Isotopic characteristics of Indian precipitation - BES journal

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parts of the country during the winter season. ...... inates in the western Himalayan during the winters causing different ..... R. O'Neil, and R. Kaplan, Geochem.
WATER RESOURCES RESEARCH, VOL. 46, W12548, doi:10.1029/2009WR008532, 2010

Isotopic characteristics of Indian precipitation Bhishm Kumar,1 S. P. Rai,1 U. Saravana Kumar,2 S. K. Verma,1 Pankaj Garg,1 S. V. Vijaya Kumar,1 Rahul Jaiswal,1 B. K. Purendra,1 S. R. Kumar,1 and N. G. Pande1 Received 19 August 2009; revised 22 June 2010; accepted 6 August 2010; published 22 December 2010.

Hydrogen (2H/1H) and oxygen (18O/16O) isotopic ratios were measured in precipitation (900 samples) collected from several locations in India during the period 2003–2006 (12 locations in 2003 and 18 locations in 2004–2006). The amount of rainfall along with air temperature and humidity were also measured. The meteoric water line developed for India using isotopic data of precipitation samples, namely, d 2H = 7.93 (±0.06) × d 18O + 9.94(±0.51) (n = 272, r2 = 0.98), differs slightly from the global meteoric water line. Regional meteoric water lines were developed for several Indian regions (i.e., northern and southern regions of India, western Himalayas) and found to be different from each other (southern Indian meteoric water line, slope is 7.82, intercept or D excess is 10.23; northern Indian meteoric water line, slope is 8.15, intercept is 9.55) which is attributed to differences in their geographic and meteorological conditions and their associated atmospheric processes (i.e., ambient temperature, humidity, organ, and source of vapor masses). The local meteoric water lines developed for a number of locations show wide variations in the slope and intercept. These variations are due to different vapor sources such as the northeast (NE) monsoon that originates in the Bay of Bengal; the southwest monsoon (SW) that originates in the Arabian Sea; a mixture of NE and SW monsoons; retreat of NE and SW monsoons and western disturbances that originate in the Mediterranean Sea. The altitude effect in the isotopic composition of precipitation estimated for western Himalayan region also varies from month to month. [1]

Citation: Kumar, B., S. P. Rai, U. Saravana Kumar, S. K. Verma, P. Garg, S. V. Vijaya Kumar, R. Jaiswal, B. K. Purendra, S. R. Kumar, and N. G. Pande (2010), Isotopic characteristics of Indian precipitation, Water Resour. Res., 46, W12548, doi:10.1029/2009WR008532.

1. Introduction [2] The stable isotopes of hydrogen and oxygen can be used to characterize the precipitation and other sources of water in a region or area. Globally, the stable isotopic compositions of precipitation have been explained in the form of a global meteoric waterline (GMWL) by Craig [1961]. The GMWL represents the variation of d2H with respect to d18O in precipitation and can be used to identify the source of water, mixing, and other hydrological processes. The meteoric waterline is represented in its generalized form as d2H = A × d18O + d, where A represents the slope and d represents the intercept or D excess (2H excess). The International Atomic Energy Agency (IAEA) of Vienna, Austria, in collaboration with the World Meteorological Organization (WMO), established the Global Network of Isotopes in Precipitation (GNIP) under which water samples are collected to monitor the isotopic composition (d2H, d 18O) of precipitation. The data produced from this network form an

important asset to isotope hydrology. (These are available at http://isohis.iaea.org.) The regression line for the long‐term average of d2H and d 18O [Rozanski et al., 1993] data measured for precipitation at 219 stations under WMO‐IAEA network adds some precision to the Craig line: 2 H ¼ 8:17ð0:07Þ  18 O þ 11:27ð0:65Þ;

where Vienna standard mean ocean water (VSMOW) was used as the standard for the isotopic measurements. Kumar et al. [1982] found the regional meteoric waterline for lower Maner Basin in the state of Andhra Pradesh in southern India, as 2 H ¼ 7:6ð0:4Þ  18 O þ 6:3ð2:7Þ ðn ¼ 26Þ:

ð2Þ

[3] Datta et al. [1991] established similar LMWL for Delhi using the annual weighted mean values for the period 1961–1982 which is similar to that of Das et al. [1988] reported for the period 1961–1978.

1 Hydrological Investigations Division, National Institute of Hydrology, Roorkee, India. 2 Isotope Hydrology Section, Isotope Applications Division, Bhabha Atomic Research Centre, Mumbai, India.

Copyright 2010 by the American Geophysical Union. 0043‐1397/10/2009WR008532

ð1Þ

 2 H ¼ 8:39  18 O þ 11:41 ðr2 ¼ 0:95 :

ð3Þ

[4] Datta et al. [1991] also established LMWL for Delhi using the monthly (equation (4)) and composite weighted mean monthly (equation (5)) isotopic data of monsoon

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months for rainfall less than 30 mm for the period from 1961 to 1978.  2 H ¼ 6:88  18 O þ 1:61 ðr2 ¼ 0:90

ð4Þ

 2 H ¼ 6:82  18 O þ 0:68 ðr2 ¼ 0:83

ð5Þ

Mukherjee and Chandrasekharan [1993] reported LMWL for Delhi (equation (6)) and Mumbai (equation (7)) using monthly isotopic composition of precipitation for the period 1961–1966 and 1973–1977 as given below  2 H ¼ 6:80  18 O þ 1:25 ðn ¼ 44; r2 ¼ 0:96

ð6Þ

 2 H ¼ 8:16  18 O þ 8:84 ðn ¼ 43; r2 ¼ 0:81 :

ð7Þ

The authors attribute the differences in slope and intercept between the two stations (Delhi, Mumbai) to higher evaporation in Delhi which probably is corroborated by equation (5). [5] There are different types of effects like continental, altitude, seasonal, and amount effect which the isotopic composition may vary from place to place and at different times. But these effects once established for a region may not change much (except amount effect) unless climatic and hydrological regimes change considerably. In order to understand the isotopic characterization of precipitation, many other investigators like Dansgaard [1964]; Yurtsever [1975]; Gat [1980]; Gat and Gonfiantini [1981]; Kumar et al. [1982]; Rozanski [1985]; Fritz et al. [1987]; Nativ and Riggio [1989]; Gedzelman and Lawrence [1990]; Krishnamurthy and Bhattacharya [1991]; Rozanski et al. [1991, 1993]; Friedman et al. [1992]; Simpkins [1995]; Takle [1994]; Amundson et al. [1996]; Gat [1996]; Araguás‐Araguás et al. [1998]; Bhattacharya et al. [2003]; Deshpande et al. [2003]; IAEA/ WMO (Global Network of Isotopes in Precipitation Database, http://isohis.iaea.org, 2003); and Saravana Kumar et al. [2008, 2009] have studied d2H and d18O variations in precipitation and also developed meteoric waterlines in many cases for different parts of the world. [6] Reasonably long data series of isotopes in precipitation exist only for one Indian station, namely, New Delhi. Other Indian stations (Bombay, Kozikhode, Shillong, Hyderabad) have only records for short periods. Therefore, 2 to 3 years of isotopic data have been used in this study to understand the isotopic characteristics of precipitation in different parts of India by establishing meteoric waterlines.

2. Sources of Precipitation [7] The two principal sources of oceanic vapor to the Indian subcontinent are the Arabian Sea (AS) and the Bay of Bengal (BOB). During the SW monsoon (June–September), the west coast of India receives vapor from the Arabian Sea (AS) and is orographically uplifted by the Western Ghats. This section of the Indian SW monsoon is called the AS branch of the monsoon. Because of “rainout,” the vapor content of the AS Branch of monsoon is considerably reduced by the time they reach the middle of the Peninsular India [Rajan, 1988] and cross over the east coast of India. In the BOB, the monsoon current then takes a southeasterly turn entering the Indo‐Gangetic plains after replenishing vapor from the BOB. This section of the Indian SW monsoon is called the BOB branch [Das, 2005] and gives rainfall to the northeastern region of India [Rao, 1976].

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However, certain regions in the northern part of Indian subcontinent receive vapor both from AS and BOB and contribute to rainfall during SW summer monsoon. [8] In addition, the western disturbances that originate in the Mediterranean Sea are responsible for rainfall in many parts of the country during the winter season. These different sources of precipitation have different isotopic composition of precipitation, e.g., the surface waters of Arabian Sea and Bay of Bengal are reported to have mean d18O values of +0.6 ‰ and −0.5 ‰, respectively [Delaygue et al., 2001]. Also, because of a large influx of monsoon runoff from Himalayan rivers, seasonal changes in the isotopic composition of BOB surface water is expected similar to large seasonal surface water salinity changes. This seasonal change in the isotopic composition of surface waters of BOB is expected to lead to different imprinting of the seasonal vapor influx which in turn will transfer to all other components, namely, rainfall, stream flow, soil moisture, and surface and groundwater reservoirs.

3. Experiment 3.1. Sampling Procedure [9] The precipitation sampling was initiated in the year 2003. Precipitation samples, daily during the monsoon and monthly integrated during the other months, were collected from 12 selected locations distributed in different parts of the country using standard procedures [Clark and Fritz, 1997]. The sample collection sites (Figure 1) were increased to 18 in the year 2004–2005 and the western Himalayan region was also included. About 900 precipitation samples were collected during the study. The samples were stored at 10°C in double‐capped plastic bottles to avoid evaporation prior to isotopic analysis. The physicochemical parameters of samples (temperature, electrical conductivity, pH, etc.) were measured on site. The rainfall amount along with air temperature and humidity were also measured. 3.2. Isotopic Analyses [10] The isotopic analyses (d2H, d18O) of about 90% of the water samples were carried out at the Nuclear Hydrology Laboratory of the National Institute of Hydrology (NIH), Roorkee, using Dual Inlet Isotope Ratio Mass Spectrometer (DIIRMS), mostly for d2H measurements, and Continuous Flow Isotope Ratio Mass Spectrometer (CFIRMS), mostly for d18O measurements, installed during the year 2004, and the remaining samples were measured at the Isotope Hydrology Laboratory of IAEA, Vienna. The d 2H and d 18O were measured by Pt–H2 and CO2 equilibration methods, respectively, following the standard procedure [Epstein and Mayeda, 1953; Brenninkmeijer and Morrison, 1987]. To determine d2H and d18O, a three‐point calibration equation was used with the isotopic water standards VSMOW, GISP, and standard light arctic precipitation obtained from the IAEA (precision is ±1.0‰ and ±0.1‰ for d 2H and d 18O, respectively). Due care was taken for having isotopic analytical results of water samples analyzed with CFIRMS and DIIRMS comparable using the measured values of d 18O secondary standards with DIIRMS.

4. Results and Discussion [11] The data of d2H and d18O for all precipitation samples collected from different locations are given in Table 1 while

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Figure 1. Location map of sample collection sites.

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Table 1. The d 2H and d 18O Results of Precipitation of Various Stations in India Rainfall (mm)

Temperature (°C)

Sep 2003 Oct 2003 Nov 2003 Dec 2003 Jan 2004 Jul 2003 Aug 2003 Sep 2003 Oct 2003 Jan 2004 Apr 2004 May 2004 Jun 2004 Jul 2004 Aug 2004 Sep 2004 Oct 2004 Nov 2004 Apr 2005

5.6 26.5 14.0 69.4 34.3 90.4 129 51.1 10.0 28.8 105.3 241.5 293.1 204.7

30.8 30.9 31.5 28.9 27.4 30.6 29.7 29.9 29.8 30.3 29.7 28.0 26.2

Jul 2003 Aug 2003 Sep 2003 Oct 2003 Dec 2003 Jan 2004 Feb 2004 May 2004 Jun 2004 Jul 2004 Aug 2004 Sep 2004 Oct 2004 Jan 2005 Apr 2005 May 2005 Jul 2005 Aug 2005 Sep 2005 Oct 2005 Nov 2005 Apr 2006 May 2006 Jun 2006 Jul 2006 Aug 2006 Sep 2006

255.6 103.2 157.2 322.4 77.0 6.2 3.0 72.9 106.8 183.7 227.3 128.9 272.6 1.2 5.4 38.4 137.8 138.6 434.5 610.9 12.8 77.8 21.8 107.0 73.4 248.5 203.6

28.9 30.1 30.5 28.9 25.1 25.0 26.7 33.2 31.4 29.7 29.6 29.5 28.0 24.1 30.4 31.8 28.1 28.8 27.5 26.8 24.5 30.7 31.2 31.7 30.1 28.7 28.8

Aug 2003 Sep 2003 Oct 2003 Nov 2003 Jun 2004 Jul 2004 Aug 2004 Sep 2004 Oct 2004 Nov 2004 Sep 2005 Oct 2005

164.2 62.6 121.1 41.4 420.1 159.9 530.3 79.5 34.2 19.5 225.2 120.1

23.7 23.8 24.5 24.1 24.1 23.6 22.6 23.7 24.0 23.7 23.3 23.8

Jul 2003 Aug 2003 Sep 2003 Oct 2003 Jan 2004 Mar 2004 May 2004 Jun 2004 Jul 2004

80.3 124.5 100.5 183.2 10.2 9.4 152.8 73.2 142.2

24.8 24.2 24.1 23.8 21.8 26.3 25.1 24.3 23.7

Humidity (%)

pH

Tharamani; 12°59′19″N; 80°15′28″E; 7 m msl a 6.3 6.5 7.9 7.7 7.3 Tirunelveli; 08°43′40″N; 77°43′06″E; 4 m msl a 50.0 7.5 49.5 ‐ 45.5 ‐ 62.0 8.0 65.5 8.0 60.0 7.8 58.5 7.2 55.0 7.8 53.0 8.0 51.0 ‐ 53.5 6.8 67.0 7.2 74.5 7.6 8.0 Kakinada; 17°01′16″N; 82°15′24″E; 8 m msl a 88.5 6.7 86.3 6.7 83.9 7.3 88.3 8.2 87.1 7.2 87.3 8.0 87.9 7.8 85.7 7.0 85.5 7.0 91.3 7.1 87.1 6.3 92.6 6.5 93.8 6.5 92.0 ‐ 85.9 ‐ 81.7 ‐ 90.5 ‐ 92.9 ‐ 96.1 ‐ 94.5 8.5 87.6 10.4 90.0 7 90.9 ‐ 86.1 7.5 86.1 8.8 96.0 8.3 95.9 7.8 Belgaum; 15°52′50″N; 74°29′36″E; 747 m msl a 84.0 7.5 80.5 7.4 69.5 7.6 51.0 7.7 82.0 ‐ 84.0 7.0 87.0 ‐ 81.5 7.5 66.5 7.9 51.0 7.4 88.5 7.6 72.0 7.7 Banglore; 12°58′18″N; 77°35′39″E; 897 m msl a 74.5 6.6 75.0 7.2 68.0 7.3 75.0 4.4 60.5 4.1 43.0 4.0 74.5 6.5 72.5 7.2 75.5 7.2

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EC (mS cm−1)

d 2H (‰)

d 18O (‰)

61 78 47 70 117

−12.4 −75.6 −75.9 ‐ −2.0

−3.0 −11.1 −10.8 −4.5 −2.0

1632 ‐ ‐ 109 66 1707 88 127 164 ‐ 65 78 1927 88

−15.4 −1.1 −37.5 −16.1 −14.3 −16.8 −16.2 −17.7 −17.1 −13.5 −4.8 −26.2 ‐ ‐

−3.0 −0.4 −5.7 −3.1 −3.0 −3.1 −3.0 −3.2 −2.9 −2.7 −2.1 −4.7 ‐ ‐

46 64 56 91 83 581 429 51 42 44 25 46 33 ‐ ‐ ‐ ‐ ‐ ‐ 125 218 100 ‐ 60 43 34 47

−20.8 −17.4 −13.2 −52.9 −45.8 −27.2 −4.0 −40.7 −16.0 +0.1 −16.0 −20.6 −62.1 +0.9 ‐ −29.2 −14.2 +5.1 −63.4 −55.6 −49.4 −37.4 +14.1 +12.1 −3.91 −16.2 −66.2

−3.6 −3.0 −2.8 −8.1 −7.2 −5.8 −2.2 −6.6 −3.2 −1.3 −4.0 −4.3 −9.3 −2.1 −5.6 −5.1 −2.6 −0.2 −8.6 −8.5 −7.9 ‐ ‐ ‐ −1.5 −3.2 −9.0

140 133 139 151 ‐ 48 ‐ 150 138 145 152 141

+10.0 +12.2 −18.3 −4.1 +7.7 +13.9 +9.1 −20.7 −10.0 −21.6 −18.7 −63.2

+0.3 +1.0 −3.8 −1.2 −1.5 −0.8 −1.2 −4.0 −2.3 −4.4 −3.4 −9.4

42 200 162 23 140 134 29 124 27

−25.3 −2.7 −3.4 −29.9 +11.4 ‐ −94.8 −1.6 −16.6

−4.3 −1.6 −1.6 −5.3 −0.2 −8.7 −13.3 −1.8 −4.1

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Table 1. (continued) Rainfall (mm)

Temperature (°C)

Aug 2004 Sep 2004 Oct 2004 Nov 2004

55.4 290.4 193.2 16

23.6 23.6 23.4 21.8

Jul 2004 Aug 2004 Sep 2004 Oct 2004 Jun 2005 Jul 2005 Aug 2005 Sep 2005 Oct 2005 Jul 2006 Aug 2006 Sep 2006 Oct 2006

185.1 277.1 274.2 260.9 160.9 288.3 227.6 237.6 451.1 627.3 292.4 308.3 244.3

28.2 28.0 27.3 25.9 30.8 27.9 28.3 28.4 25.9 27.6 27.5 27.7 26.3

Jul 2003 Aug 2003 Sep 2003 Mar 2005 Apr 2005 May 2005 Jun 2005 Jul 2005 Aug 2005 Sep 2005 Oct 2005 Aug 2003 Sep 2003 Oct 2003 Oct 2004 Aug 2005 Oct 2005

184.0 139.4 131.0 6.4 190.8 38.9

30.1 29.5 26.3 26.6 30.2 26.8

Jul 2003 Aug 2003 Sep 2003 Dec 2003 Jan 2004 May 2004 Jun 2004 Jul 2004 Aug 2004 Sep 2004 Jan 2005 Mar 2005 Jun 2005 Jul 2005 Aug 2005 Mar 2006 May 2006 Jun 2006

248.9 293.7 314.6 7.7 37.5 42.0 316.9 173.2 542.5 126.8 11.4 44.8 201.1 1203.7 124.9 64.0 39.2 117.0

27.5 29.7 26.2 20.5 18.1 32.8 30.0 28.2 25.1 27.6 17.7 26.5 33.3 26.6 26.1 24.5 39.7 31.5

Jul 2003 Aug 2003 Sep 2003 Jun 2004 Jul 2004 Aug 2004 Sep 2004 Oct 2004

73.5 165.0 348.0 245.0 175.0 125.0 200.0 48.0

30.4 30.0 28.6 31.2 ‐ 30.0 29.8 25.8

Jul 2003 Aug 2003 Sep 2003 Oct 2003 Nov 2003 Dec 2003

402.2 491.6 151.7 3.4 28.6 29.6

29.5 29.4 28.2 24.8 19.5 15.3

Humidity (%)

pH

74.0 7.2 76.0 7.3 75.5 7.1 71.0 7.4 Kolkata; 22°47′52″N; 88°22′18″E; 6 m msl a 82.5 ‐ 85.5 8.0 85.0 6.7 78.5 7.0 75.0 ‐ 84.0 ‐ 84.5 ‐ 84.5 ‐ 86.0 ‐ 83.5 ‐ 84.5 ‐ 84.0 ‐ 79.5 ‐ Guwahati; 26°11′27″N; 91°47′43″E; 54 m msl a ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ Patna; 25°34′25″N; 85°04′13″E; 60 m msl a 78.5 6.9 80.0 7.0 76.0 6.8 72.5 7.0 ‐ ‐ Sagar; 23°49′34″N; 78°45′45″E; 551 m msl a 87.8 8.5 88.7 ‐ 88.4 6.7 55.5 7.4 62.0 7.2 34.5 7.4 60.0 7.5 77.0 7.4 90.5 7.5 72.0 7.4 64.0 ‐ 45.5 ‐ 43.5 ‐ 86.5 ‐ 80.5 ‐ ‐ ‐ ‐ Lucknow; 26°52′29″N; 80°56′20″E; 128 m msl a 81.0 6.7 85.0 7.5 88.0 7.2 64.5 7.3 81.5 7.3 83.5 7.5 77.0 7.8 73.0 7.6 Jammu; 32°41′33″N; 74°50′46″E; 367 m msl a 77.0 8.0 79.5 7.4 75.5 6.7 64.0 ‐ 67.0 7.3 76.0 7.4

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EC (mS cm−1)

d 2H (‰)

d 18O (‰)

66 14 54 56

‐ −22.6 −19.9 −3.7

−0.1 −4.8 −5.0 −1.4

‐ 431 48 632 ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐

−67.9 −42.1 −39.5 −77.8 −46.1 −48.0 −37.0 −72.0 ‐ −60.2 −46.3 −61.9 −58.0

−9 −6.4 −5.8 −11.0 −7.0 −7.4 −6.3 −8.4 −10.0 −7.9 −6.6 −8.2 −7.6

‐ ‐

−58.3 −64.3

−8.4 −8.9

‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐

+3.6 +36.3 +37.3 −76.9 −62.4 −65.6 −65.6 −66.1

−0.2 +4.2 +4.0 −9.4 −7.5 −8.0 −8.3 −8.2

50 58 42 52 ‐ ‐

−56.8 −47.7 −69.1 ‐ −94.3 −128.2

−7.62 −6.52 −10.1 ‐ −11.7 −17.1

155 ‐ 27 184 110 90 81 30 46 18 ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐

−32.8 −35.9 −58.4 −15.3 ‐ −37.3 −71.0 −24.0 −74.1 −52.0 +13.2 +16.5 −67.0 −27.0 +7.8 −31.6 −6.3 −31.9

−5.3 −6.0 −8.8 −2.4 −3.7 −5.2 −9.5 −4.0 −10.3 −7.6 +1.1 −0.1 −10.0 −4.2 0 ‐ ‐ ‐

108 248 48 68 59 66 107 51

−75.0 −71.7 −69.1 ‐ −45.0 −56.5 −45.4 −22.8

−10.7 −10.3 −9.7 −2.4 −6.4 −7.5 −6.3 −4.4

212 78 101 ‐ 228 137

−36.1 −32.7 −27.1 ‐ ‐ +0.8

−6.1 −5.7 −4.7 ‐ −2.6 −1.2

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Table 1. (continued)

Jan 2004 Feb 2004 Apr 2004 May 2004 Jun 2004 Jul 2004 Aug 2004 Sep 2004 Oct 2004 Nov 2004 Dec 2004 Jan 2005 Feb 2005 Mar 2005 Apr 2005 May 2005 Jun 2005 Jul 2005 Aug 2005 Sep 2005 Jan 2006 Feb 2006 Mar 2006 Jun 2006 Jul 2006 Aug 2006 Sep 2006 Jul 2003 Aug 2003 Sep 2003 Jan 2004 Feb 2004 Mar 2004 Apr 2004 May 2004 Jun 2004 Jul 2004 Aug 2004 Sep 2004 Oct 2004 Jul 2005 Aug 2005 Sep 2005 Jul 2006 Aug 2006 Sep 2006 Oct 2006 May 2004 Jun 2004 Jul 2004 Aug 2004 Sep 2004 Oct 2004 Jun 2005 Jul 2005 Aug 2005 Sep 2005 May 2006 Jun 2006 Jul 2006 Aug 2006 Sep 2006 May 2004 Jun 2004 Jul 2004 Aug 2004 Sep 2004 Oct 2004 Jun 2005

Rainfall (mm)

Temperature (°C)

96.8 22.6 46.6 14.6 143 298.8 147.2 151.9 44.6 4.6 34 103.4 124.6 101.8 23 21.2 10.8 283.8 162.8 41.6 70.8 4.2 44.6 150.2 379.9 269.4 123.8

13.5 17.2 29.0 31.3 31.35 30.3 29.0 28.9 23.8 20.1 16.0 12.5 13.9 20.5 25.8 29.6 34.0 29.3 29.5 28.7 13.4 20.2 20.6 32.5 30.2 28.9 27.5

12.0 15.1 201.7 215.9 44.3 100.1 428.8 343.3 439.8 287.3 127.9 45.4

23.5 88.5 59.3 24.1 27.1 154.7 23.9 144.5 27.50 75.20 85.90 14.7

39.7 88.8 28.0 32.7 32.6

Humidity (%)

80.5 66.5 39.5 39.0 52.0 67.5 76.0 74.0 64.5 68.0 75.5 80.0 79.5 67.5 41.5 38.5 38.5 76.0 73.5 73.0 76.0 61.5 59.0 47.5 77.0 81.0 77.0 Roorkee; 29°52′04″N; 77°53′38″E;

pH

7.7 7.6 7.0 7.3 7.7 7.6 7.4 7.1 7.0 ‐ 6.6 ‐ 6.2 6.8 6.6 6.9 6.9 6.6 ‐ ‐ ‐ ‐ 7.0 7.6 6.3 6.4 6.8 274 m msl a ‐ 4.7 4.5 ‐ ‐ ‐ 6.7 6.9 6.7 7.6 6.3 6.2 7.8 ‐ ‐ ‐ ‐ ‐ ‐ ‐ Gomukh; 30°55′34″N; 79°04′15″E; 3800 m msl a 8.4 59.8 ‐ 9.6 73.0 ‐ 11.5 79.1 ‐ 10.4 86.2 ‐ 9.9 75.5 ‐ 4.1 82.5 ‐ 9.8 71.9 ‐ 10.4 92.6 ‐ 10.7 85.7 ‐ 8.9 78.3 ‐ 9.4 70.0 ‐ 9.6 75.6 ‐ 11.9 85.3 ‐ 10.7 87.7 ‐ 9.1 77.5 ‐ Gangotri; 30°59′48″N; 78°56′25″E; 3053 m msl a ‐ ‐ ‐ ‐ ‐ ‐ ‐

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EC (mS cm−1)

d 2H (‰)

d 18O (‰)

99 161 129 196 131 144 97 146 183 ‐ 310 ‐ 74 94 202 252 240 108 ‐ ‐ ‐ ‐ 200 214 90 106 43

‐ ‐ ‐ −10.7 +1.7 +0.4 −44.3 +10.3 −17.4 +2.3 −1.7 −37 ‐ −19.6 +20.5 ‐ ‐ −38.1 −12.7 −40.9 ‐ +6.5 −28.2 −12.5 −56 −73.8 −108.4

‐ −0.1 −1.8 −3.1 −1.2 −1.5 −6.8 +0.2 −3.5 −1.1 −0.6 −5.5 ‐ −3.4 +1.9 ‐ ‐ −54.2 −29.3 −62.4 ‐ +0.2 −4.1 −3.0 −8.1 −10.1 −13.9

‐ 33 28 ‐ ‐ ‐ 76 204 169 34 602 48 150 ‐ ‐ ‐ ‐ ‐ ‐ ‐

−56.2 ‐ −60.5 2.9 −9.4 −3.4 +5.4 +7.3 −22.5 −9.4 −45.8 −73.6 −24.2 −34.7 −19.4 −53.8 −93.4 −67.7 −73.9 −29.6

−8.4 −8.8 −8.8 −1.7 −3.8 −2.2 −0.6 +0.3 −3.9 −2.3 −6.3 −10.1 −4.6 −5.2 −3.4 −7.6 −12.6 −9.5 −10.3 −4.9

‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐

−6.2 −40.4 −26.0 −128.5 −165.7 −123.3 −31.6 −40.6 −124.7 −81.2 −228.3 −53.7 −91.1 −107.1 −128.4

−2.6 −6.7 −5.5 −17.5 −22.2 −16.5 −6.4 −7.6 −17.2 −11.8 −30.3 −8.4 −13.4 −15.3 −17.6

‐ ‐ ‐ ‐ ‐ ‐ ‐

‐ −37.6 −40.7 −109.8 −141.8 −119.6 +4.9

−6.2 −7.6 −6.7 −14.6 −19.9 −17.4 −1.8

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Table 1. (continued) Rainfall (mm) Jul 2005 Aug 2005 Sep 2005 May 2006 Jun 2006 Jul 2006 Aug 2006 Sep 2006

157.9 12.9 63.9 15.5 29.0 60.3 87.4 10.8

Aug 2004 Sep 2004 Oct 2004 Jul 2005 Aug 2005 Nov 2005 Dec 2005 Jan 2006 Feb 2006 Mar 2006 May 2006 Jun 2006 Aug 2006 Sep 2006

33.9 22.0 56.6 35.0 42.2 150.0 42.8

Dec 2005 Jan 2006 Feb 2006 Mar 2006 Apr 2006 May 2006 Jun 2006 Jul 2006 Aug 2006 Sep 2006 Oct 2006

10.0 89.6 18.2 89.2 55.2 144.7 77.4 430.4 323.5 119.2 41.6

Jun 2004 Jul 2004 Aug 2004 Sep 2004 Oct 2004 Dec 2004 Jan 2005 Feb 2005 Mar 2005 Apr 2005 May 2005 Jun 2005 Jul 2005 Aug 2005 Sep 2005 Oct 2005 Nov 2005 Dec 2005 Jan 2006 Feb 2006 Mar 2006 Apr 2006 May 2006 Jun 2006 Jul 2006 Aug 2006 Sep 2006 Oct 2006

496.2 636.0 100.4 117.0 6.8 102.6 126.6 59.2 30.6 97.2 79.0 692.1 277.1 220.2 2.6 ‐ 20.2 82.4 7.6 74.8 26.8 280.0 20.8 511.6 240.0 48.2 20.4

Jul 2004 Sep 2004 Oct 2004 Dec 2004 Jan 2005 Feb 2005 Mar 2005

101.9 101.0 67.3 8.0 58.4 86.0 31.8

117.0

Temperature (°C)

Humidity (%)

pH

‐ ‐ ‐ ‐ ‐ ‐ ‐ 6.3 Dabrani; 30°56′46″N; 78°41′17″E; 2050 m msl a ‐ ‐ ‐ ‐ ‐ 6.1 ‐ 5.9 ‐ ‐ 5.8 6.1 5.6 ‐ Maneri; 30°44′43″N; 78°26′48″E; 1150 m msl a ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ Uttarkashi; 30°43′45″N; 78°26′48″E; 1140 m msl a ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ 7.9 ‐ ‐ ‐ ‐ 6.3 6.3 ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ Tehri; 30° 21′10″N; 78°29′06″E; 640 m msl a 22.8 70.5 ‐ 21.3 77.5 ‐ 15.5 71.0 ‐ 10.4 68.0 6.1 7.1 73.5 ‐ 8.6 72.0 ‐ 14.6 60.5 ‐

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EC (mS cm−1)

d 2H (‰)

d 18O (‰)

‐ ‐ ‐ ‐ ‐ ‐ ‐ 8

−124.3 −68.9 −214.3 −13.2 −30.2 −72.4 −116.2 −96.6

−17.6 −9.3 −28 −3.1 −4.8 −9.9 −16.3 −12.4

‐ ‐ ‐ ‐ ‐ 84 ‐ 24 ‐ ‐ 168 15 4 ‐

−79.6 −39.1 −96.7 −91.7 −64.3 −53.2 −45.4 −35.3 −14.2 −90.0 +26.0 −71.6 −99.3 −34.6

−11.2 ‐ −13.6 −12.8 −9.3 −9.4 −8.9 −6.8 −3.9 −12.9 +2.5 −10.2 −13.3 −6.3

‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐

−23.5 −20.3 −13.4 −44.8 −19.3 +9.0 −18.4 −76.3 −85.5 −34.2 −14.1

−4.4 −4.4 −3.1 −7.4 −2.5 +2.0 −2.6 −11.0 −11.1 −5.8 −2.4

‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ 24 ‐ ‐ ‐ ‐ 149 90 ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐

‐ −6.5 −78.0 −2.8 −36.3 −13.0 −19.3 −18.1 −0.9 −17.3 +14.1 −0.3 −24.4 −46.9 −157.0 ‐ −90.0 −23.7 −16.9 +30.5 −19.1 +7.6 +14.6 −5.3 −62.2 −81.3 −20.5 −10.2

−2.5 −2.4 −11.1 −1.5 −6.4 −4.1 −4.8 −4.9 −2.5 −4.1 −1.4 −2.4 −5.2 −6.6 −20.8 −0.8 −12.5 −5.2 −4.8 +1.9 −4.2 +0 +0.1 −1.7 −9.7 −11.9 −4.0 −1.2

‐ ‐ ‐ 20 ‐ ‐ ‐

−26.8 −75.2 +5.0 +5.0 −7.2 −68.0 −26.3

−5.3 −10.4 +0.5 −1.3 −1.7 −9.8 −6.6

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Table 1. (continued)

May 2005 Jun 2005 Jul 2005 Aug 2005 Sep 2005 Feb 2006 Mar 2006 Apr 2006 May 2006 Jun 2006 Jul 2006 Aug 2006 Sep 2006 Oct 2006 Jun 2004 Jul 2004 Aug 2004 Sep 2004 Oct 2004 Feb 2005 Jun 2005 Jul 2005 Aug 2005 Sep 2005 Oct 2005 May 2006 Jun 2006 Jul 2006 Aug 2006 Sep 2006 Oct 2006 Aug 2006 Jul 2005 Aug 2005 Sep 2005 Oct 2005 Nov 2005 May 2006 Jun 2006 Jul 2006 Aug 2006 Sep 2006

Rainfall (mm)

Temperature (°C)

14.2 87.6 248.6 18.6 299.6 25.0 24.6 31.0 90.1 83.4 239.2 149.5 77.2 27.5

20.1 24.1 22.2 22.4 20.5 14.6 14.0 18.6 21.8 22.3 23.0 22.6 21.5 18.0

125.6 150.7 73.4 90.0 88.4 22.4 247.0 13.5 281.3 9.4 71.7 59.2 162.4 43.2

700.5 349.2 331.6 23.0 143.2 83.0 225.6 142.6 100.2

Humidity (%)

pH

41.0 ‐ 43.5 ‐ 81.5 ‐ 79.0 ‐ 80.0 ‐ 52.5 ‐ 55.5 ‐ 42.5 ‐ 59.0 ‐ 65.0 ‐ 79.5 ‐ 84.5 6.6 72.5 ‐ 67.0 ‐ Devprayag; 30°08′26″N; 78°35′48″E; 465 m msl a ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ 6.4 ‐ ‐ ‐ 6.1 ‐ ‐ ‐ Rishikesh; 30°06′44″N; 78°18′09″’E; 356 msl a ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐

EC (mS cm−1)

d 2H (‰)

d 18O (‰)

‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ 94 ‐ ‐

‐ −9.5 −78.0 −26.0 −169.0 ‐ ‐ ‐ −27.0 −60.8 −61.6 −79.4 −102.6 −3.3

‐ −2.3 −10.6 −4.9 −22.0 ‐ ‐ ‐ −2.4 −8.2 −9.4 −11.4 −14.0 −2.5

‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ 54 ‐ ‐ ‐ 20 ‐ ‐ ‐

−14.5 −29.1 −79.8 −26.3 −44.1 −51.6 ‐ −71.7 −59.7 −160.0 −30.0 −4.8 −61.1 ‐ −66.4 −84.7 −23.0 −59.4

−3.1 −5 −10.7 −4.4 −6.8 −7.4 ‐ −10.2 −8.6 −20.7 −5.1 −0.9 −7.7 −10.0 −10.9 −11.4 −5.1 −8.2

‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐ ‐

−90.7 −43.8 −112.2 −65.1 −72.4 ‐ −47.0 ‐ −62.9 −58.7

−11.8 −6.5 −14.4 −8.8 −10.3 ‐ −6.6 ‐ −8.6 −8.2

a

Site name, latitude (N), longitude (E), and altitude (m mean sea level (msl)).

Figure 2. Variation of weighted d 2H versus d18O in precipitation representing Indian meteoric waterline (IMWL). 8 of 15

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tion is from the Arabian Sea whereas during the winter the retreat of monsoon and air moisture masses with “depleted” isotopic composition, which originate because of westerly disturbances in the Mediterranean Sea, are the sources of precipitation. [12] The plots of d 2H versus d18O for precipitation in different regions like northern India, southern India, and western Himalayas are shown in Figures 3a–3c, and their respective regional meteoric waterlines (RMWL) are given as equations (12)–(14):  2 H ¼ 8:15ð0:12Þ  18 O þ 9:55ð0:80Þ ðn ¼ 65; r2 ¼ 0:99 ; ð12Þ  2 H ¼ 7:82ð0:17Þ  18 O þ 10:23ð0:85Þ ðn ¼ 62; r2 ¼ 0:97 ; ð13Þ  2 H ¼ 7:95ð0:09Þ  18 O þ 11:51ð0:89Þ ðn ¼ 123; r2 ¼ 0:99 : ð14Þ

Figure 3. Regional meteoric waterline for (a) northern India, (b) southern India, and (c) western Himalayas. plot is shown in Figure 2. This plot represents the Indian meteoric waterline (IMWL) for a complete year which is not very different from the GMWL (equation (1)).  2 H ¼ 7:93ð0:06Þ  18 O þ 9:94ð0:51Þ ðn ¼ 272; r2 ¼ 0:98 : ð8Þ

The IMWL for summer (equation (9)), monsoon (also called as SW monsoon; equation (10)) and winter (also called as NE monsoon; equation (11)) are also established which have almost similar slopes except for the summer equation because of the evaporation effect.  2 H ¼ 7:38ð0:21Þ18 O þ 8:03ð1:05Þ ðn ¼ 81; r2 ¼ 0:94 ; ð9Þ  2 H ¼ 7:98ð0:078Þ18 O þ 9:29ð0:679Þ ðn ¼ 134; r2 ¼ 0:99 ; ð10Þ  2 H ¼ 7:81ð0:17Þ18 O þ 11:14ð1:18Þ ðn ¼ 63; r2 ¼ 0:97 ; ð11Þ

The IMWL for the winter season (equation (11)) has an intercept a little higher than that of the summer and monsoon seasons, indicating differences in their sources of precipitation. During the monsoon, the main source of precipita-

The RMWLs for the northern India and the western Himalayas show only minor differences in intercept. The slightly higher intercept in case of the western Himalayan region compared to that of the other regions possibly indicates contribution of local air masses through evapotranspiration occurring at lower temperature. In addition, the effect of western disturbances from the Mediterranean Sea also dominates in the western Himalayan during the winters causing different slope and intercept. [13] The local meteoric waterlines (LMWL) for various locations in the western Himalayas like Dabrani (equation (15)), Devprayag (equation (16)), Gangotri (equation (17)), Gomukh (equation (18)), Jammu (equation (19)), Maneri (equation (20)), Rishikesh (equation (21)), Tehri (equation (22)) and Uttarkashi (equation (23)) (Figure 1 and Table 2) are established using the isotopic data from the period 2003–2005. Also given for comparison is the LMWL for Nainital [Nachiappan et al., 2002, equation (24)]. [14] The LMWLs in most cases do not show much difference in slope and intercept whether the isotopic data are taken for all seasons in a year or only for the monsoon season. This is because more than 70% of rainfall occurs in India during the monsoon season. The elevation difference between Rishikesh (347 m above sea level (asl)) and Gomukh (3800 m asl) produces an altitude effect in rainfall of −0.25‰ to −0.29‰ in d18O 100 m−1 [Kumar et al., 2006]. The higher slopes and intercepts in case of LMWLs for Gomukh, Gangotri, and few other sites indicate sources of moisture other than the moisture laden air from a sea/ocean. The same reason as mentioned in the case of RMWL for western Himalayas is applicable here. The LMWL for Maneri and Nainital show an unexpected decrease in intercept and slope that indicates the considerable contribution of local moisture masses due to evaporation. This can be justified as Nainital Lake is surrounded by hills, while Maneri Dam is located near Maneri. However, since the precipitation at Uttarkashi does not show the effect of evaporation, it appears that the water vapors from the Maneri Dam move toward the Dabrani site and are able to precipitate with moisture laden air from the normal clouds in the area near Dabrani.

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Station Name

Dabrani Devprayag Gangotri Gomukh Jammu Maneri Rishikesh Tehri Uttarkashi Nainital

Roorkee Lucknow Patna Sagar Allahabad

Delhi

Bangalore Belgaum Tirunelveli Lower Maner

Kakinada Kolkatta Taramani Kozhikode

Mumbai

Station Number

1 2 3 4 5 6 7 8 9 10

11 12 13 14 15

16

17 18 19 20

21 22 23 24

25

Local Meteoric Waterline (LMWL) Based on Monsoon Data

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d 2H = 7.20(±0.10) × d 18O + 2.70(± 0.80) (r2 = 0.97)

d 2H = 8.00(±0.3) × d 18O + 8.40(±0.80) (r2 = 0.94)

d 2H = 7.4(±0.5) × d 18O + 7.6(±0.90) (n = 46, r2 = 0.86)

Coastal Locations d 2H = 8.23(±0.38) × d 18O + 9.63(±1.69) (n = 12, r2 = 0.98) d 2H = 7.86(±0.29) × d 18O + 10.28(±1.61) (n = 23, r2 = 0.97) 2 18 2 d 2H = 9.13(±1.52) × d 18O + 16.19(±10.91) (n = 8, r2 = 0.86) d H = 8.03(±0.71) × d O + 8.27(v5.62) (n = 12, r = 0.93) ‐ d 2H = 8.13(±0.18) × d 18O + 13.08(±1.42) (n = 5, r2 = 0.99) d 2H = 7.20(±0.3) × d 18O + 7.90(±1.10) (n = 11, r2 = 0.98) d 2H = 7.20(±0.2) × d 18O + 7.60(±0.80) (r2 = 0.99)

Southern India d 2H = 6.59(±1.09) × d 18O + 7.41(±3.85) (n = 5, r2 = 0.92) d 2H = 7.82(±0.34) × d 18O + 11.74(±1.78) (n = 11, r2 = 0.98) d 2H = 7.45(±1.57) × d 18O + 11.16(±3.57) (n = 6, r2 = 0.85) d 2H = 7.78(±0.62) × d 18O + 11.32(±2.28) (n = 12, r2 = 0.94) d 2H = 7.32(±0.87) × d 18O + 5.58(±2.78) (n = 6, r2 = 0.95) d 2H = 7.09(±0.54) × d 18O + 5.39(±1.78) (n = 12, r2 = 0.95) ‐ d 2H = 7.80 × d 18O + 6.50 (r2 = 0.97)

d 2H = 7.20(±0.10) × d 18O + 4.60(±0.50) (r2 = 0.95)

Northern India d 2H = 7.90(±0.31) × d 18O + 7.27(±2.20) (n = 8, r2 = 0.99) d 2H = 8.23(±0.43) × d 18O + 11.72(±2.33) (n = 12, r2 = 0.99) 2 18 2 d 2H = 6.75(±0.36) × d 18O − 3.31(±3.07) (n = 6, r2 = 0.99) d H = 7.81(±0.60) × d O + 6.50(±4.95) (n = 7, r = 99) d 2H = 9.16(±0.17) × d 18O + 12.46(±1.54) (n = 3, r2 = 0.99) d 2H = 7.76(±0.66) × d 18O + 3.02(±7.43) (n = 5, r2 = 0.98) d 2H = 7.80(±0.21) × d 18O + 7.97(±1.35) (n = 8, r2 = 0.99) d 2H = 7.91(±0.29) × d 18O + 8.23(±1.81) (n = 14, r2 = 0.98) d 2H = (7.50 ± 0.50) × d 18O + 4.40(± 4.80) (r2 = 0.99) d 2H = 7.50(±0.20) × d 18O + 4.40(±1.90) (r2 = 0.99)

Western Himalayas d 2H = 9.00(±0.35) × d 18O + 21.25(±3.82) (n = 5, r2 = 0.99) d 2H = 8.04(±0.40) × d 18O + 14.20(±3.93) (n = 13, r2 = 0.97) d 2H = 8.27(±0.38) × d 18O + 12.43(±4.33) (n = 8, r2 = 0.99) d 2H = 8.07(±0.30) × d 18O + 9.54(±2.69) (n = 16, r2 = 0.98) d 2H = 7.73(±0.28) × d 18O + 6.21(±4.57) (n = 9, r2 = 0.99) d 2H = 8.01(±0.24) × d 18O + 12.69(±3.37) (n = 14, r2 = 0.99) d 2H = 8.49(±0.12) × d 18O + 21.49(±1.80) (n = 9, r2 = 0.99) d 2H = 8.22(±0.10) × d 18O + 17.12(±1.53) (n = 15, r2 = 0.99) d2H = 8.48(±0.20) × d 18O + 12.10(±1.40) (n = 12, r2 = 0.99) d 2H = 8.11(±0.19) × d 18O + 9.29(±1.00) (n = 24, r2 = 0.99) d2H = 7.88(±0.75) × d 18O + 7.10(±6.33) (n = 4, r2 = 0.98) d 2H = 7.31(±0.52) × d 18O + 4.84(±3.00) (n = 12, r2 = 0.95) d 2H = 8.70(±0.10) × d 18O + 12.31(±1.02) (n = 5, r2 = 0.99) d 2H = 8.47(±0.31) × d 18O + 10.43(±3.03) (n = 8, r2 = 0.99) d 2H = 8.47(±0.18) × d 18O + 15.73(±2.21) (n = 8, r2 = 0.99) d 2H = 7.94(±0.33) × d 18O + 9.37(±3.01) (n = 17, r2 = 0.97) d 2H = 8.23(±0.22) × d 18O + 14.37(±2.18) (n = 9, r2 = 0.99) d 2H = 8.07(±0.23) × d 18O + 13.89(±1.68) (n = 23, r2 = 0.98) ‐ d 2H = 7.50 × d 18O + 4.82 (n = 15, r2 = 0.97)

Based on All Seasons

Table 2. Local Meteoric Waterlines (LMWL) Developed From the Present Study for the Various Stations

Equation Equation Equation Equation [Deshpande et Equation [Deshpande et

(35) (36) (37) (38) al., 2003] (39) al., 2003]

Equation (31) Equation (32) Equation (33) Equation (34) [Kumar et al., 1982]

Equation (25) Equation (26) Equation (27) Equation (28) Equation (29) [Gupta and Deshpande, 2005] Equation (30) [Gupta and Deshpande, 2005]

Equation (15) Equation (16) Equation (17) Equation (18) Equation (19) Equation (20) Equation (21) Equation (22) Equation (23) Equation (24) [Nachiappan et al., 2002]

Remarks

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Figure 4. Plot of slope versus D excess. [15] The LMWLs established for inland locations of northern India (Roorkee (equation (25)), Lucknow (equation (26)), Patna (equation (27)), and Sagar (equation (28))) also show variations in the slope and intercept (Table 2). Also, the LMWLs for Allahabad [Gupta and Deshpande, 2005, equation (29)] and Delhi [Mukherjee and Chandrasekharan, 1993, equation (30)] are given for the purpose of comparison. It has been observed that the slope and intercept decrease where surface water bodies occur and where the temperature is higher, e.g., Sagar Lake at Sagar and the river Ganga at Allahabad, because of very wide course with impounded water. Similarly, Delhi has a number of impounded water bodies that contribute considerable local moisture masses and the precipitation in low amount is also subjected to evaporation during the rainout, causing a decrease in slope and intercept. [16] The LMWLs for a few locations in southern India are given in Table 2 (Bangalore (equation (31)), Belgaum (equation (32)) and Tirunelveli (equation (33))). Also, the LMWL for lower Maner [Kumar et al., 1982, equation (34)] is given for the purpose of comparison. The slope is less in each case than the IMWL because of evaporative enrichment of raindrops during the rainout processes. However, as Tirunelveli is warmer (ambient temperature is 37°C, relative humidity is 60%) than Bangalore and Bangalore is warmer than Belgaum therefore the effect of evaporation increases the slope and intercept from Tirunelveli to Belgaum. [17] The LMWLs for different coastal locations like Kakinada (equation (35)), Kolkata (equation (36)), and Taramani (equation (37)) vary in terms of slope as well as in intercept (Table 2). Also, the LMWLs for Kozhikode and Mumbai [Deshpande et al., 2003] are given for the purpose of comparison. The one reason of variation of slope is that the NE monsoon that originates from BOB has comparatively depleted (more negative) isotopic composition (−1.5‰ to +5‰), while the SW monsoon that originates from the Arabian Sea has an isotopic composition +5‰ to +1.5‰. In addition, the SW monsoon from the west coast moves toward the east coast and gets depleted because of rainout processes, i.e., progressive depletion of vapor phase and preferential condensation of heavier isotopes and also mixes with the evaporated air moisture masses. [18] Furthermore, the variation in isotopic composition of precipitation in different parts of India like south, north, etc. can be explained with the fact that the rainwater characteristics in the southern Indian Peninsula are controlled by precipitation during the summer (SW) and winter (NE) monsoons. The SW monsoon operates during the months of June–September, and the NE monsoon operates during the

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months of October–January. The causal mechanism for these monsoon systems is the seasonal reversal of temperature and pressure gradients and associated wind circulation following the annual northward and southward motion of the Sun [Rajan, 1988; Rao, 1976]. These two seasonal circulation systems are part of the larger monsoon circulation of South Asia. [19] The major sources of moisture for the SW monsoon rains in the southern Indian Peninsula are the northern Indian Ocean and the Arabian Sea, leading to rains along the west coast of India and in the central and eastern parts of the peninsula [Ghosh et al., 1978]. Whereas the NE monsoon derives moisture from the Bay of Bengal, the South China Sea, and the continental vapor sources to provide precipitation to eastern and southeastern parts of the peninsula [Rao, 1976; Mooley and Shukla, 1987; Rajan, 1988; Menon, 1995]. The two sources of moisture in the two seasons are expected to have different isotopic characteristics whose imprints are identifiable in the geographic distribution of isotopes in precipitation. [20] In addition to the SW and NE monsoons in northern India, the westerly disturbances from the Mediterranean Sea are responsible for the variability in the isotopic characteristics of precipitation. It has been observed in most of the cases that the isotopic composition of precipitation is more depleted in the month of September in comparison to July and August every year. [21] The plot of deviation in D excess versus slope of local meteoric waterlines is shown in Figure 4. This plot clearly indicates that there is a relationship between slopes and D excess that varies linearly. However, the linear variation is different (Figure 5) for coastal region (S = 0.21 × D excess + 5.86 (r2 = 0.82)), central region (S = 0.19 × D excess + 6.40 (r2 = 0.71)), and western Himalayas (S = 0.06 × D excess + 7.32 (r2 = 0.82). [22] The decrease in slope of the best fit line drawn between slope of local meteoric waterlines and D excess from coastal to mountainous region is because the partitioning of heavier isotopes in precipitation occurs at a faster rate in coastal areas, and as the clouds progress, the rate of this process decreases because of less availability of the heavier isotopes subsequently in the clouds. [23] For most of the stations, the plot of d 18O versus humidity (Figure 6a) and air temperature (Figure 6b) gave a poor correlation indicating complex isotopic fractionation during rainout process like possible several sources of condensing moisture, secondary effects, etc. Hence, it calls for further detailed long‐term research on the same. A similar

Figure 5. Variation of slope and D excess in different parts of India.

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Figure 6. (a and b) Plot of d 18O versus humidity and air temperature for Bangalore.

Figure 7. (a–d) Plot of d 18O versus rainfall for Jammu, Sagar, Tirunelveli, and Kolkata. 12 of 15

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elevation (r2 > 0.7) for August (Figures 9a–9c) and −0.3 to −0.5‰ 100 m−1 elevation (r2 > 0.6) for September (Figures 10a–10c). Whereas the “altitude effect” in the d 18O content of precipitation for the same region considering the rainfall throughout the year was estimated (−0.1 to −0.3‰ 100 m−1 elevation (r2 > 0.4)) (Figures 11a–11c). This probably indicates that the use of “altitude effect” in the isotopic composition of precipitation for hydrological investigations like identification of recharge areas of springs in the mountainous region needs to be done with utmost care and the values to be used appropriately on the basis of the geomorphologyical and hydrogeological settings of the area that is being studied.

5. Conclusions [26] The Indian meteoric waterline, regional meteoric waterline for the northern, southern India, and western Himalayas, including local meteoric waterlines for different locations have been established, and meteoric waterlines show significant differences in slope and intercept of d 2H‐d18O plots, particularly in case of RMWL and LMWL because of mixing of local air moisture masses in the precipitation coupled with change in weather and topographical conditions. The d2H and d18O values of precipitation in plains regions show a wide range of variations (d 2H = −75.6‰ to −1.1‰ and d 18O = −11‰ to −0.44‰) mostly

Figure 8. The estimate on the “altitude effect” in d18O of precipitation for the SW monsoon period in the years (a) 2004, (b) 2005, and (c) 2006. finding was made by Yurtsever and Gat [1981] during a study to develop a relationship between the isotopic composition of precipitation as a function of different independent variables, namely, latitude, temperature, and amount of precipitation. The authors pointed out that this approach may be true on a global scale and may not hold good on a regional scale and suggested that certain geographical/climatologically parameters may be included for better results. [24] The plot of d 18O versus amount of rainfall (Figures 7a and 7b) for various stations indicated good correlation only for western Himalayas and northern Indian stations with higher amount of rainfall giving rise to depleted d18O values, indicating the “amount effect” in precipitation. Whereas “the amount effect” is not clearly seen in southern Indian (Figure 7c) and coastal regions (Figure 7d). The “amount effect” is seen only during the SW monsoon period in southern and coastal regions. [25] The “altitude effect” in the d18O content of precipitation for the western Himalayan region was estimated separately for the SW monsoon period (Figures 8a–8c) and found to be ranging from −0.1‰ to −0.4‰ 100 m−1 elevation (r2 > 0.5). The monthly estimate of the same during the monsoon period gave a value of −0.2 to −0.3‰ 100 m−1

Figure 9. The estimate on the “altitude effect” in d18O of precipitation in August during (a) 2004, (b) 2005, and (c) 2006.

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due to the continental and seasonal effects coupled with amount effect, as the variation in altitude is only a few 100 m. The precipitation in western Himalayas also has wide variations (d2H = −228.3‰ to +30.5‰ and d18O = −30.0‰ to +2.5‰). The higher depletion is due to higher altitude (altitude effect) and continental effect, while the enrichment may be caused by higher evaporation of raindrops during the lesser amount of rainfall (amount effect) that predominates at higher altitudes because of higher intensity of infrared radiations. This along with possible contributions from the western disturbances from the Mediterranean Sea could be the reason for “highly enriched” isotopic values at Gomukh. Thus, the precipitation particularly at Gomukh (elevation is 3800 m asl) covers the maximum range of variation in the isotopic composition (d 18O = −22.2‰ to +1.2‰). The precipitation is more depleted in isotopic values in September than the other months of the monsoon season. It is due to the amount effect and indicates the shifting of monsoon toward later months of the monsoon season. The effect of evaporation and transpiration is identifiable in precipitation, and these parameters can be quantified. [27] A clear “amount effect” in the isotopic composition of precipitation was seen for all seasons in the northern Indian and western Himalayan stations. Whereas “amount effect” was seen only during the SW monsoon period for the

Figure 11. The estimate on the “altitude effect” in d18O of precipitation considering the rainfall throughout the year during (a) 2004, (b) 2005, and (c) 2006. rest of stations. The “altitude effect” in the isotopic composition of precipitation is not a constant value, and it varies from month to month. [28] Acknowledgments. The authors are thankful to Pradeep Aggarwal, Head, Isotope Hydrology Section, IAEA, Vienna, Austria for getting some of our precipitation samples analyzed at the IAEA, Isotope Hydrology Laboratory at Vienna. The authors express their sincere gratitude to Noble Jacob of the Isotope Hydrology Section, Bhabha Atomic Research Centre, Mumbai for help during sampling in the Bhagirathy catchment and to the Director, National Institute of Hydrology, Roorkee, for supporting the study of isotopic signatures of precipitation and groundwaters in various parts of India.

References

Figure 10. The estimate on the “altitude effect” in d18O of precipitation in September during (a) 2004, (b) 2005, and (c) 2006.

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