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The Sikkim region of the Himalayas is among one of the most highly sensitive hotspots to climate change due to its fragile mountainous environment and rapidly growing population, which exert significant impacts on regional ecosystem factors, including biodiversity and hydrology. Limited observational data coverage in space and time for the high-altitude mountainous region impedes our understanding of climate change and its impact on the environment. In this paper, we develop a 437-year tree-ring width index chronology of Tsuga dumosa (D.Don) Eichler in northern Sikkim as a climate proxy. The substantial dendroclimatic potential of this proxy is evidenced in various statistics computed from the tree-ring chronology. An analysis of the tree-ring chronology indicates a strong negative relationship between late-summer mean temperatures (July–August–September; JAS) and tree growth. This relationship enables us to reconstruct the JAS mean temperature over northern Sikkim since 1705 C.E. The 304-year (1705–2008 C.E.) reconstructed temperature series shows similar warm and cool epochs, which have been observed in many other temperature reconstructions in the region and other proxy records of glacial fluctuations. An overall steady decreasing trend in the regional surface temperature is observed since 1705 C.E., while an increasing trend with intermittent, short and cool epochs are noticed from 1850 C.E. to the present. Prior to the observational period (before 1901 C.E.), cold conditions (X - 1σ) prevailed during 1816–1819, 1831–1837, 1856–1859, and 1884–1887 C.E, with extremely cold conditions (X - 2σ) occurring in 1816, 1817, 1832, 1833, 1857, 1877, 1884, and 1885 C.E; Warm conditions (X + 1σ) prevailed during 1713–1735 and 1823–1827 C.E, with extremely warm (X + 2σ) conditions occurring in 1724, 1823, 1824, and 1825 C.E. Global teleconnections of the reconstructed temperature variations indicate the important roles of the Pacific Decadal Oscillation (PDO), El Nino Southern Oscillation (ENSO), and volcanic eruptions as drivers of temperature variations in the Sikkim region of the Himalayas.

Indian monsoon (June–September) and post monsoon (October–November) rainfall show a distinct trend from coast to inland primarily due to moisture availability. However, the response of this synoptic-scale variation of rainfall amount to annual ring growth of Indian teak has not been studied systematically yet. The study is important as (1) ring width of Indian teak is considered as a reliable proxy for studying monsoon climate variability in multi-centennial time scale and (2) observed meteorological data show systematic changes in rainfall variation from coast to inland since last three decades. Towards this, we present here tree-ring width data from two locations—Thatibanda (1747–1979) and Nagzira (1728–2000) and use similar published data from two other locations—Allapalli (1866–1897) and Edugurapalli (1827–2000). The locations fall along a southeast northwest transect from south east Indian coast to inland. Monthly mean data from nearest observatories show an increasing trend in monsoon rainfall and a pronounced decreasing trend in post monsoon rainfall towards inland. Ring width data show moderately positive response to monsoon rainfall and negative response to summer (March–May) temperature for all stations suggesting moisture deficit in hot summer and intense precipitation in monsoon affect ring growth pattern in different ways. Ring width indices also exhibit significantly positive response with post monsoon rainfall at coastal location. The response gradually reduces towards inland. This preliminary study, thus, suggests that Indian teak has a potential to capture signals of the synoptic variation of post monsoon rainfall from coast to inland.

Inter and intra-annual carbon isotope compositions (δ 13 C) of several annual growth rings of teak trees from two monsoonal regimes from India were studied and compared with the corresponding oxygen isotopic (δ 18 O) variations. In teak from both the regimes, amplitudes of intra-annual δ 13 C were ∼2-3 times lower than that observed in δ 18 O. Seasonal cycle with lower δ 13 C values at the middle and higher at ring boundaries was observed for teak from central India, dominated by the southwest monsoon. Positive correlations of intra-annual δ 13 C values with the corresponding δ 18 O values of the same rings and with relative humidity (RH) of the concurrent period suggest a dominant role of RH in controlling δ 13 C values of teak from central India. Intra-annual δ 13 C variations of teak from southern India, receiving both the southwest and northeast monsoons, revealed an initial decreasing trend followed by an increasing trend before culminating in depleted 13 C values at the end of the growing season. No correlation was observed between intra-annual δ 13 C and δ 18 O variations of teak trees from southern India. Regional differences in the climatology of δ 13 C of atmospheric CO 2 or the lengths of growing season could be likely reasons for differing intra-annual δ 13 C variations of teak from the two climatic regimes.

Proxy-based reconstructions have indicated that the South Asian summer monsoon (SASM) has shown interannual- to centennial-scale oscillations over the past millennium; however, the variability and mechanisms that operate over different timescales remain to be explicitly identified. This is firstly because of the inadequate spatial representation within previous SASM reconstructions, which is caused by the scarcity of tree-ring records from the core monsoon region. This study used eight additional Indian tree-ring width chronologies from the core region of the SASM to update the reconstructed SASM index that covers the past 1105 years. We found that the most significant interannual variability of SASM is mainly related to the El Nino–Southern Oscillation (ENSO) over the past few hundred years. The decadal/multidecadal oscillations show a high negative/positive correlation with the Pacific Decadal Oscillation (PDO)/Atlantic Multidecadal Oscillation (AMO) after the late 19th century. The centennial component of the SASM, which accounts for 19.4% of the total variance, begins to weaken from the mid-13th century and reaches a minimum in the mid-15th century. The component gradually strengthens again to reach its peak in the early 17th century, followed by a decline trend toward recent. The centennial variations agree well with historical changes in solar activity before the nineteenth century that caused changes in land–sea thermal contrast. However, the close linkage between the SASM and solar activity has weakened since the Industrial era, probably because of the enhanced influence of anthropogenic aerosol emissions.

We present here a rationale for estimation of soil water oxygen isotope values ( δ sw ) from tree ring cellulose oxygen isotope data and examine, for the first time, its ( δ sw ) efficacy as a tool to obtain paleoclimate information. We analyzed pre-dated tree ring cellulose samples collected from a site at Western Himalaya for oxygen isotopes, used similar dataset of overlapping time period from 12 different locations across the world, reconstructed δ sw for 1901–2004 CE, compared the data with available observations and examined implications of this technique. Our study shows (a) good agreement in spatial ranges between observed and estimated δ sw data suggesting its suitability for a representative parameter, and (b) reconstructed δ sw largely depend on soil moisture content modulated by regional evaporation regimes. Considering a growing importance of measurement of recycled soil moisture and its ensuing role in rainfall amount, a method to reconstruct soil moisture isotope as presented in this work will enable application of land hydrological models to the past.

In this chapter, we discuss climate variability over the Western Himalaya based on instrumental records as well as information derived from tree-ring data. We focus here on two important climatological elements, namely rainfall and temperature of Western Himalayan region. Trend analyses of rainfall based on 14 stations covering entire western Himalayan region from Kashmir to Uttarakhanda indicate different patterns of rainfall variability. The database does not show any coherent patterns among the stations and does not indicate any significant trend during the twentieth century. Data on temperature show overall warming mainly contributed by maximum temperature. Most of the stations indicate significant increasing trends in maximum temperature for all the seasons. Cooling trend is observed mostly in minimum temperature of some stations for different seasons. Annual maximum, minimum and mean temperature series of all the stations indicate significant warming except slight cooling in minimum temperature of Deheradun, Mukteswar and Mussoorie. Climate projections for twenty-first century also indicate warming over the entire Himalayan region with significant warming in Tibetan plateau, and increasing trend in summer precipitation over the central Himalayan region including Nepal and Tibetan Plateau.

Past global climate changes had strong regional expression. To elucidate their spatio-temporal pattern, we reconstructed past temperatures for seven continental-scale regions during the past one to two millennia. The most coherent feature in nearly all of the regional temperature reconstructions is a long-term cooling trend, which ended late in the nineteenth century. At multi-decadal to centennial scales, temperature variability shows distinctly different regional patterns, with more similarity within each hemisphere than between them. There were no globally synchronous multi-decadal warm or cold intervals that define a worldwide Medieval Warm Period or Little Ice Age, but all reconstructions show generally cold conditions between AD 1580 and 1880, punctuated in some regions by warm decades during the eighteenth century. The transition to these colder conditions occurred earlier in the Arctic, Europe and Asia than in North America or the Southern Hemisphere regions. Recent warming reversed the long-term cooling; during the period AD 1971?2000, the area-weighted average reconstructed temperature was higher than any other time in nearly 1,400 years. Fil: Ahmed, Moinuddin. Federal Urdu University of Arts, Science and Technology. Department of Botany; Pakistán Fil: Anchukaitis, Kevin J.. Columbia University. Lamont Doherty Earth Observatory; Estados Unidos. Woods Hole Oceanographic Institution; Estados Unidos Fil: Asrat, Asfawossen . Addis Ababa University. School of Earth Sciences; Etiopía Fil: Borgaonkar, Hemant P.. Indian Institute of Tropical Meteorology; India Fil: Braida, Martina . University of Trieste. Dipartimento di Matematica e Geoscienze; Italia Fil: Buckley, Brendan M. . Columbia University. Lamont Doherty Earth Observatory; Estados Unidos Fil: Ulf Büntgen. Swiss Federal Research Institute WSL; Suiza Fil: Chase, Brian M.. Université Montpellier. Département Paléoenvironnements et Paléoclimats (PAL); Francia. University of Bergen. Department of Archaeology, History, Cultural Studies and Religion; Noruega Fil: Christie, Duncan A. . Universidad Austral de Chile. Laboratorio de Dendrocronología y Cambio Global; Chile. Universidad de Chile. Center for Climate and Resilience Research; Chile Fil: Cook, Edward R.. Columbia University. Lamont Doherty Earth Observatory; Argentina Fil: Curran, Mark A. J.. Australian Antarctic Division; Australia. University of Tasmania. Antarctic Climate & Ecosystems Cooperative Research Centre; Australia Fil: Diaz, Henry F. . National Oceanic and Atmospheric Administration. Cooperative Institute for Research in Environmental Sciences, ; Estados Unidos Fil: Esper, Jan. Johannes Gutenberg University. Department of Geography,; Alemania Fil: Fan, Ze-Xin . Chinese Academy of Sciences. Xishuangbanna Tropical Botanical Garden ; China Fil: Gaire, Narayan P. . Nepal Academy of Science and Technology. Faculty of Science,; Nepal Fil: Ge, Quansheng. Chinese Academy of Sciences. Institute of Geographical Sciences and Natural Resources Research, ; China Fil: Gergis, Joëlle. University of Melbourne. School of Earth Sciences; Australia Fil: González-Rouco, J Fidel. Universidad Complutense de Madrid. Departamento Astrofísica y CC de la Atmósfera; España Fil: Goosse, Hugues. Université Catholique de Louvain. LemaitreCenter for Earth and Climate Research, Earth and Life Institute; Bélgica Fil: Grab, Stefan W. . University of the Witwatersrand. School of Geography,Archaeology and Environmental Studies; Sudáfrica Fil: Graham, Nicholas. Hydrologic Research Center; Estados Unidos Fil: Graham, Rochelle . Hydrologic Research Center; Estados Unidos Fil: Grosjean, Martin . University of Bern. Oeschger Centre for Climate Change Research & Institute of Geography; Suiza Fil: Hanhijärvi, Sami T.. University of Helsinki. Department of Environmental Sciences; Finlandia Fil: Kaufman, Darrell S.. Northern Arizona University. School of Earth Sciences and Environmental Sustainability; Estados Unidos Fil: Kiefer, Thorsten . International Project Office, Past Global Changes (PAGES); Suiza Fil: Kimura, Katsuhiko. Fukushima University. Department of Symbiotic System Science; Japón Fil: Korhola, Atte A.. University of Helsinki. Department of Environmental Sciences; Finlandia Fil: Krusic, Paul J.. Stockholm University. Department of Physical Geography and Quaternary Geology; Suecia Fil: Lara, Antonio. Universidad Austral de Chile. Laboratorio de Dendrocronología y Cambio Global; Chile. Universidad de Chile. Center for Climate and Resilience Research; Chile Fil: Lézine, Anne-Marie. Université Pierre et Marie Curie. Laboratoire d’Océanographie et du Climat: Expérimentations et Approches Numériques (LOCEAN); Francia Fil: Ljungqvist, Fredrik C.. Stockholm University. Department of History, ; Suecia Fil: Lorrey, Andrew M.. National Institute of Water and Atmospheric Research Ltd., National Climate Centre Auckland; Nueva Zelanda Fil: Luterbacher, Jürg. Justus Liebig University. Department of Geography, Climatology, Climate Dynamics and Climate Change; Alemania Fil: Masson-Delmotte, Valérie . Laboratoire des Science du Climat et de l’Environnement, Gif-sur-Yvette; Francia Fil: McCarroll, Danny. Swansea University. Department of Geography; Reino Unido Fil: McConnell, Joseph R.. Nevada System of Higher Education. Desert Research Institute; Estados Unidos Fil: McKay, Nicholas P.. Northern Arizona University. School of Earth Sciences and Environmental Sustainability; Estados Unidos Fil: Morales, Mariano Santos. Consejo Nacional de Investigaciones Científicas y Técnicas. Científico Tecnológico Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentina Fil: Moy, Andrew D.. Australian Antarctic Division; Australia. University of Tasmania. Antarctic Climate & Ecosystems Cooperative Research Centre; Australia Fil: Mulvaney, Robert. British Antarctic Survey; Reino Unido Fil: Mundo, Ignacio Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Científico Tecnológico Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentina Fil: Nakatsuka, Takeshi. Nagoya University. Department of Earth and Environmental Sciences; Japón Fil: Nash, David J.. University of the Witwatersrand. School of Geography,Archaeology and Environmental Studies; Sudáfrica. University of Brighton. School of Environment and Technology; Reino Unido Fil: Neukom, Raphael . Swiss Federal Research Institute WSL; Suiza Fil: Nicholson, Sharon E.. Florida State University. Department of Earth, Ocean and Atmospheric Sciences, ; Estados Unidos Fil: Oerter, Hans. Alfred Wegener Institute for Polar and Marine Research in the Helmholtz Association. Department of Glaciology; Alemania Fil: Palmer, Jonathan G.. University of Exeter. College of Life and Environmental Sciences; Reino Unido. University of New South Wales. Climate Change Research Centre; Australia Fil: Phipps, Steven J.. University of New South Wales. Climate Change Research Centre; Australia. University of New South Wales. ARC Centre of Excellence for Climate System Science; Australia Fil: Prieto, Maria del Rosario. Consejo Nacional de Investigaciones Científicas y Técnicas. Científico Tecnológico Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentina Fil: Rivera, Andres. Centro de Estudios Cientificos; Chile Fil: Sano, Masaki. Nagoya University. Department of Earth and Environmental Sciences; Japón Fil: Severi, Mirko. University of Florence. Department of Chemistry ‘Ugo Schiff’; Italia Fil: Shanahan, Timothy M.. University of Texas at Austin. Jackson School of Geosciences; Estados Unidos Fil: Shao, Xuemei. Chinese Academy of Sciences. Institute of Geographical Sciences and Natural Resources Research; China Fil: Shi, Feng. Chinese Academy of Sciences. LASG, Institute of Atmospheric Physics, ; China Fil: Sigl, Michael . Nevada System of Higher Education. Desert Research Institute,; Estados Unidos Fil: Smerdon, Jason E.. Columbia University. Lamont Doherty Earth Observatory; Estados Unidos Fil: Solomina, Olga N. . Russian Academy of Sciences. Institute of Geography; Rusia Fil: Steig, Eric J.. University of Washington. Department of Earth and Space Sciences; Estados Unidos Fil: Stenni, Barbara. University of Trieste. Dipartimento di Matematica e Geoscienze; Italia Fil: Thamban, Meloth. National Centre for Antarctic and Ocean Research; India Fil: Trouet, Valerie. University of Arizona. Laboratory of Tree-Ring Research; Estados Unidos Fil: Turney, Chris S.M.. University of New South Wales. Climate Change Research Centre; Australia Fil: Umer, Mohammed. Addis Ababa University. School of Earth Sciences; Etiopía Fil: van Ommen, Tas. Australian Antarctic Division; Australia. University of Tasmania. Antarctic Climate & Ecosystems Cooperative Research Centre; Australia Fil: Verschuren, Dirk. Ghent University. Department of Biology; Bélgica Fil: Viau, Andre E.. University of Ottawa. Department of Geography; Canadá Fil: Villalba, Ricardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Científico Tecnológico Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentina Fil: Vinther, Bo M.. University of Copenhagen. Niels Bohr Institute; Dinamarca Fil: von Gunten, Lucien . Past Global Changes (PAGES). International Project Office, ; Suiza Fil: Wagner, Sebastian. Helmholtz-Zentrum Geesthacht. Institute for Coastal Research; Alemania Fil: Wahl, Eugene R.. National Oceanic and Atmospheric Administration. National Climatic Data Center; Estados Unidos Fil: Wanner, Heinz. University of Bern. Oeschger Centre for Climate Change Research & Institute of Geography; Suiza Fil: Werner, Johannes P.. Justus Liebig University. Department of Geography, Climatology, Climate Dynamics and Climate Change; Alemania Fil: White, James W.C.. University of Colorado. Institute of Arctic and Alpine Research; Estados Unidos Fil: Yasue, Koh. Shinshu University. Department of Forest Science; Japón Fil: Zorita, Eduardo. Helmholtz-Zentrum Geesthacht. Institute for Coastal Research; Alemania

The radial variation of specific gravity and growth ring structures was studied in juvenile and mature wood of Tectona grandis L. grown naturally in dry (Chandrapur) and moist (Thane) deciduous forests of Maharashtra, India. Five trees each from age group of 48–66-year from Chandrapur and 120–154-year-old trees from Thane were selected. The study revealed that the mean specific gravity of growth rings in juvenile wood was more than the mature wood from both the sites. The annual growth in juvenile and mature period was higher in dry site than moist site. Ring width of juvenile and mature wood was 4.45 and 2.30 mm with the latewood content of 85.70 and 72.97%, respectively, in dry site. The patterns of radial variation of ring width, latewood content and specific gravity demonstrated inconsistency in juvenile to mature wood in both the sites. The specific gravity of all the five trees from both sites showed a poor association between ring width and latewood content in juvenile wood; however, it was positive and strong in most of the samples from mature wood. Considering mean values, there was a positive strong association between ring width and specific gravity in both juvenile and mature wood of both the sites. However, the latewood content did not show strong association with specific gravity. The overall result showed that ring width, specific gravity and latewood content vary among individuals within and between two sites. It is also important that individual tree variation needs to be studied while breeding for higher specific gravity rather than mean variation of all the trees in specific site.

Over the last few decades, weather and climate extremes have become a major focus of researchers, the media and general public due to their damaging effects on human society and infrastructure. Trends in indices of climate extremes are studied for the South Asian region using high-quality records of daily temperature and precipitation observations. Data records from 210 (265) temperature (precipitation) observation stations are analysed over the period 1971-2000 (1961-2000). Spatial maps of station trends, time series of regional averages and frequency distribution analysis form the basis of this study. Due to the highly diverse geography of the South Asian region, the results are also described for some specific regions, such as the island of Sri Lanka; the tropical region (excluding Sri Lanka); the Greater Himalayas above 35°N, the Eastern Himalayas (Nepal) and the Thar Desert. Generally, changes in the frequency of temperature extremes over South Asia are what one would expect in a warming world; warm extremes have become more common and cold extremes less common. The warming influence is greater in the Eastern Himalayas compared with that in the Greater Himalayas. The Thar Desert also shows enhanced warming, but increases are mostly less than in the Eastern Himalayas. Changes in the indices of extreme precipitation are more mixed than those of temperature, with spatially coherent changes evident only at relatively small scales. Nevertheless, most extreme precipitation indices show increases in the South Asia average, consistent with globally averaged results. The indices trends are further studied in the context of Atmospheric Brown Clouds (ABCs) over the region. Countries falling within the ABC hotspot namely Indo-Gangetic Plain (IGP) have shown a different behaviour on the trends of extreme indices compared with the parts outside this hotspot. IGP has increased temperature and decreased rainfall and tally closely with the actual trends.

Multi species tree-ring chronologies of the western Himalaya revealed strong significant negative relationship with potential evapotranspiration (PET) and vapor pressure (VP), and positive with moisture index (MI) and Palmer Drought Severity Index (PDSI) during spring season (March to May). The preliminary study showed that the MI and PDSI particularly in spring season might have a large scale positive association in developing of annual ring-width patterns, whereas PET and VP during the season are found not to be conducive for the trees growth. PET and VP from the beginning of the year 1917 showed strong influence on tree growth. High and low PET/VP might be associated with low and high MI/PDSI of the region. Extremely narrow ring width indices were observed in the year of 1921, 1941, 1953, 1954 and 1985 at most of the tree sites which are under the severe moisture stress condition due to extremely high PET and VP of the region. Also, extremely low PET and VP were found during 1917, 1933 and 1982, reflecting ring-width index above the normal due to enough moisture supply. Thus, the released and suppressed tree growth over the region is probably linked with the high and low MI/PDSI of the region. Loss or accumulation of soil moisture of the region might be precondition before the starting of growing season of the trees. The recent observation also suggests a weakening of VP and PET's influence on tree growth during recent few decades as compared to early period in sliding 31-years windows over western Himalaya. Correlation analysis of PET with MI and VP as well as PDSI for the period 1902–2002 during spring season indicated statistically strong correlation ( r = −0.53, 0.82, −0.50) respectively which is highly significant at 0.01% level.

South Asia covers more than 30° of latitude with weather observation stations situated from 6°N at Galle, Sri Lanka, to 36°N at Chitral in Pakistan. Moreover, the South Asian station network ranges in altitude from sea level to nearly 4000 m above sea level. This paper uses time series of 11 objectively defined indices of daily temperature extremes at 197 stations in Bangladesh, India, Nepal, Pakistan and Sri Lanka to examine the possible impacts of elevation and latitude on changes in temperature extremes over the period of 1971-2000. Trends in extreme indices are consistent with general warming only at low altitudes and latitudes. Stations at high altitudes and latitudes show both positive and negative trends in extreme temperature indices. As a notable example, the Diurnal Temperature Range (DTR), which has been known to decrease in most parts of the globe, has increasing trends over many high altitude stations in South Asia. Trends in extreme temperature indices at stations in South Asia higher than 2000 m above sea level are mostly in disagreement with those reported over the Tibetan Plateau. Observed trends at low altitude locations in South Asia suggest that these sites can generally expect future changes in temperature extremes that are consistent with broad-scale warming. High-elevation sites appear to be more influenced by local factors and, hence, future changes in temperature extremes may be less predictable for these locations.

Dendroclimatic research activities over the western Himalaya as well as central and peninsular India have been discussed. Wide network of conifers (Pinus, Abies, Picea, Cedrus) from western Himalaya indicates high dendroclimatic potential to reconstruct summer and winter temperature and rainfall for a millennium period. 553-year long tree-ring records over high altitude regions of western Himalaya give the history of warm and cold episodes. Anomalous higher growth during the recent few decades observed in these tree-ring records can partially be attributed to the overall warming trend over the region. Tree-ring variations in teak (Tectona grandis) from central and peninsular India is strongly influenced by monsoon rainfall and related global parameters (e.g. ENSO). They also show the strong positive relationship with moisture index at root zone and give the monsoon drought history of more than 500 years.

We developed a ring-width chronology of teak (Tectona grandis L.) from a moisture stressed area in Maharashtra, India. Bootstrapped correlation analysis indicated that moisture index (MI) and Palmer Drought Severity Index (PDSI) showed better performance rather than same year rainfall over the region. Tree-ring variations were most correlated positively with PDSI during different seasons compared with MI. Significant strong positive correlation with MI, and negative association with temperature and potential evapotranspiration (PET) were found during previous and current year post-monsoon (ON). This study shows that the moisture availability during the post-monsoon of the previous year has a significant role in the development of annual growth rings. The reconstructed previous year post-monsoon (−ON) moisture index for the period 1866–1996 indicates 3.5 and 29.3 years periodicities.

An unprecedented enhancement in growth during the last few decades is detected in the five tree-ring width chronologies of Himalayan conifers (Cedrus deodara D. Don; Picea smithiana Boiss) from the high altitude areas of the Kinnor and Gangotri regions, Western Himalaya. These chronologies indicate a strong positive relationship to the mean annual and winter (December–February) temperatures of the concurrent year. A 553-year-long master chronology prepared from the five individual chronologies shows few decadal and longer epochs of Little Ice Age (LIA) cooling during A.D. 1453–1590 and A.D. 1780–1930. Many of these events have been observed to be well related to the other proxy records of glacial fluctuations of the region. Analysis of instrumental period surface air temperature data over the region indicates significant increasing trend during the last century with a noticeable enhanced warming in the recent four decades. The time series of annual highest values of daily maximum and minimum temperatures also show increasing trend. Direct significant relationship of winter temperature to the tree growth is mainly because of moisture availability for a longer period due to higher degree of snow melt in winter and early spring. Therefore, accelerated tree-ring growth during the last few decades can partially be attributed to the overall warming trend over the region.

Results of interannual variations in cellulose oxygen isotopic composition (δ18O) of four teak (Tectona grandis L.F.) trees (one from western India, two from central India and one from southern India) are presented. Cellulose δ18O of teak trees from western and central India show a significant positive correlation with the amount of rainfall, which is contrary to expectation. We propose that this correlation is caused by longer duration of the growing season in years of higher rainfall. Teak from southern India shows a significant negative correlation with the amount of rainfall and this relationship is used to reconstruct rainfall back to A.D. 1743, extending the existing regional and local rainfall records by 70 and 128 years, respectively. The reconstructed series reveals higher rainfall for the period 1743–1830 than for the later periods.

We present a 523-year (A.D. 1481–2003) tree-ring width index chronology of Teak ( Tectona grandis L.F.) from Kerala, Southern India, prepared from three forest sites. Dendroclimatological investigations indicate a significant positive relationship between the tree-ring index series and Indian summer monsoon rainfall (ISMR) and related global parameters like the Southern Oscillation Index (SOI). A higher frequency of occurrence of low tree growth is observed in years of deficient Indian monsoon rainfall (droughts) associated with El Nino since the late 18th century. Prior to that time, many low tree growth years are detected during known El Nino events, probably related to deficient Indian monsoon rainfall. The general relationship between ISMR and El Nino is known to be negative and the spatial correlations between our Kerala tree-ring chronology and sea surface temperatures (SSTs) over the Nino regions follow similar patterns as those for ISMR. This relationship indicates strong ENSO-related monsoon signals in the tree-ring records. These tree-ring chronologies with a high degree of sensitivity to monsoon climate are useful tools to understand the vagaries of monsoon rainfall prior to the period of recorded data.

Ring-width chronologies (AD 1919–2000, 1827–2000 and 1857–2001) of teak ( Tectona grandis ) from three different tree sites in Central India were developed. The site chronologies show the influence of a common forcing factor, which could be climate, largely the moisture index. Correlation between April–September moisture index with tree-ring chronologies shows a significant positive relationship for the period 1901–2000. Regional tree-ring chronologies revealed a strong association with moisture index since the late 20th century. Multi-decadal variation in tree-ring chronologies exhibits a similar pattern to those of chronologies of adjacent areas, suggesting that summer (April–September) moisture index might be one of the parameters limiting the growth of teak trees over a large spatial scale.

A 458-year-long regional tree-ring-width index chronology of Himalayan cedar (Cedrus deodara D. Don) prepared from three high-elevation sites of Western Himalaya has been presented. Dendroclimatological investigation indicates significant positive relationship of tree-ring index series with winter (December–February) temperature and summer precipitation and inverse relationship with summer temperature. Higher growth in the recent few decades detected in the tree-ring chronology has been noticed coinciding with the rapid retreat of the Himalayan glaciers. Suppressed and released growth patterns in tree-ring chronology have also been observed to be well related to the past glacial fluctuation records of the region. The higher tree growth in recent decades may be partially attributed to the warming trend over the region, particularly increasing the winter warmth, and thus to the regional manifestations of global warming.

Tree-ring-width index chronologies of teak (Tectona grandis L.F.) from three sites in central India have been studied for their dendroclimatic potential. The existence of good correlation among the three site chronologies indicates the influence of common forcing factor to the tree growth of the region. Tree growth and climate relationship based on correlation analysis revealed the important contribution of moisture index and rainfall rather than the direct influence of the temperature on tree growth during different seasons. Significant positive relationship of moisture index and rainfall during the monsoon months as well as on the annual scale with tree-ring width variations over the region indicates the important role of moisture availability at the root zone. The results suggest that the teak tree-ring chronologies can be used as high resolution proxy for past precipitation and moisture level in the environment.

The present study examines the long term trend in sea surface temperatures (SSTs) of the Arabian Sea, Bay of Bengal and Equatorial South India Ocean in the context of global warming for the period 1901–2002 and for a subset period 1971–2002. An attempt has also been made to identify the relationship between SST variations over three different ocean areas, and All-India and homogeneous region summer monsoon rainfall variability, including the role of El-Nino/Southern Oscillation (ENSO). Annual sea surface temperatures of the Arabian Sea, Bay of Bengal and Equatorial South India Ocean show a significant warming trend of 0.7 °C, 0.6 °C and 0.5 °C per hundred years, respectively, and a relatively accelerated warming of 0.16 °C, 0.14 °C and 0.14 °C per decade during the 1971–2002 period.

Statistical Models of Climate Reconstruction using Tree Ring Data

In the present study, a regional tree-ring chronology prepared from two species ( Picea smithiana and Cedrus deodara ) over the western Himalaya has been used in relation to climate fluctuations. This analysis shows that moisture index and rainfall during February to May have significant positive relationship, whereas temperature and heat index show a negative relationship with tree growth. However, moisture and heat indices show greater impact on tree growth than rainfall and temperature. The strong association of tree-ring chronology with moisture demonstrates that tree rings are much more sensitive to the availability of moisture at the root zone, which enabled us to extend our analysis back to AD 1789; in the present reconstruction, moisture deficiency for two consecutive years was noticed during 1846-1847, 1908-1909, 1921-1922, 1931-1932, 1947-1948 and 1966-1967.

Studies on climate variability over the region of monsoon Asia mostly during the Quaternary, based on various sources of proxy data have been reviewed. Increasing interest to understand the processes of monsoon system over the Asian region as well as the availability of data from variety of reliable proxy sources such as, ocean sediments, ice cores and historical documents have encouraged the palaeoclimatic studies in this region. Inferences drawn from the multiproxy sources indicate good association of glacial and inter-glacial phases with over all monsoon flow. Warm and wet periods are generally characterized by strong summer monsoon, where as, weak monsoonal activities were observed during cold and dry periods. All India monsoon rainfall since early 17th century based on dendroclimatic reconstructions shows trend-less nature with large interannual variability as seen in the instrumental record of recent century. Historical evidences over this region are a potential source of information on contemporary climate change.

Cores of Cedrus deodara D. Don from two different sites of western Himalaya were subjected to densitometric analysis to obtain data for earlywood, latewood, minimum, maximum, and mean densities and total ring width. Most of these variables show moderately high values of common variance and signal to noise ratio except latewood and maximum densities. These analyses suggest density parameters of this species may be useful in dendro climatic studies. Response function analyses indicate significant relationships between pre-monsoon (March-April-May) summer climate and earlywood density parameters, as well as total ring width. Based on the relationships derived from response function analyses, the potential of tree-ring chronologies from this species to provide reconstructions of the pre-monsoon climate in western Himalayan region has been established.

Global climate change has multidimensional impacts with several biological fingerprints, and treeline shifting in tandem with climate change is a widely observed phenomenon in various parts of the world. In Nepal several impacts of climate change on physical environments have been observed. However, studies on the biological impacts are lacking. This dendrochronological study was carried out at the treeline ecotone (3750–4003 m a.s.l.) in the Kalchuman Lake (Kal Tal) area of the Manaslu Conservation Area in central Nepal Himalaya with the aim to study the dynamic impact of climate change at the treeline. The study provides an insight into regeneration and treeline dynamics over the past 200 yr. Two belt transect plots (size: 20 m wide, >250 m long) were laid covering forest line, treeline as well as tree species Abies spectabilis and Betula utilis was done and their tree-cores were collected. Stand character and age distribution revealed an occurrence of more matured B. utilis (max. age 198 yr old) compared to A. spectabilis (max. age 160 yr). A. spectabilis contained an overwhelmingly high population (89%) of younger plants (

Tree-ring anlaysis of Cedrus deodara from three different sites of western Himalaya has been carried out. The chronologies include 47 cores (26 trees) from Manali, 33 cores (18 trees) from Kufri (Shimla) and 25 cores (13 trees) from Kanasar forest sites. Moderately high values of common variance exhibited by all three chronologies indicate the great potential of the species for dendroclimatic studies. Response function and correlation analyses using the above tree-ring-width data and Shimla climate show a significant negative relationship with summer temperature and positive relationship with summer precipitation. Based on these results, calibration equations have been developed for different periods, and appropriately verified using independent data, to reconstruct the summer (March–April–May) temperature at Shimla. The reconstruction has extended the temperature record of the region back to the eighteenth century.

The extensive coniferous forests of the western Himalayas provide great potential for dendroclimatic research. Abies, Cedrus, Picea and Pinus are the main tree genera of the region, consisting of many old and living trees. The annual growth-ring patterns of these trees, which can be precisely dated, contain valuable high-resolution information on climate variability over the past few centuries. This paper presents an analysis of the ring-width data of Abies pindrow and Picea smithiana based on samples collected from forest sites around Pahalgam in the Kashmir Valley in 1982. The non- climatic variations have been filtered out of the raw ring-width series using a cubic spline smoothing, and ring-width index series have been obtained. The mean ring-width index chronologies have been prepared by averaging the indices of 13 samples for P. smithiana and eight samples for A. pindrow. The maximum lengths of mean ring-width index chronologies are 208 years (1775-1982) for P. smithiana and 371 years (1612-1982) for A. pindrow. Response functions have been developed using the instrumental record of monthly mean temperature and rainfall at Srinagar during the period 1893-1982. Both ring- width chronologies indicate a significant negative response to summer temperature and a significant positive relationship with summer precipitation. Calibration and verification analysis has been carried out for different combinations of months using a multiple species ring-series network and the summer precipitation at Srinagar has been reconstructed back to the eighteenth century.

[1] Intra-annual variations in the cellulose oxygen isotopic composition (δ18O) of several annual growth rings of three teak (Tectona grandis L.F.) trees from central India show a clear seasonal cycle with higher values in the early and late growing seasons and lower values in the middle. This cycle is useful to identify growth occurring during different phases of the growing season. Relative humidity (RH) appears to control the intra-annual δ18O variations rather than rainfall, and therefore past break-monsoon conditions associated with lower RH, could be detected by high resolution sub-sampling of annual rings for δ18O analysis.

The climate of a place represents the average weather in that place over more than thirty years’ time period. While the weather can change in just a few hours, climate changes over longer time frames. Climate change is the variation in the Earth’s global climate or in regional climates over time. It involves the variability or average state of the atmosphere over durations ranging from decades to millions of years. These changes can be caused by dynamic processes on the earth, external forces and human activities. Detection of change in climate against its variability is a key issue in climate research. Climate change is often expressed simply in terms of changes in the mean climate. However, regional climatic change in terms of extremes could have more significant socio-economic consequences than the changes in mean climate conditions as they may not show an appreciable change but may be characterized by a variety of extreme situations. There is a general agreement within the climate community that changes in the frequency as well as the intensity of extreme climate events would have profound impacts on natural and social systems. They can have serious and detrimental effects on human society and infrastructure as well as on ecosystems and wildlife. In general, the relationship between climate, extreme events and the extent of damage is extremely complex. The extreme events such as heat waves, floods, storms and dangerous avalanches have caused repeated concern in recent years. Our present knowledge of meteorological processes suggests that frequency and intensity of certain extreme events— for example, number of hot days and nights, heat waves, heavy precipitation and flood situations—will increase with the change in climate. However it remains uncertain whether or not to expect changes in some other extremes. The information based on current meteorological processes and model simulations must be taken into account in risk assessment, planning of precautionary measures and in development processes.

The long-term variability of the Indian summer monsoon rain-fall and related regional and global parameters are studied. The cubic spline is used as a digital filter to smooth the high frequency signals in the time series of the various parameters. The length of the data series varies from 95 to 115 years during the period 1871-1985. The parameters studied within the monsoon system are: (a) monsoon rainfall of the country as a whole; (b) number of break-monsoon days during July and August; (c) number of storms/ depressions in Bay of Bengal and Arabian Sea during summer monsoon season; and (d) dates of onset of summer monsoon over South Kerala Coast. The parameters studied outside the monsoon system are: (a) the Wright’s Southern Oscillation Index (June-July-August); (b) the January mean Northern Hemispheric surface air temperature anomaly; and (c) the East-equatorial Pacific sea surface temperature anomaly.