Climate change and the precipitation variations in the northwestern Himalaya:

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1 INTERNATIONAL JOURNAL OF CLIMATOLOGY Int. J. Climatol. 30: (2010) Published online 9 April 2009 in Wiley InterScience ( DOI: /joc.1920 Climate change and the precipitation variations in the northwestern Himalaya: M. R. Bhutiyani, a *V.S.Kale b and N. J. Pawar c a Department of Geology, College of Military Engineering, Pune, India b Department of Geography, University of Pune, India c Department of Geology, University of Pune, Pune, India ABSTRACT: Using available instrumental records, this paper examines the variation of precipitation from 1866 to 2006 in the northwestern Himalaya (NWH). The study indicates no trend in the winter precipitation but significant decreasing trend in the monsoon precipitation during the study period. Periodicities on a multi-decadal scale (29 34 years and years) obtained in power spectrum analyses point towards epochal behaviour in the precipitation series. Analyses of the temperature data show significant increasing trends in annual temperature in all three stations in the NWH during the data period. Warming effect is particularly noteworthy during the winter season. Negative relationships between mean winter air temperature and snowfall amounts recorded at different meteorological stations in this period reveal strong effect of rising temperatures on the decreasing snowfall component in total winter precipitation, reducing effective duration of winter on the windward side of the Pir Panjal Himalayan Range. The study also shows influence of global teleconnections [North-Atlantic Oscillation (NAO) during winter months and Southern Oscillation Index (SOI) during the monsoon months] on precipitation fluctuations in the NWH. The teleconnections that appear to exist between the precipitation and the temperature until the late 1960s seem to have weakened considerably in the last three decades. This may be ascribed to the diminishing effect of the natural factors such as quasi-biennial oscillations (QBO), El Niño Southern Oscillations (ENSO), double sunspot cycles (Hale), etc., in this period. Role of increasing concentration of greenhouse gases in the atmosphere cannot be ruled out. Copyright 2009 Royal Meteorological Society KEY WORDS northwestern Himalaya; climate change; winter and monsoon precipitation; epochal behaviour; global teleconnections; greenhouse gases Received 22 September 2007; Revised 10 March 2009; Accepted 13 March Introduction The global warming is an undeniable fact of our lives today and its impacts are being felt all over the world by way of rising air temperature, changes in precipitation and faster melting of the glaciers. These have led to increased discharge in the rivers and consequent sealevel rise. Significant increase in the global air temperature by about 0.5 to 1.1 C in the last 150 years (Jones et al., 1986a, 1986b; Vinnikov et al., 1990; Karl et al., 1995; Fallot et al., 1997; Zhai et al., 1999; Crowley, 2000; IPCC, 2001; Knappenberger et al., 2001; IPCC, 2007), coinciding with the industrial revolution, has been attributed to the excessive release of greenhouse gases such as CO 2, CO, methane, nitrous oxide, etc. The rise in temperature was not at a uniform rate during this period and decadal variations with episodes of strong warming and cooling were experienced. Warming appears to have enhanced from late 1960s and highest rates of increase were recorded in the last two decades (Oerlemans, 1994; Easterling et al., 1997; De and Mukhopadhyay, 1998; * Correspondence to: M. R. Bhutiyani, Department of Geology, College of Military Engineering, Pune , India. mahendra bhutiyani@yahoo.co.in Qiang et al., 2004; Schaer et al., 2004). Conforming to the global trends, the mountainous areas such as the Alps, the Rockies and the Andes have also warmed significantly (Beniston et al., 1997; Diaz and Bradley, 1997; Wibig and Glowicki, 2002; Beniston, 2003; Diaz et al., 2003; Villaba et al., 2003; Vuille et al., 2003; Rebetez, 2004). Although pre-monsoon (March to May) and summer cooling have been reported in some portions of the western Himalaya (Yadav et al., 2004) and Upper Indus basin (Fowler and Archer, 2006), overall annual temperatures in the Himalayas have recorded significant increase in the last century (Pant and Borgaonkar, 1984; Seko and Takahashi, 1991; Sharma et al., 2000; Bhutiyani et al., 2007). Rising global temperature may have triggered largescale changes in the energy exchange processes (radiative forcings), affecting the atmospheric circulation and the global precipitation patterns (Fallot et al., 1997; Zhai et al., 1999; Beniston, 2003). Mixed results have been obtained in various studies in different parts of the world. Overall increase of 5 10% in annual precipitation over most mid and high latitudes of the northern hemisphere and decrease by an average 3% in subtropical areas have been reported (Vinnikov et al., 1990; IPCC, 2001). The Copyright 2009 Royal Meteorological Society

2 536 M. R. BHUTIYANI ET AL. studies in China (Zhai et al., 1999), former Soviet Union (FSU) (Fallot et al., 1997), South America (Vuille et al., 2003), North America (Ellsaesser et al., 1986), Europe (Beniston, 1997), Peninsular India (Pant et al., 1988; Thapliyal and Kulshrestha, 1991; Srivastava et al., 1992; Pant and Rupa Kumar, 1997), Nepal Himalaya (Shreshtha et al., 2000) and Upper Indus basin (UIB) in the northwestern Himalaya (NWH) (Archer and Fowler, 2004) have shown minor and statistically insignificant variations in the precipitation in the last century. The underlying reason behind this could be that unlike temperature, the fluctuations in precipitation, being region-specific, may not have followed a uniform global trend or pattern and local factors such as orography, geographical location of the area, etc., may have played a vital role. The ecosystems which are most vulnerable to the spectre of the climate change are the high mountain areas such as the Alps, the Rockies, the Andes and the Himalayas, etc. (Beniston, 2003). The impacts of increasing global air temperature on the vast expanse of water existing in the form of glacier-ice and snow, the forest cover, the health and the socio-economic conditions of the population inhabiting these regions could be extremely disturbing. While these effects have been studied and globally welldocumented by many scientists, the Himalayan region remains poorly studied, largely because of inadequate meteorological and hydrological database (Liu and Chen, 2000; Ma et al., 2006). Hydrology of many Himalayan rivers is controlled by monsoon and winter precipitation and climate-induced changes may prove to be detrimental to the economic and social well-being of a large population. The present study assumes significance because of the important role played by the Himalayas in the Indian subcontinent, which act as the greatest mountain barrier on the Earth, where polar, tropical and Mediterranean influences interact and affect the monsoon systems over the Asian continent (Borgaonkar and Pant, 2001) and attempts to understand the climate change in this datasparse region over a longer time-span of about 140 years ( ). 2. The study area The NWH, covering the states of Jammu and Kashmir and Himachal Pradesh with the river basins of the Jhelum, Satluj, Chenab, Ravi and Beas, are bound by longitudes 72 E to 80 E and latitudes 30 N to 37 N (Figure 1). Altitudes in the region vary from a few hundred meters in the Siwalik Himalaya in the south to about 8000 m in the Karakoram Himalaya in the north. Precipitation in the NWH occurs under the influence of westerly disturbances during the months from October to May and due to the southwest monsoon from July to September. Different parts of the region experience varied climatic conditions. The extreme eastern part with little vegetative cover near Tibet experiences a cold dry climate with limited precipitation, both in the form of rain and snow. The western part is endowed with comparatively Figure 1. Map of the northwestern Himalaya (NWH) showing approximate locations of various ranges ( and the meteorological stations (ž). SML, Shimla; LH, Leh; GMG, Gulmerg; HDT, Haddan Taj; SLG, Solang; KZN, Kanzalwan; PTS, Patseo; BHG, Bahang; DHD, Dhundi; SGR, Srinagar. moist weather with moderate precipitation (snow and rain), evergreen to semi-evergreen forest cover with many rivers and valleys. Depending upon the altitude, different ranges in the NWH receive different amounts of snowfall ranging from about 100 to >1600 cm. Annual winter snowfall is at a maximum in the Pir Panjal Range and it decreases as one goes northwards towards the Great Himalaya, Zanskar, Ladakh and Karakoram ranges. In higher altitudes, temperatures remain subzero for the major part of the year and the winter precipitation is mostly in the form of snow (Bhutiyani, 1992). Precipitation due to the monsoon is highest in Siwalik and the Pir Panjal Ranges and it reduces northwards into the Great Himalaya, Zanskar, Ladakh and Karakoram ranges (Rakhecha et al., 1983). 3. Data and methodology The precipitation and temperature data of two seasons namely, winter (from November of the last year to April of the current year) (SASE, 1999) and monsoon (June to September) and total annual precipitation, were used to study the trends and temporal fluctuations in climate over the NWH. Table I gives the details of the data stations, data types/variables, their time-spans and sources. Locations of these stations are shown in Figure 1 and their physiographic details are given in Table II. It is seen from Table I that long-term precipitation data for 140 years ( ) and temperature data

3 CLIMATE CHANGE AND THE PRECIPITATION VARIATIONS IN THE NORTHWESTERN HIMALAYA 537 Station Table I. Details of the data stations used in this study. Data type/variables Time span Data source 1. Srinagar (J&K) A, B, C IMD 2. Leh (J&K) A, B, C Shimla (H.P.) A IMD B IMD C IMD 4. Haddan Taj C, D SASE # (J&K) 5. Gulmerg (J&K) C, D SASE # 6. Kanzalwan C, D SASE # (J&K) 7. Bahang (H.P.) C, D SASE # 8. Solang (H.P.) C, D SASE # 9. Dhundi (H.P.) C, D SASE # 10. Patseo (H.P.) C, D SASE # See Figure1 for locations of stations. A, monthly precipitation in mm; B, monthly maximum and minimum air temperature in C; C, monthly air temperature in C; D, monthly winter snow depth in cm; J&K, Jammu and Kashmir; H.P., Himachal Pradesh. India Meteorological Department, Indian Air Force Station, Leh. # Snow and Avalanche Study Establishment, Manali (India). for 130 years ( ) are available from only one station namely, Shimla. Srinagar and Leh data are of relatively shorter duration ( ). Winter precipitation (snowfall amounts in cm) and temperature data for seven stations spread over Jammu and Kashmir and Himachal Pradesh are available in published form for varying periods in last three decades. The stations are maintained by India Meteorological Department (IMD) and Snow and Avalanche Study Establishment (SASE). Instruments standardized by the IMD such as dry bulb and wet bulb, maximum and minimum thermometers, rain guages and snow stakes are used to record quality data at all stations. Eurasian snow cover area (March) data ( ) were obtained from Brown (2002) and monthly North-Atlantic Oscillation Index (NAO) ( ) and Southern Oscillation Index (SOI) data ( ) from the websites htpp://cru@uea.ac.uk and respectively. The quality of the precipitation and temperature data had to be ascertained because of the limited database. Leh had a few missing data points in its precipitation series. These were filled by using a temporal interpolation method (Mitchell et al., 1966). Spatial and temporal compatibility of the data recorded at the three meteorological stations were verified by double-mass curves, simple linear correlation and regression analyses (Mutreja, 1986). Good temporal and spatial compatibility as revealed by the straight-line graphs of double-mass curves (not shown here) indicate that the data recorded at these three stations can be collectively used to investigate long-term trends in precipitation and temperature in the NWH. In order to bring uniformity and facilitate comparison between different stations, their data were standardized by subtracting the mean and dividing by their standard deviation (Pant and Rupa Kumar, 1997; Shreshtha et al., 2000). Similarly, mean annual winter and monsoon diurnal temperature range (DTR) data for Srinagar, Leh and Shimla were computed by subtracting the mean minimum temperature from mean maximum temperature for each station during a particular season. The DTR values were also standardized as per the method discussed earlier. The SPI (Standardized Precipitation Index) and STI (standardized temperature index) series for the whole Table II. Physiographic details of the meteorological stations used in this study. Station Altitude (m) Latitude/Longitude Land cover and surroundings of the station 1. Srinagar N/74 47 E A lacustrian flatland in an urban area on the banks of Jhelum River on the leeward side of the Pir Panjal Range. 2. Leh N/77 58 E A flat river terrace in a widened valley of Indus River on the windward side of the Ladakh Range. 3. Shimla N/77 10 E A forested high ground in an urban area on the windward side of the Pir Panjal Range. 4. Haddan Taj N/74 02 E A grassy high ground on the leeward side of Pir Panjal Range. 5. Gulmerg N/74 23 E A grassy flatland in a widened forested valley, on the leeward side of the Pir Panjal Range. 6. Kanzalwan N/74 42 E A forested high ground on the northern slope of a hill feature on the windward side of the Great Himalayan range. 7. Bahang N/77 13 E A forested raised high ground on a river-bed, alongside the river on the windward side of the Pir Panjal Range. 8. Solang N/77 09 E A flat forested terrace in a valley, alongside the river on the windward side of the Pir Panjal Range. 9. Dhundi N/77 07 E A grassy high ground in a valley, surrounded by an open forest, on the windward side of the Pir Panjal Range. 10. Patseo N/77 15 E A flat area in the valley region, surrounded by barren mountains, on the windward side of the Great Himalayan range.

4 538 M. R. BHUTIYANI ET AL. region of the NWH for the period from 1901 to 1989 were calculated arithmetically by averaging the SPI and STI records of all the three stations namely, Shimla, Srinagar and Leh (Pant and Rupa Kumar, 1997; Shreshtha et al., 2000). Because of the availability of reasonably long precipitation and temperature records and its positive bivariate correlation (r = 0.51, significant at 95% confidence level) with the NWH data for annual, monsoon and winter series, Shimla was chosen as a reference station to extend the NWH SPI and STI series up to 2006 by the following method (Singh and Sontakke, 2002): 1. Using the linear relationship between Shimla and NWH series, the SPI and STI values for NWH were estimated from 1901 to Standard deviations of both, original and estimated series of the NWH were computed. The factor p (ratio of standard deviation of the original series to that of the estimated series) for each series was calculated. 2. To calculate a 1-year forward extension of NWH SPI and STI series, i.e. 1990, the values of SPI and STI were estimated from the linear regression equations between the NWH and Shimla series. These estimated values were inflated by their respective p factors and the final values for the year 1990 for NWH were obtained. A similar procedure was adopted for subsequent years up to The long-term trends in the SPI and STI time series were evaluated by using standard parametric and nonparametric statistical techniques, such as linear regression analysis (Pant and Rupa Kumar, 1997; Borgaonkar and Pant, 2001) and the Mann Kendall test (Kendall and Stuart, 1961; Mitchell et al., 1966). To evaluate periodicity, the data were subjected to power spectrum analyses (Blackman and Turkey, 1958). The data smoothing was done using the cubic spline method with 50% variance reduction frequency (Pant et al., 1988) to remove interannual variability. 4. Results For better understanding of potential impacts of the climate change in this poorly studied region of the NWH, trend analyses of the precipitation and temperature data were carried out. Summary of results using both techniques of trend determination and linear regression plots of annual, monsoon and winter SPI and STI series of three stations, namely Srinagar ( ), Leh ( ), Shimla ( ) and NWH ( ) are given in Tables III and IV and Figures 2 and 3, respectively. The b coefficients values, which indicate the rate of change in precipitation and temperature with time, are also given along with the regression equations in the figures. The trend analyses show increasing but statistically insignificant trend (at 95% confidence level) in winter precipitation during the study period in the NWH Table III. Results of trend analysis of annual, winter and monsoon precipitation in the NWH. Station Data span Trend analysis Mann Kendall s non-parametric test Linear regression coefficient b (a) Total annual precipitation 1. Shimla ( ) ( ) 2. Srinagar (+) (+) 3. Leh ( ) ( ) 4. NWH ( ) ( ) (b) Total winter precipitation 1. Shimla ( ) ( ) 2. Srinagar (+) (+) 3. Leh ( ) ( ) 4. NWH (+) (+) (c) Total monsoon precipitation 1. Shimla ( ) ( ) 2. Srinagar ( ) ( ) 3. Leh ( ) ( ) 4. NWH ( ) ( ) (+), increasing trend; ( ), decreasing trend. Significant at 95% confidence level. Table IV. Results of trend analysis of annual, winter and monsoon air temperatures in the NWH. Station Data span Trend analysis Mann Kendall s non-parametric test Linear regression coefficient b (a) Mean winter 1. Shimla (+) (+) 2. Srinagar (+) (+) 3. Leh (+) (+) 4. NWH (+) (+) (b) Mean monsoon 1. Shimla (+) (+) 2. Srinagar (+) (+) 3. Leh (+) (+) 4. NWH (+) (+) (c) Mean annual 1. Shimla (+) (+) 2. Srinagar (+) (+) 3. Leh (+) (+) 4. NWH (+) (+) (+), increasing trend; ( ), decreasing trend. significant at 95% confidence level. (Table III). In contrast, the monsoon and overall annual precipitation at Shimla and, consequently, the NWH have shown a decreasing trend (significant at 95% level of confidence) during this period. From the temperature point of view, analyses of the data show significant increasing trends in winter, monsoon and annual temperatures at all

5 CLIMATE CHANGE AND THE PRECIPITATION VARIATIONS IN THE NORTHWESTERN HIMALAYA 539 Figure 2. Linear trends in winter (a), monsoon (b) and annual precipitation (c) at Leh, Srinagar, Shimla and the NWH during the period (Pwin, Total winter precipitation; Pmon, Total monsoon precipitation; Pann, Total annual precipitation; Y, Time in years. Significant at 95% confidence level). Linear SPI. Figure 3. Temporal variation of winter (a), monsoon (b) and annual (c) SPI, Cramer s t statistic of SPI and standardized temperature index (STI) in the NWH during the period

6 540 M. R. BHUTIYANI ET AL. three stations in the NWH (only exception being the monsoon air temperature at Srinagar). Warming effect appears to be particularly significant during the winter season. The estimated rates of increase in temperature vary from about 0.06 C per decade in monsoon to about 0.14 C per decade in winter and C per decade in annual air temperature during this period ( ) (Figure 3). These values are marginally lower than those computed for a period of last century ( ) (Bhutiyani et al., 2007) when annual air temperature is estimated to have increased by about 0.16 C per decade, average winter temperature by 0.17 C per decade and the monsoon temperature by 0.09 C per decade. This difference could be attributed to an episode of comparatively higher (above average) temperatures from 1876 to 1892 which appears to have lowered the overall rate of increase. This episode was followed by three more periods of temperature variation. Below-average mean air temperature persisted from 1893 to 1939 indicating a cooler episode, followed by a period of relatively stable/average temperatures till around The periods from 1969 to 1990 and from 1991 till 2006 are characterized by above-normal temperatures indicating warmer episodes. Temperature seems to have increased at markedly different rates during these two periods. The rate of increase appears to be highest since 1991 as compared with the period before Seasonwise decade-to-decade rates of increase/ decrease of both the precipitation and temperature variations shown in Figure 4 confirm episodic variation in precipitation. It also shows that barring the decade of , the temperatures rose at a comparatively lower rate till This period was followed by a cooler episode of decreasing temperatures or insignificant rise. Increase in air temperature appears to have started in the decade of at a modest rate. With an exception of the decade of , it has continued to rise at all stations at a higher rate during the post-1991 period. The data on linear trends in monthly air temperatures during winter (Table V) in the last three decades shows that rate of increase has not been uniform through the winter. Although the beginning of winter (November) has shown an increasing, but statistically insignificant trend, the onset of spring (March) has been marked by substantial warming, being indicated by statistically increasing trend at four stations. 5. Discussion Contrary to the global estimate of increasing precipitation made by certain models (IPCC, 2001; Kripalani et al., 2001), majority of the studies on the long-term variation Figure 4. Seasonwise decade-to-decade rates of increase/decrease in standardized precipitation and temperature indices (SPI and STI) in the NWH. (a) Winter, (b) Monsoon and (c) Annual.

7 CLIMATE CHANGE AND THE PRECIPITATION VARIATIONS IN THE NORTHWESTERN HIMALAYA 541 Table V. Linear trends in monthly air temperatures during winters in the NWH in last two to three decades. Station Altitude in m Data span Months Nov Dec Jan Feb Mar Apr Bahang to (+) (+) (+) (+) (+) (+) Kanzalwan to (+) (+) (+) (+) (+) (+) Solang to (+) ( ) ( ) ( ) (+) (+) Gulmerg to (+) ( ) ( ) (+) (+) ( ) Dhundi to (+) (+) ( ) ( ) (+) (+) Haddan Taj to (+) (+) ( ) ( ) (+) ( ) Patseo to (+) (+) ( ) (+) ( ) ( ) (+), increasing trend; ( ) decreasing trend. significant at 95% confidence level. Table VI. Results of the power spectrum analysis of standardized precipitation index (SPI), standardized temperature index (STI) and standardized DTR index (S-DTR) of the northwestern Himalaya. Station Season SPI STI S-DTR Significant cycle in years Significant cycle in years Significant cycle in years 1. Shimla Winter 64, Monsoon 68,34,2.6 68,34,3.3 Annual 68,34,2.6, Srinagar Winter 3.1, Monsoon 29, 19.3, Annual 3.2,2.9, Leh Winter 58,29 Monsoon 8.3,2.3, Annual 58,29, NWH Winter 3.4, ,2.8 Monsoon 34,4.3,2.8, , ,2.8 Annual 34,9.7,2.7, ,2.8 Significant at 90% confidence level. Significant at 95% confidence level. Significant at 99% confidence level. in Indian summer monsoon rainfall (ISMR) have shown decreasing but insignificant trend over the Indian subcontinent and have pointed towards its random nature (Mooley and Parthasarathy, 1983; Pant et al., 1988; Thapliyal and Kulshrestha, 1991; Srivastava et al., 1992; Ahmed et al., 1996; Pant and Rupa Kumar, 1997). An overall decreasing trend in both depressions and cyclonic systems after the middle of 20th century may have been partly responsible for such behaviour (Bhaskar Rao et al., 2001; Singh, 2001). Since a large portion of summer precipitation in the NWH results from ISMR, the present study also shows a statistically significant decreasing trend (at 95% confidence level) in the monsoon and overall annual precipitation during the study period. In contrast, the winter precipitation has shown an increasing but statistically insignificant trend (at 95% confidence level). This is generally in good agreement with the results of other studies carried out in western parts of Himalayan foothills (Borgaonkar et al., 1996), Nepal Himalaya (Shreshtha et al., 2000) and in Upper Indus basin in the Karakoram Himalaya (Archer and Fowler, 2004). Absence of statistically significant trend in winter precipitation implies that either it may not have undergone any noticeable change during the study period or there must have been episodes of high and low precipitation periods to nullify the trend. The latter appears to be a distinct possibility as seen from variation in smoothed values of SPI in the plots of precipitation variation in different seasons (Figure 3). To study these variations in detail, existence of periodicity in these fluctuations was investigated. For this purpose, the SPI data of all the stations and the NWH of all the seasons were subjected to power spectrum analyses (Table VI). The oscillatory characteristics of the series are evident in the wide range of time periods obtained in their power spectra. They are also reflected in the plots of smoothed values of the NWH winter, monsoon and annual SPI series along with the Cramer s t statistic of Shimla, Srinagar and Leh (Figure 3). Based on these data, following episodes of winter and monsoon precipitation variation can be identified: 1. Winter precipitation (a) Period from 1866 to 1883 below average

8 542 M. R. BHUTIYANI ET AL. (b) Period from 1884 to 1911 above average (c) Period from 1912 to 1942 below average (c) Period from 1943 to 1964 above average (d) Period from 1965 to 1990 below average (e) Period from 1991 to 2006 above average 2. Monsoon precipitation (a) Period from 1866 to 1927 above average (b) Period from 1928 to 1942 below average (c) Period from 1943 to 1964 above average (d) Period from 1965 to 2006 below average It can be seen from the above data that during the period under study, episodes of above- and belowaverage winter and monsoon precipitation almost alternated each other with a periodicity varying from 20 to 60 years. The results of the power spectrum analyses of precipitation, temperature and DTR series confirm the presence of statistically significant periodicities ranging from 2.19 to 6.6 years and 29 to 68 years (Table VI). The period from 1943 to 1964 was the wettest with above-average precipitation values in both, monsoon as well as winter season. With regard to last few decades, it is seen that whereas monsoon precipitation has remained below average from 1965 to 2006, winter precipitation has been above average during the period between 1991 and Study of the trends in cumulative winter fresh snowfall depths (in cm) and temperature data (Table VII) of last three decades shows that out of seven stations, three stations namely; Bahang, Solang and Dhundi, show significant decreasing trends from 1991 to Incidentally, this period also coincides with relatively higher rates of increase in winter air temperature (Bhutiyani et al., 2007). Rising winter temperature appears to have affected the winter snowfall patterns too. Negative correlation coefficients are obtained in linear regression analyses between mean winter air temperature and total snowfall amounts (Figure 5) recordedatall meteorological stations on the windward side (Bahang, Solang, Dhundi) and only one station on the leeward side, i.e. Gulmerg of the Pir Panjal Himalayan Range in this period. Other stations, one on the leeward side of the Pir Panjal Himalaya, Haddan Taj, and two on windward and leeward sides of the Great Himalayan range (Kanzalwan and Patseo), do not show such effects. This demonstrates that the effect of rising temperatures on decreasing winter snowfall component in total winter precipitation is confined to the windward side of the Pir Panjal Range and to a lesser extent, some portions on the leeward side. This area falls in the Lower Himalayan snow-climatic zone (Sharma and Ganju, 2000) which is characterized by relatively lower altitudes, moderate to heavy snowfall with comparatively higher densities. The average temperatures being higher in this zone, snowfall exhibits wet characteristics. Other portions of the leeward side of the Pir Panjal Range and entire Greater Himalayan Range fall in the Middle Himalayan snow-climatic zone which receives low to moderate snowfall during winter months. In this zone, the altitudes are higher and temperatures are relatively lower than the Lower Himalayan snow-climatic zone (Mohan Rao et al., 1987), with snowfall exhibiting dry characteristics. Monthly air temperatures and snowfall amounts during winter months (Table VIII) show strong negative relationships for the months of November and March. Increasing temperatures during these two months, as seen in Table V, probably point towards late onset of winter and early advent of spring season, respectively, in the NWH in the last two to three decades. The date of onset of winter is taken as the day from which winter STI for that particular winter becomes negative. Similarly, the date of onset of spring is taken as the day when it starts assuming positive values of winter STI. Figure 6 gives a graphical display of the dates of onset of winter and spring seasons at two stations namely, Bahang in Lower Himalayan snow-climatic zone and Patseo in the Middle Himalayan snow-climatic zone. It can be seen from these graphs that in both zones, the onset of winter has been delayed by about 2 days per decade and onset of spring has been advanced by about 3 days per decade. This has effectively reduced the duration of winter and consequently the snowfall duration period by 5 6 days per decade and approximately by about 2 weeks in the last three decades. Archer and Fowler (2004) have also reported identical Table VII. The trends in winter precipitation (snowfall depth in cm) in the last three decades in the NWH and during a specific period between 1991 and Station Precipitation Temperature Trend (Period) Trend (Period) Trend (Period) Trend (Period) 1. Bahang ( ) ( ) ( ) ( ) (+) ( ) (+) ( ) 2. Solang ( ) ( ) ( ) ( ) (+) ( ) (+) ( ) 3. Dhundi ( ) ( ) ( ) ( ) (+) ( ) (+) ( ) 4. Gulmerg (+) ( ) ( ) ( ) (+) ( ) (+) ( ) 5. Haddan Taj ( ) ( ) ( ) ( ) (+) ( ) (+) ( ) 6. Kanzalwan ( ) ( ) (+) ( ) (+) ( ) ( ) ( ) 7. Patseo ( ) ( ) ( ) ( ) (+) ( ) (+) ( ) (+), increasing trend; ( ), decreasing trend. Significant at 95% confidence level.

9 CLIMATE CHANGE AND THE PRECIPITATION VARIATIONS IN THE NORTHWESTERN HIMALAYA 543 Figure 5. Relationship between the cumulative winter snowfall depth in cm and winter mean air temperature in last three decades at some meteorological stations in the NWH. Stations: Solang (a), Bahang (b), Dhundi (c) and Gulmerg (d), which are on the windward side of Pir Panjal Himalaya, show negative relationship whereas stations Kanzalwan (e), Patseo (f) and Haddan Taj (g), which are on the leeward side of Pir Panjal Range and windward side of Great Himalaya show no such relationship. (Sw, Cumulative winter snowfall depth in cm; Tw, Winter mean air temperature in C; r 2 = Correlation coefficient; Significant at 95% confidence level). results from studies in Upper Indus basin in Karakoram Himalaya. Studies in Nagaoka, Japan (Nakamura and Shimizu, 1996), on winter snowfall patterns during eight winters from to have made similar observations. This has been attributed to the effect of global warming in the last two decades in Japan and increasing spring temperature trends over Eurasia in the last century. Studies on snow cover variability in the Swiss Alps where the mean snow depth, the duration of continuous snow cover and number of snowfall days have also shown a gradual increase from 1931 till early 1980s and significant decrease thereafter, indicating that the winter precipitation to an increasing degree now falls in the form of rain instead of snow (Beniston, 1997; Laternser and Schneebeli, 2003). In Bulgarian mountainous region, although long-term decreasing trend, linked to climatic warming, has been noticed in winter precipitation over a period of 70 years ( ), the snow cover has exhibited significant evidence of decadalscale variability and the period between 1971 and 2000

10 544 M. R. BHUTIYANI ET AL. Table VIII. Relationships between snowfall amounts and monthly average temperature. Station Altitude in m Data span Months Nov Dec Jan Feb Mar Apr Bahang to ( ) ( ) ( ) ( ) ( ) NSR Kanzalwan to ( ) (+) ( ) (+) ( ) (+) Solang to ( ) ( ) (+) ( ) ( ) NSR Gulmerg to ( ) ( ) ( ) ( ) ( ) ( ) Dhundi to ( ) ( ) ( ) ( ) ( ) ( ) Haddan Taj to ( ) ( ) (+) ( ) ( ) ( ) Patseo to ( ) ( ) ( ) (+) ( ) (+) (+), increasing trend; ( ), decreasing trend; NSR, no snowfall recorded. Significant at 95% confidence level. Figure 6. Temporal variations in dates of onset of winter and spring seasons at two stations namely, Bahang (a) in Lower Himalayan snow-climatic zone and Patseo (b) in the Middle Himalayan snow-climatic zone in the NWH. was marked by significant trend towards a late start of the snowfall season (Petkova et al., 2004; Brown and Petkova, 2007). Temporal variation of Eurasian snow cover area (ESCA) in March (Brown, 1997, 2002) and winter mean air temperature in the NWH (Figure 7) demonstrates no significant trend in the variation of ESCA from 1922 till late 1960s. Consequent decrease in ESCA, thereafter, is marked by a period of rapidly increasing winter air temperatures in the NWH, indicating a direct inverse relationship between these two parameters Precipitation variation and global teleconnections While the influence of El Ninõ Southern Oscillations (ENSO) related meteorological phenomenon on ISMR in the Peninsular India is reasonably well understood (Pant et al., 1988; Reddy et al., 1989; Bhalme et al., 1990; Kane, 1998), limited efforts have been made to establish any influence they may have on the precipitation in the NWH (Shreshtha et al., 2000). Since the winter precipitation in the NWH occurs under the influence of westerly disturbances, originating from the Mediterranean and the Caspian Sea or the Atlantic, the precipitation variation in the NWH may be related to the shifts in the NAO index (North Atlantic Oscillation Index) (Jones et al., 1997; Archer and Fowler, 2004). The present study has examined such teleconnections between winter and monsoon precipitation in the NWH and the meteorological phenomenon related to ENSO and NAO measured in terms of SOI and NAO Indices, respectively (Table IX).

11 CLIMATE CHANGE AND THE PRECIPITATION VARIATIONS IN THE NORTHWESTERN HIMALAYA 545 Figure 7. Temporal variation of standardized Eurasian snow cover area (ESCA) (March) (Data source Brown, 2002) and winter STI in the NWH during the period (An onset of period of increase in winter air temperature and decrease in ESCA is indicated by a solid black arrow). Table IX. Correlation between the monthly average winter NAO and monsoon SOI indices and winter and monsoon precipitation and temperature in the NWH. Station Winter Monsoon (summer) NAO index SOI index NAO index OI index (a) Precipitation 1. Shimla Srinagar Leh NWH (b) Temperature 1. Shimla Srinagar Leh NWH Significant at 95% confidence level. The results show statistically insignificant relationships between the temperature variation in the NWH in the late 19th and 20th centuries in winter and monsoon seasons and the respective NAO and SOI indices. Winter precipitation in the NWH, as a whole, has a statistically significant (at 95% confidence level) relationship with the monthly average winter NAO index, indicating reasonably strong teleconnections between the two. Similar findings have been reported by Archer and Fowler (2004) for the winter precipitation in the UIB in the Karakoram Himalaya. Statistically insignificant correlation between winter precipitation in the NWH and monthly average winter SOI index indicates limited impact of southern oscillations on winter precipitation in the NWH. On the contrary, monsoon precipitation is significantly correlated with monthly average monsoon SOI, indicating strong influence southern oscillations have on variations in monsoon precipitation in the NWH. Statistically insignificant correlations between the monsoon NAO and monsoon precipitation do not conclusively suggest any influence, NAOs may have on monsoon precipitation in the NWH or this may also mean that westerly weather during monsoon months brings dryness, perhaps providing a blocking effect on monsoon moisture incursions into the high mountain Karakoram region (Archer and Fowler, 2004). A positive and statistically significant relationship between the ENSO linked monsoon SOI and monsoon precipitation confirm dynamic teleconnections between these two phenomena in Peninsular India (Bhalme et al., 1990; Kane, 1998; Shreshtha et al., 2000) and also in the NWH region (Fowler and Archer, 2005). Significant periodicity of 2.2 to 4.3 years in power spectrum analyses of the precipitation series (Table VI) appears to correspond to the influence of the stratospheric quasibiennial oscillations (QBO) and ENSO-related meteorological phenomenon. Similarly, periodicity on the decadal scale ( years) corresponds to the solar forcing related to double sunspot cycles (Hale), indicating their influence on the decadal and multi-decadal scale (Bhalme and Mooley, 1981; Bhalme et al., 1990; Ananthakrishnan and Parthasarathy, 1984; Reddy et al., 1989; Ogurtsov et al., 2002; Agnihotri and Dutta, 2003; Solanki et al., 2004). On the lower frequency range, tri- to multi-decadal variability, related to sunspot activity, is revealed in a comparatively strong periodicity between 29 and 34 years and between 58 and 64 years at Shimla and Leh (significant at 99% confidence level). Epochal behaviour of the precipitation appears to have ensured presence of comparatively cooler and warmer periods, although the temperature continued to increase from the beginning of the last century. The periods of excess (deficient) annual precipitation, with overall

12 546 M. R. BHUTIYANI ET AL. Figure 8. Relationship between (a) Winter (b) Monsoon and (c) Annual SPI, STI and standardized diurnal temperature range (S-DTR) in the NWH. increase (or decrease) in cloud cover, were associated with lower (higher) temperature, because of the decrease (increase) in net radiation balance. A remarkable aspect of the climate change in the NWH is that these teleconnections appear to have weakened considerably in the last three decades, i.e. after the late-1960s (Figure 8) (Krishna Kumar et al., 1999; Bhutiyani et al., 2007). Similar findings on the global scale, indicating a significant shift in global atmospheric circulation and climate, have been reported. This shift has been attributed to rapid increase in anthropogenic aerosol emissions and reduction in northward oceanic heat flux associated with the North Atlantic thermohaline circulation in the 1950s 1970s (Baines and Folland, 2007). 6. Summary and conclusions 1. The trend analyses indicate an increasing but statistically insignificant trend (at 95% confidence level) in winter precipitation in the NWH and statistically significant (95% level of confidence) decreasing trend in monsoon and overall annual precipitation and during the study period The oscillatory/episodic characteristics of the precipitation series are reflected in wide range of time periods obtained in their power spectra. Temperature data show significant increasing trends in winter, monsoon and annual temperatures. Warming effect appears to be particularly significant during the winter season.

13 CLIMATE CHANGE AND THE PRECIPITATION VARIATIONS IN THE NORTHWESTERN HIMALAYA Effect of global warming is evident on decreasing winter snowfall component in total winter precipitation on the windward side and some portions of the leeward side of the Pir Panjal Range since 1991, leading to delay in onset of winter and early spring and effective reduction during the snowfall period. Rest of the Himalayas does not appear to have undergone any significant change in the snowfall pattern. 3. Precipitation fluctuations in the NWH appear to be strongly affected by global teleconnections (NAO during winter months and SOI during the monsoon months), which are also related to stratospheric QBO, ENSO and sunspot activity on tri-decadal to multidecadal scales. These teleconnections appear to have weakened considerably in the last three decades, i.e. after the late-1960s. This may be because of rapid increase in anthropogenic aerosol emissions. Acknowledgements The authors are thankful to Defence R & D Organization HQ, New Delhi for providing funds for the research project and the Commandant CME, and Commander, Faculty of Civil Engineering, CME for their support. The authors are thankful to the Director, India Meteorological Department (IMD), Director, Snow and Avalanche Study Establishment (SASE), Manali and Director, Indian Institute of Tropical Meteorology, Pune for providing the data. The authors are particularly indebted to Dr H P Borgaonkar and Dr A A Munot for their help in analysis of the data. The authors are also grateful to two anonymous reviewers for their critical review and useful comments on the paper. References Agnihotri R, Dutta K Centennial scale variations in monsoonal rainfall (Indian, east equatorial and Chinese monsoons): manifestations of solar variability. Current Science 85: Ahmed ASMS, Minum AA, Begum QN El-Niño southern oscillation and rainfall variation over Bangladesh. Mausam 47: Ananthakrishnan R, Parthasarathy B Indian rainfall in relation to the sunspot cycle: Journal of Climatology 4: Archer DR, Fowler HJ Spatial and temporal variations in precipitation in the Upper Indus Basin, global teleconnections and hydrological implications. Hydrology and Earth System Sciences 8(1): Baines PG, Folland CK Evidence for rapid global climate shift across the late 1960s. Journal of Climate 20: Beniston M Variation of snow depth and duration in the Swiss Alps over the last 50 years: Links to changes in large-scale climatic forcings. Climatic Change 36: Beniston M, Diaz FD, Bradley RS Climatic change at high elevation sites: an overview. Climatic Change 36: Beniston M Climatic change in mountainous regions: a review of possible impacts. Climatic Change 59: Bhalme HN, Mooley DA Cyclic fluctuations in the flood area and relationship with double (Hale) sunspot cycle. Journal of Applied Meteorology 20: Bhalme HN, Sikdar AB, Jadhav SK Relationships between planetary scale waves, Indian monsoon rainfall and ENSO. Mausam 41: Bhaskar Rao DV, Naidu CV, Sriniwasa Rao BR Trends and fluctuations of the cyclonic systems over North Indian Ocean. Mausam 52: Bhutiyani MR Avalanche problems in Nubra and Shyok valleys in Karakoram Himalaya, India. Journal of Institution of Military Engineers of India 3: 3 5. Bhutiyani MR, Kale VS, Pawar NJ Long-term trends in maximum, minimum and mean annual air temperatures across the northwestern Himalaya during the 20th century. Climatic Change 85: Blackman RB, Turkey JW The Measurement of Power Spectra, Dover Publication Inc.: New York; 190. Borgaonkar HP, Pant GB, Rupa Kumar K Ring-width variations in Cedrus deodara and its climatic response over the western Himalaya. International Journal of Climatology 16: Borgaonkar HP, Pant GB Long-term climate variability over monsoon Asia as revealed by some proxy sources. Mausam 52: Brown RD Historical variability in North Hemisphere spring snow covered area. Annals of Glaciology 25: Brown RD Reconstructed North American, Eurasian, and Northern Hemisphere Snow Cover Extent, National Snow and Ice Data Center, Digital media: Boulder; CO. Brown RD, Petkova N Snowcover variability in Bulgarian mountainous regions. International Journal of Climatology 27: Crowley TJ Causes of climate change over the past 1000 years. Science 289: Diaz HF, Bradley RS Temperature variations during the last century at high elevation sites. Climatic Change 36: Diaz HF, Grosjean M, Graumlich L Climate variability and change in high elevation regions: past, present and future. Climatic Change 59: 1 4. De US, Mukhopadhyay RK Severe heat wave over the Indian subcontinent in 1998, in perspective of global climate. Current Science 75: Easterling DR, Horton B, Jones PD, Peterson TC, Karl TR, Parker DE, Salinger JM, Razuvzyev V, Plummer N, Jamason P, Folland CK Maximum and minimum temperature trends for the globe. Science 227: Ellsaesser HW, MacCracken MC, Walton JJ, Grotch SL Global climatic trends as revealed by recorded data. Reviews of Geophysics 24: Fallot JM, Barry RG, Hoogstrate D Variation of mean cold season temperature, precipitation and Snow depths during the last 100 years in the former depths during the last 100 years in the former Soviet Union (FSU). Hydrological Sciences-Journal 42: Fowler HJ, Archer DR Hydro-climatological variability in Upper Indus Basin and implications for water resources. In: Wagner, T. et al., (eds.) Regional Hydrological Impacts of Climate Change Impact Assessment and Decision Making. Proceedings of Symposium S6 held during the Seventh IAHS Scientific Assembly at Foz do lguacu, Brazil, IAHS Publication 295, pp Fowler HJ, Archer DR Conflicting signals of climatic change in the upper Indus Basin. Journal of Climate 19: IPCC Climate Change. The IPCC Third Assessment Report, Vol. I, The Scientific basis, II-Impacts, Adaptation and Vulnerability, III- Mitigation, Cambridge University Press: Cambridge and New York. IPCC Climate Change 2007: Climate Change Impacts, Adaptation and Vulnerability, Working Group II Contribution to the Intergovernmental Panel on Climate Change Fourth Assessment Report Summary for Policymakers. Jones PD, Raper SCB, Bradley RS, Diaz HF, Kelly PM, Wigley TMC. 1986a. Northern Hemispheric surface air variation: Journal of Climatology and Applied Meteorology 25: Jones PD, Raper SCB, Bradley RS, Diaz HF, Kelly PM, Wigley TMC. 1986b. Southern Hemispheric surface air variation: Journal of Climatology and Applied Meteorology 25: Jones PD, Jonsson T, Wheeler D Extension to the North Atlantic oscillation using early instrumental pressure observations from Gibraltar and south-west Iceland. International Journal of climatology 17: Kane PR El Niño, southern oscillation, equatorial eastern Pacific sea surface temperatures and summer monsoon rainfall in India. Mausam 49: Karl TR, Knight RW, Plummer N Trends in high frequency climate variability in the twentieth century. Nature 377: Kendall MG, Stuart A The advance theory of Statistics, Vol. 2. Hafner Publishing Co.: New York, USA. Knappenberger PC, Michaels PJ, Davis RE Nature of observed temperature changes across the United States during the 20th century. Climatic Research 17:

14 548 M. R. BHUTIYANI ET AL. Kripalani RH, Kulkarni A, Sabade SS El Niño Southern Oscillation, Eurasian snow cover and the Indian monsoon rainfall. PINSA 67 A: Krishna Kumar K, Rajgopalan B, Cane MK On the weakening relationship between the Indian monsoon and ENSO. Science 284: Laternser M, Schneebeli M Long-term snow climate trends of the Swiss Alps ( ). International Journal of Climatology 23: Liu X, Chen H Climatic warming in the Tibetan plateau during recent decades.international Journal of Climatology 20: Ma Y, Zhong L, Su Z Determination of regional distributions and seasonal variations of land surface heat fluxes from Landsat 7 enhanced thematic mapper data over the central Tibetan plateau area. Journal of Geophysical Research-Atmospheres 111: D DOI: /2005JD Mitchell JM ( Jr), Dzerdzeevskii B, Flohn H, Hofmeyr WL, Lamb HH, Rao KN, Wallen CC WMO Technical Note No. 79, World Meteorological Organization, Geneva. Mohan Rao N, Rangachary N, Kumar V, Verdhan A Some aspects of snow cover development and avalanche formation in Indian Himalaya. Proceedings of Davos Symposium on Avalanche Formation, Movement and Effects. IAHS Publication No. 162, Mooley DA, Parthasarathy B Indian summer monsoon and El Niño. Pageoph 121: Mutreja KN Applied Hydrology. Tata McGraw Hill Publishing Company Limited: New Delhi. Nakamura T, Shimizu M Variation of snow, winter precipitation and winter air temperature during the last century at Nagaoka, Japan. Journal of Glaciology 42: Ogurtsov MG, Nagovitsyn YA, Kocharov GE, Jungner H Longperiod cycles of the Sun s activity recorded in direct solar data and proxies. Solar Physics 211: Oerlemans J Quantifying global warming from retreat of glaciers. Science 264: Pant GB, Borgaonkar HP Climate of the hill regions of Uttar Pradesh. Himalayan Research and Development 3: Pant GB, Rupa Kumar K, Parthasarathy B, Borgaonkar HP Long-term variability of the Indian summer monsoon and related parameters. Advances in Atmospheric Sciences 5: Pant GB, Rupa Kumar K Climates of South Asia: Behaviour Studies in Climatology. John Wiley and Sons: West Sussex, England; Petkova N, Koleva E, Alexandrov V Snowcover variability and change in mountainous regions of Bulgaria, Meteorologische Zeitschrift 13: Qiang F, Celeste MJ, Stephen GW, Dian JS Contribution of stratospheric cooling to satellite inferred tropospheric temperature trends. Nature 429: Rakhecha PR, Kulkarni AK, Mandal BN, Dhar ON Winter and spring precipitation over the northwestern Himalaya. Proceedings of the First National Symposium on Seasonal Snow Cover, New Delhi, Rebetez M Summer 2003 maximum and minimum daily temperature over a 3300 m altitudinal range in the Alps. Climate Research 27: Reddy RS, Neralla VR, Godson WL The solar cycle and Indian rainfall. Theoretical and Applied Climatology 39: SASE Snow Meteorological data of Western Himalaya Vol. 1. Snow and Avalanche Study Establishment, Manali, India. Schaer C, Vidale PL, Luthi D, Frei C, Haberli C, Liniger MA, Appenzeller C The role of increasing temperature variability in European summer heat waves. Nature 427: Seko K, Takahashi S Characteristics of winter precipitation and its effects on glaciers in Nepal Himalaya. Bulletin of Glacier Research 9: Sharma KP, Moore B, Vorosmarty CJ III Anthropogenic, climatic and hydrologic trends in the Kosi Basin, Himalaya. Climate Change 47: Sharma SS, Ganju A Complexities of avalanche forecasting in western Himalaya an overview. Journal of CRST 31: Shreshtha AB, Wake CP, Dibb JE, Mayewski PA Precipitation fluctuations in the Nepal Himalaya and its vicinity and relationship with some large-scale climatological parameters. International Journal of Climatology 20: Singh OP Long-term trends in the frequency of monsoonal cyclonic disturbances over the north Indian Ocean. Mausam 52: Singh N, Sontakke NA On climatic fluctuations and environmental changes of the Indo-Gangetic Plains, India. Climatic Change 52: Solanki SK, Usoskin IG, Kromer B, Schüssler M, Beer J Unusual activity of the Sun during recent decades compared to the previous 11,000 years. Nature 431: s Srivastava HN, Dewan BN, Dikshit SK, Prakasha Rao GS, Singh SS, Rao KR Decadal trends in climate over India. Mausam 43: Thapliyal V, Kulshrestha SM Decadal changes and trends over India. Mausam 42: Villaba R, Lara A, Boninsegna JA, Masiokas M, Delgado S, Aravena JC, Roig FA, Schmelter A, Wolodarsky A, Ripalta A Largescale temporal changes across the southern Andes: 20th century variations in the context of the past 400 years. Climatic Change 59: Vinnikov K, Graisman PYa, Lugina KM Empirical data on contemporary global climatic changes (Temperature and Precipitation). Journal of Climate 3: Vuille M, Bradley RS, Werner M, Keimig F th Century climate change in the tropical Andes: observations and model results. Climatic Change 59: Wibig J, Glowicki B Trends in minimum and maximum temperature in Poland. Climate Research 20: Yadav RR, Park Won-Kyu, Singh J, Dubey B Do the western Himalaya defy global warming? Geophysical Research Letters 31: L Zhai P, Sun A, Ren F, Xiaonin L, Gao B, Zhang Q Changes in climate extreme in China. Climate Change 42: