Spatiotemporal Variability of Weather Extremes Over Eastern India: Evidences of Ascertained Long Term Trend Persistence and Effective Global Climate Controls

doi:10.21203/rs.3.rs-934391/v1

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Spatiotemporal Variability of Weather Extremes Over Eastern India: Evidences of Ascertained Long Term Trend Persistence and Effective Global Climate Controls

https://doi.org/10.21203/rs.3.rs-934391/v1

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published 07 Feb, 2022

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The present study acknowledged climate variability induced periodic variation in localized extreme weather event occurrences under diverse agro eco-regions of Eastern Himalayas of India during past five decades. The widespread rise in warm nights (TN90p; 0.31-1.67 days year^-1), reduced daily rainfall intensity (SDII) and changes in other weather extremes viz. temperature and precipitation extremes signified clear signals on regional atmospheric warming across eastern India. The agro-ecological regions under extended Bramhaputra valley and coastal belts of south Bengal experienced the most persistent shifts in temperature extremes, while the upper Himalayan range extended from North Bengal to Arunachal Pradesh experienced the steepest decline in average daily rainfall intensity and other absolute quantitative estimates of precipitation extremes over past five decades. Together with El Niño and La Niña events, large scale global atmospheric circulations particularly expansion of warmer Pacific Warm Pool (PWP) and changes in Atlantic Meridional Mode (AMM) contributed the periodic dynamics in weather extreme occurrences from monthly to annual time scale over eastern India. Our findings will be useful for better understanding of regional climatology, designing and successful implantation of location-specific suitable agricultural policies towards climate change adaptation in near future.

Climatology

Temperature

Precipitation

Global teleconnection

Agro-eco region

Eastern India

Table 1a: Spatial distribution of surface weather stations across the six agro-eco regions of eastern and north east India (Source: Mandal et al. 2016)

Sl. no.	Agro-Eco region	Notations	Surface stations
1.	Warm per-humid purvanchal region with red and yellow soils	D3A6 LGP >210 days (Agro eco-region/ AER I8)	Aizawl, Imphal, Cherrapunjee, Shillong, Kohima, Agartala, Kailashar,
.2.	Warm per-humid agro-eco-region with shallow and skeletal red soils	C13-1A6 LGP >210 days (Agro eco-region/ AER 17)	Pasighat, Darjeeling, Gangtok, Kalimpong
.3.	Warm humid to per-humid eco-region with loamy to clayey alluvial soils (Assam and North Bengal plain)	Q8B(A)6 LGP >210 days (Agro eco-region/ AER 16)	Dibrugarh, Chaparmukh, Guwahati, North Lakhimpur, Rangia, Tangla, Tezpur, Coochbehar, Jalpaiguri, Balurghat
.4.	Hot sub-humid agro-eco-region with loamy to clayey alluvial soils (Bengal basin)	O8C5(6) LGP 180-210 days (Agro eco-region/ AER 15)	Alipore, Dumdum, Malda, Uluberia, Burdwan, Berhampore, Shantiniketan, Krishnanagar, Bagati
5.	Hot sub-humid agro-eco-region with red and lateritic soils	J2C5(4) LGP 180-210 days (Agro eco-region/ AER 12)	Midnapore, Purulia
.6.	Hot sub-humid coastal and deltic alluvial soils (Eastern coastal plains)	ST7C(B/A)4-5 LGP 150-210+ days (Agro eco-region/ AER 19)	Contai, Canning, Haldia, Diamond Harbour

(Note: LGP- length of growing period; IMD- India Meteorological Department)

Table 1b: Detailed list of extreme climate indices assessed in the present study.

Notation	Indices	Definition	Unit
TN10p	Cool nights	Percentage of days when TN<10th percentile	Days
TX10p	Cool days	Percentage of days when TX<10th percentile	Days
TN90p	Warm nights	Percentage of days when TN>90th percentile	Days
TX90p	Warm days	Percentage of days when TX>90th percentile	Days
TXx	Max Tmax (warmest day)	Monthly maximum value of daily maximum temperature	ºC
TNx	Max Tmin (warmest night)	Monthly maximum value of daily minimum temperature	ºC
TXn	Min Tmax (coldest day)	Monthly minimum value of daily maximum temperature	ºC
TNn	Min Tmin (coldest night)	Monthly minimum value of daily minimum temperature	ºC
DTR	Diurnal temperature range	Monthly mean difference between TX and TN	ºC
SU25	Summer days	Annual count when TX(daily maximum)>25ºC	Days
TR20	Tropical nights	Annual count when TN(daily minimum)>20ºC	Days
WSDI	Warm spell duration indicator	Annual count of days with at least 6 consecutive days when TX>90th percentile	Days
CSDI	Cold spell duration indicator	Annual count of days with at least 6 consecutive days when TN<10th percentile	Days
RX1	Max 1-day precipitation amount	Monthly maximum 1-day precipitation	mm
Rx5	Max 5-day precipitation amount	Monthly maximum consecutive 5-day precipitation	mm
SDII	Simple daily intensity index	Annual total precipitation divided by the number of wet days (defined as PRCP>=2.5 mm) in the year	mm/day
R95p	Very wet days	Annual total PRCP when RR>95th percentile	mm
R99p	Extremely wet days	Annual total PRCP when RR>99th percentile	mm
PRCPTOT	Annual total wet-day precipitation	Annual total PRCP in wet days (RR>=1mm)	mm
CDD	Consecutive dry days	Maximum number of consecutive days with RR<1mm	Days
CWD	Consecutive wet days	Maximum number of consecutive days with RR>=1mm	Days
R10	Number of heavy precipitation days	Annual count of days when PRCP>=10mm	Days
R25	Number of very heavy precipitation days	Annual count of days when PRCP>=25mm	Days
R50	Number of extreme heavy precipitation days	Annual count of days when PRCP>=50mm	Days

Table 2: Rank based factor loading with 10% threshold values of identified global teleconnection indices in rotated principal component (PCs) matrix accounting 89.58% cumulative variance (Note: % of variance accounted in the parenthesis for each PC)

Sl. no.	PC 1 (25.86)	PC 2 (23.89)	PC 3 (8.53)	PC 4 (7.30)	PC 5 (5.25)	PC 6 (5.11)	PC 7 (5.01)	PC 8 (4.55)	PC 9 (4.08)
1.	ONI	PWP	NAO	NP	EPNP	WP	AMM	TNI	QBO
2.	Nino3.4	GlobalTa	NAO_J	PNAP	EPO	WPO	CI
3.	BEST2	Nhta		PNA		Sahel	TSA
4.	EOFPAC	LOTINH
5.	Nino3	Global LOTI
6.	TPIIPO
7.	MEI2
8.	SOI

Table 3: Significant canonical correlation observed between global teleconnection and weather extreme event time series over Eastern India on variable time scale

Time scale	Eigenvalues	Corresponding Variability accounted (%)	Corresponding Cumulative Variability (%)	Canonical correlations co-efficient	Wilks' Lambda	P value
El Nino events	0.768	39.145	39.145	0.876	0.058	< 0.0001
	0.406	20.724	59.869	0.638	0.250	< 0.0001
	0.251	12.806	72.675	0.501	0.421	< 0.0001
	0.199	10.160	82.835	0.446	0.562	0.0086
La Nina events	0.633	31.901	31.901	0.796	0.067	< 0.0001
	0.527	26.535	58.436	0.726	0.183	< 0.0001
	0.356	17.944	76.380	0.597	0.386	< 0.0001
	0.229	11.542	87.922	0.479	0.605	0.0091
Monthly	0.627	50.571	50.571	0.792	0.182	< 0.0001
	0.381	30.691	81.261	0.617	0.487	< 0.0001
	0.092	7.429	88.690	0.304	0.787	< 0.0001
	0.041	3.304	91.994	0.202	0.867	0.008
	0.039	3.108	95.102	0.196	0.904	0.032
Annual	0.9631	21.411	21.411	0.960	0.001	0.0016

Table 4: Association between weather extreme events in eastern India with Global teleconnection indices at (a) annual and (b) monthly time scale

(a) Annual extremes	ONI		PWP		NAO		NP		EPNP		WP		AMM		TNI		QBO
(a) Annual extremes	r0	r1	r0	r1	r0	r1	r0	r1	r0	r1	r0	r1	r0	r1	r0	r1	r0	r1
TN10p	-	-	2.64	11.96	-	-	-	-	-	-	-	-	9.56	14.68	-	-	-	-
TX10p	-	-	2.52	27.00	-	-	-	-	-	-	-	-	6.91	22.64	-	-	-	-
TN90p	6.00	21.78	2.44	15.62	-	-	-	-	-	-	-	-	6.05	19.40	-	-	-	-
TX90p	-	-	2.09	18.37	-	-	-	-	-	-	-	-	7.13	20.72	-	-	-	-
DTR	-	-	7.19	19.05	-	-	-	-	-	-	-	-	3.91	14.04	-	-	-	-
SU20	-	-	2.35	14.28	-	-	-	-	-	-	-	-	7.76	23.70	-	-	-	-
TR20	6.44	24.40	2.59	8.40	-	-	-	-	-	-	-	-	7.86	16.02	-	-	-	-
WSDI	-	-	2.28	21.21	-	-	-	-	-	-	-	-	6.99	17.83	-	-	-	-
ZRD	-	-	3.76	11.55	-	-	-	-	7.67	24.56	-	-	7.90	21.35	-	-	-	-
SDII	-	-	2.59	17.84	-	-	-	-	10.10	13.02	-	-	7.59	37.19	-	-	-	-
R95p	-	-	2.68	27.25	-	-	-	-	10.54	12.80	-	-	7.84	17.04	-	-	-	-
R99p	-	-	2.63	24.01	-	-	-	-	10.12	11.56	-	-	7.88	36.45	-	-	-	-
PRCPTOT	-	-	2.11	38.20	-	-	-	-	7.81	23.50	-	-	6.90	36.14	-	-	-	-
CDD	-	-	-	-	-	-	-	-	6.56	9.99	-	-	4.62	23.82	-	-	-	-
CWD	-	-	-	-	-	-	-	-	6.61	30.78	-	-	7.13	18.83	-	-	-	-
R10	-	-	2.82	22.06	-	-	-	-	6.23	19.34	-	-	6.56	24.24	-	-	-	-
R25	-	-	2.99	23.38	-	-	-	-	5.41	19.17	-	-	6.00	26.10	-	-	-	-
R50	-	-	2.96	23.20	-	-	-	-	7.83	28.59	-	-	6.14	17.51	-	-	-	-

(b) Monthly extremes	AER 18		AER 17		AER 16		AER 15		AER 12		AER 19
(b) Monthly extremes	r0	r1	r0	r1	r0	r1	r0	r1	r0	r1	r0	r1
ONI
TN10p	5.14	70.27	5.26	60.19	5.59	114.16	0.00	109.57	5.38	49.04	5.05	48.22
TX10p	5.32	88.76	5.41	105.03	5.03	133.26	4.35	90.19	4.98	121.59	4.99	119.97
TN90p	5.41	86.07	5.09	106.53	5.20	98.63	0.00	139.79	5.09	124.81	4.93	94.99
TX90p	5.24	78.59	5.06	65.97	5.27	90.26	4.69	113.75	5.22	137.38	5.22	85.23
TXx	5.22	91.64	5.32	106.71	5.26	139.64	4.63	146.18	5.23	178.37	5.20	185.06
TXn	5.20	108.63	5.32	108.81	5.26	93.26	4.85	112.98	5.21	130.16	5.18	118.15
TNx	5.26	133.36	5.25	129.12	5.21	140.32	5.28	137.16	5.36	164.86	5.27	186.31
TNn	5.22	123.96	5.27	93.86	5.24	105.13	5.26	96.26	5.22	93.92	5.23	108.49
DTR	5.21	143.49	5.22	78.48	5.26	152.43	5.27	154.46	5.30	114.41	5.23	170.19
ZRD	5.09	110.86	4.45	123.48	0.01	128.40	0.01	137.18	5.18	98.31	5.18	119.20
RX1	5.14	101.17	5.22	105.43	5.16	105.92	5.19	113.37	5.25	123.60	5.27	107.44
RX5	5.12	92.01	5.21	98.89	5.15	101.32	5.18	119.91	5.27	110.69	5.17	100.71
PWP
TN10p	4.24	74.14	4.62	59.69	4.48	142.88	4.51	130.14	4.61	44.03	4.53	48.31
TX10p	4.57	92.02	4.57	94.60	4.08	135.78	7.59	102.68	4.21	120.53	4.53	119.17
TN90p	4.02	95.75	4.18	137.37	4.23	120.02	4.20	142.30	4.57	112.92	4.01	129.08
TX90p	4.56	95.52	4.11	60.76	4.92	96.01	5.22	113.05	4.68	135.01	4.59	105.54
TXx	4.57	95.30	4.64	108.83	4.58	139.42	5.23	145.14	4.58	178.46	4.55	187.79
TXn	4.73	109.85	4.68	108.85	4.63	93.47	4.63	116.06	4.56	132.11	4.75	119.60
TNx	4.58	139.48	4.62	129.05	4.61	141.97	4.64	138.31	4.57	165.10	4.54	187.43
TNn	4.62	124.18	4.65	92.67	4.63	106.17	4.60	97.91	4.55	94.75	4.57	108.14
DTR	4.65	144.65	4.56	84.30	4.49	152.31	4.54	159.63	4.57	111.98	4.47	169.33
ZRD	4.56	111.82	0.01	135.81	5.15	114.15	5.17	128.27	4.55	109.85	4.51	118.31
RX1	4.63	101.17	4.81	106.24	4.61	106.58	4.61	114.02	4.66	124.83	4.63	108.65
RX5	4.65	92.61	4.79	98.98	4.64	102.93	4.60	119.83	4.56	110.73	4.56	101.92
AMM
TN10p	0.01	70.72	0.01	67.15	0.01	142.87	5.00	113.06	0.01	54.41	0.02	58.78
TX10p	0.01	101.22	0.01	112.33	0.01	146.68	0.01	135.36	0.01	133.73	0.01	147.68
TN90p	0.01	93.19	0.01	135.99	0.01	157.89	4.62	108.47	0.00	140.91	0.01	126.12
TX90p	0.01	109.06	0.02	80.34	0.01	106.08	0.01	133.84	0.01	149.79	0.01	121.69
TXx	0.01	106.84	0.01	119.23	0.01	159.17	0.01	150.45	0.01	193.85	0.01	208.29
TXn	0.01	120.67	0.01	119.57	0.02	102.58	0.01	98.71	0.01	143.90	0.01	131.25
TNx	0.01	145.79	0.01	144.32	0.01	158.46	0.01	150.09	0.01	178.86	0.01	209.94
TNn	0.01	143.50	0.01	101.70	0.01	119.28	0.01	105.20	0.01	106.84	0.02	122.01
DTR	0.01	161.87	0.01	102.31	0.01	170.14	0.01	183.89	0.02	132.99	0.01	188.24
ZRD	0.01	124.34	5.11	123.03	4.47	114.55	4.58	127.95	0.01	122.44	0.01	129.46
RX1	0.01	111.49	0.01	114.86	0.01	117.00	0.01	121.67	0.01	135.47	0.01	121.44
RX5	0.01	103.16	0.01	108.57	0.01	112.92	0.01	128.77	0.01	118.63	0.01	114.88

Table 5: Association between weather extreme events over eastern India with rising global greenhouse gas emission (CH₄ and CO₂), outgoing longwave radition (OLR), sunspot activity (SSP) and solar flux (SF) during the study period.

Extreme indices	CH₄		CO₂		OLR		SSP		SF
Extreme indices	r0	r1	r0	r1	r0	r1	r0	r1	r0	r1
TN10p	0.70	17.12	7.93	12.37	6.75	17.91	-	-	-	-
TX10p	0.77	16.68	7.59	18.68	6.87	17.18	-	-	-	-
TN90p	0.91	21.42	6.35	14.94	9.66	13.67	7.73	22.62	8.15	17.47
TX90p	1.56	12.10	7.30	15.13	9.10	13.31	-	-	-	-
DTR	0.91	13.72	4.31	9.28	2.94	20.50	4.64	26.49	4.79	23.95
SU25	0.96	17.41	7.40	20.17	5.06	13.00	-	-	-	-
TR20	0.39	22.49	8.76	9.02	7.33	16.40	-	-	-	-
WSDI	1.03	17.13	6.66	25.42	8.17	19.11	-	-	-	-
CSDI	0.86	14.24	6.63	19.83	11.89	14.05	-	-	-	-
ZRD	0.49	12.57	10.47	13.75	7.47	15.86	-	-	-	-
SDII	0.68	18.70	-	-	9.31	11.15	-	-	-	-
R95p	0.67	21.54	-	-	10.57	14.63	-	-	-	-
R99p	0.78	17.36	-	-	9.26	13.83	-	-	-	-
PRCPTOT	1.00	22.12	6.84	42.04	-	-	-	-	-	-
CDD	0.68	19.62	6.07	25.59	-	-	-	-	-	-
CWD	1.09	10.19	5.74	15.71	-	-	-	-	-	-
R10	0.74	18.27	4.33	40.61	-	-	-	-	-	-
R25	0.68	15.20	4.54	30.79	-	-	-	-	-	-
R50	1.02	22.19	7.56	35.01	-	-	-	-	-	-

Note:

1. Threshold values of either r0 = 6.5 (p< 0.10); 8.18 (p<0.05); 11.65 (p<0.01) or r1 = 12.91 (p< 0.10); 14.9 (p<0.05); 19.19 (p<0.01) were statistically significant.

2. We have omitted non-significant values of r0 & r1 pairs in table 4 and table 5 in order to increase readability of the manuscript.

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