Amalava Bhattacharyya

Spring-temperature variations in western Himalaya, India, as reconstructed from tree-rings: AD 1390-1987

The Himalayan region plays a very important role in influencing the regional and extra-regional circulation system. Long-term instrumental or proxy climate records for this region are scant, but are essential for a global perspective of climate variability. A 598-year (AD 1390-1987) reconstruction of spring (March-May) temperature has been derived for the first time for the western Himalayan region, India using a well replicated ring-width chronology of Himalayan cedar (Cedrus deodara (D. Don) G. Don). The reconstruction showing annual to multi-year episodes of cool and warm springs is well correlated with the instrumental record of spring temperature for 1876-1987 (r = 0.53, p < 0.001). Prominent large-magnitude century-scale excursions in negative anomalies of spring temperature which might reflect the regional influence of the ‘Little Ice Age’ are not indicated in our data. The seventeenth century experienced monotonically warm springs. Neither recostruction or instrumental data provide evidence of warming during the last few decades of this century which could be attributed to anthropogenic causes. A strong out-of-phase relationship between the instrumental sprin-temperature record over the western Himalayan region and sea-surface temperatures (SSTs) of ensuing months (June-May) over the equatorial Pacific Ocean has been noted. This suggests that temperature responsive tree-ring chronologies from the Himalayan region could also serve as a valuable proxy of the Southern Oscillation.

Late-Summer Temperature Reconstruction of the Eastern Himalayan Region Based on Tree-Ring Data of Abies densa

Abstract Tree-ring analysis from Abies densa growing at the treeline in the Eastern Himalayan region reveals that temperature during late summer (July–September) plays a significant role in controlling the growth of this tree. Mean temperature of each year for these three months has been reconstructed based on this ring-width data. This record goes back to A.D. 1507; however data prior to A.D. 1757 are questionable because they are based on only one sample. The reconstructed temperature series for the last 237 yr shows annual to multiyear fluctuations punctuated with cool and warm periods. The warmest and coolest 10-yr periods of the entire span occurred in 1978–1987 (+0.25°C) and 1801–1810 (−0.31°C), respectively.

Tree-ring studies in India past appraisal, present status and future prospects.

A large number of tree species, especially of conifers growing in the Himalaya and a few broad-leaved taxa in the peninsular region, have been dendrochronologically analyzed in India. This paper is a review providing information as regards the present status and future prospects of tree-ring research in India. Many trees are recorded to have datable tree rings but only some of them have been used for climate reconstruction and other aspects, e.g., glacial fluctuation or palaeo-seismic dating. In future not only ring width which is widely used so far, but also other tree-ring parameters need to be analyzed for a better understanding of the regional climate and its linkage with other climatic phenomena in a global perspective.

Climatic Reconstructions Using Tree-Ring Data from Tropical and Temperate Regions of India - A Review

There are several reports which indicate that the c1imate over the Himalayan region is linked both with the monsoon variation on the Indian subcontinent and in the whole of South-East Asia as well as with the El-Nino/Southem Oscillation. To understand the behaviour ofthese c1imatic phenomena we need long-term high-resolution c1imatic records which are in generallacking in this part of the globe. Tree-ring studies have therefore been taken up in the tropical and Himalayan region in India to develop millennium-long c1imatic reconstructions.

Tree-Ring Studies in the Eastern Himalayan Region: Prospects and Problems

Tree-ring sampies of different conifer species in various ecological settings from subtropical to temperate regions of the Eastern Himalayan region have been evaluated for their potential for dendroc1imatic reconstructions. Most of these tree species have cross-datable growth rings except Taxus baccata and Tsuga dumosa where series of micro-rings and lack of variation in these suppressed zones make cross-dating difficult. Tree-ring chronologies have been established from Abies densa and Larix griffithiana, the only deciduous conifer species in the Himalayas. Tree growth-climate relationships reveal that temperature is a determinant factor for the growth of trees at high elevations. Abies densa in the western part of Arunachal Pradesh shows a negative response to the July-September temperature whereas Larix griffithiana shows a positive response to the May temperature.

Potential for Developing Fire Histories in Chir Pine (Pinus roxburghii) Forests in the Himalayan Foothills

Abstract We report on the potential for developing long-term fire histories from chir pine (Pinus roxburghii Sarg.) forests in the Western Himalayan foothills based on a preliminary study from a stand located in the state of Uttarakhand in northern India. Rings from trees collected to develop a master skeleton plot chronology were generally complacent with false rings present during most years, but were crossdatable with only minor difficulty. The oldest tree confidently crossdated back to 1886, with good sample depth (5 trees) from 1911, which helped date the fire scars in cross-sections collected from three trees. Fire frequency as determined from fire-scar dates was high, with mean and median fire intervals of 3 years from 1938 to 2006. Fires were likely from human ignitions given the prevalence of human land use in the site. Fire scars were generally recorded at false-ring boundaries and likely represent burning during the hot, dry period in May or early June before the onset of monsoon rainfall beginning in mid-June. Although only three fire-scarred trees were sampled, this preliminary assessment shows there is a potential for additional samples from other stands to develop longer-term fire histories to better understand the role of fire in the ecology and management of chir pine throughout its range in the Himalaya region.

Modern vegetational distribution and pollen dispersal study within Gangotri glacier valley, Garhwal Himalaya

Modern pollen-vegetation relationship has been analyzed in respect to vegetational distribution and pollen dispersal from sub-alpine and alpine ecological regimes within the higher reaches of the Gangotri glacier valley. The results in general cope with the local ecological conditions of the sites within the valley. Above the tree line limits, the pollen frequency of arboreal taxa is found lower than those of non-arboreal taxa. In contrast the pine-birch forest area at Chirbasa represented the frequency of arboreal pollen (AP) more than that of non-arboreal pollen (NAP) due to over representation of Pinus wallichiana (conifer). Pollen grains of extra-local arboreal elements, mostly conifers have also been recorded here with fair amount of temperate broad-leaved arboreal taxa viz. Quercus, Alnus, Corylus, Carpinus, Ulmus, Juglans etc. that have been transported by the upthermic winds from their growing limits at lower altitudes to the study sites at higher altitudes. Non-arboreal taxa viz. marshy/aquatic, steppe and of other herbaceaous taxa, represents the existing ecological regimes of their respective sites within the valley. Differential pollen preservation has been observed between the moss cushion and sediment samples from the same site that may be due to the direct exposure of moss cushions to air, thus showing more concentration of wind pollinated pollen-spores as compared to surface sediments.

Himalayan glaciers experienced significant mass loss during later phases of little ice age

To date, there is a gap in the data about the state and mass balance of glaciers in the climate-sensitive subtropical regions during the Little Ice Age (LIA). Here, based on an unprecedented tree-ring sampling coverage, we present the longest reconstructed mass balance record for the Western Himalayan glaciers, dating to 1615. Our results confirm that the later phase of LIA was substantially briefer and weaker in the Himalaya than in the Arctic and subarctic regions. Furthermore, analysis of the time-series of the mass-balance against other time-series shows clear evidence of the existence of (i) a significant glacial decay and a significantly weaker magnitude of glaciation during the latter half of the LIA; (ii) a weak regional mass balance dependence on either the El Niño-Southern Oscillation (ENSO) or the Total Solar Irradiance (TSI) taken in isolation, but a considerable combined influence of both of them during the LIA; and (iii) in addition to anthropogenic climate change, the strong effect from the increased yearly concurrence of extremely high TSI with El Niño over the past five decades, resulting in severe glacial mass loss. The generated mass balance time-series can serve as a source of reliable reconstructed data to the scientific community.