of days with rainfall above 200 mm exhibited significant positive trend over NW and NC region at the rate of 0.3 and 0.6 days/decade. There was annual increase of 7% in the days with the event of rainfall above 100 mm whereas 54% increase in the days with event of rainfall above 200 mm in compared to observed in a year in the period of as compared to over the

26 >100mm rainfall > 200 mm rainfall Trends in annual frequency of extreme rainfall events (in a grid box in 24 hours), * significant at 5%, ** at 1%, *** at 0.1%. Rainfall events was most significantly increasing at the rate of 13.7 (cat-1) and 3.4(cat-2) events/ decade in the period of mean frequency of rainfall events above 100 mm rainfall were mostly concentrated over NE region (about 74 events in a year), while 61 and 51 number of events were observed over NW and WP regions respectively. Its frequency was lowest over EP region (17). The mean annual frequency of rainfall events above 200 mm rainfall were also mostly populated over NE (6.8 events), NW (4.9 events).

27 Conclusions Annual mean maximum 0 C/decade) and minimum 0 C/decade) temperature over India is observed to be increasing and most of the stations under study reflect significant warming trends in annual mean maximum (39%) and minimum (50%) temperature. Occurance of hot days over India is increasing significantly at the rate of 5.5 days/decade (43% staions) while frequency of cold day is decreasing of 2.4 days/decade (26% of station). Stations in southern India showed significant Sharp decrease in frequency of cold days and increase in hot days. Occurrence of hot nights over the country showed significant increasing days/decade (60% stations mostly in northen India) while occurance of cold night have shown decreasing 9.0 days /decade (21% stations). Daily mean rainfall shows an increasing trend during winter over NW and in premonsoon over NC regions while decreasing trend over SP region in pre-monsoon. Significant incresng trend (2.56days/decade) is observed in the annual frequency of extreme rainfall days under category 1 while significant increasing trend (1.67days/decade) in category 2. Significant increasing trend was found in annual frequency of extreme rainfall events of category 1 and category 11.8 events and 2.5 events/decades over country as a whole.

28 Thanks for Kind attention