Browsing by Author "Ramesh Kumar Yadav"

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Reconstruction of potential evapotranspiration over western Himalaya in India based on tree ring-width records
(Elsevier Ltd, 2020) Somaru Ram; H.N. Singh; Ramesh Kumar Yadav; S.S. Nandargi; Manoj K. Srivastava
Tree-ring chronologies from different sites of western Himalaya have been used in this study to examine the climate variability/change over the region. The 1st principal component (PC1) which has been computed by multi species tree ring chronologies of western Himalaya is negatively correlated with heat index (HT), temperature (TM) and potential evapotranspiration (PET) but positively with the rainfall of the region during spring season. However, HT and PET showed the stronger influence on tree growth than temperature which has been used to reconstruct the spring season PET back to A.D. 1779. The extended periods of low PET have been found at ending phase of Little Ice Age (LIA) during 1827–1845. The reconstructed PET showed that the advance of the glaciers over the western Himalaya might have influence on reduction of downward shortwave radiation on the earth's surface; which may in turn cause low temperature and low PET over the region. The result indicates that longer tree ring chronologies from the western Himalaya are very useful to get valuable information on PET and glacier fluctuation during the last few centuries. The highest PET in the entire reconstruction was noticed during the year 1921 in the 20th century, which has been associated with lowest trees growth in the entire western Himalaya. © 2019 Elsevier Ltd and INQUA
Standardized Precipitation Index reconstruction during the last two centuries over western Himalaya, India: deduced by tree ring-width records
(Wadia Institute of Himalayan Geology, 2020) Somaru Ram; Ramesh Kumar Yadav; H.N. Singh; Manoj K. Srivastava
Tree-ring width index chronologies of three different species (Cedrus deodara, Abies pindrow and Picea smithiana) from the western Himalaya have been carried out in relation to understand the climate fluctuations. The first principal component developed based on the above species showed significant positive relationship with Standardized Precipitation Index (SPI) and negative with Heat Index (HI) during pre-monsoon month, but the highest correlation coefficients of tree growth with heat and SPI were observed during May, are-0.52 and 0.60 respectively, which are highly significant at 0.1% level. The results indicate that increasing heat index during May might lead to dry soil by accelerating the potential evapotranspiration which creates the moisture deficiency over the region. The significant positive relationship of tree growth with SPI indicates that tree growth of the western Himalaya is moisture sensitive, which enable us to extend SPI to monitor dry and wet periods before the instrumental period. The reconstructed SPI back to 1778 shows climate variability, on both inter-annual and inter-decadal time scale. The reconstruction showed increasing wetness in the twentieth century and recent few decades. Extreme and severe dry is noticed during 1921 (-2.4) and 1892 (-2.0) in the entire reconstruction has been associated with very low tree growth during the corresponding year over the western Himalaya. © 2020, Wadia Institute of Himalayan Geology. All rights reserved.
Tree rings-width study of western Himalaya and its linkage with boreal spring vapor pressure and wet-day frequency
(Springer, 2019) Somaru Ram; H.N. Singh; Ramesh Kumar Yadav; Manoj K. Srivastava
Tree ring chronologies from different sites of hill forest in the western Himalaya of India have been carried out in relation to natural climate variability/change. The first principal component (PC1) prepared by using a multiple site tree ring-width chronologies of the western Himalaya is strongly negatively correlated with vapor pressure and positively with wet-day frequency. The correlation coefficients of PC1 with boreal spring season vapor pressure and wet-day frequency are − 0.61 and 0.42, respectively, indicating significant level at 0.1%. The relationship indicated that wet-day frequency and vapor pressure of the western Himalaya have significant role in modulating tree growth patterns during boreal spring season (March to May). The results indicate that increasing vapor pressure during boreal spring season may cause high transpiration and evaporation, which results in moisture stress condition over the region and has adverse impact on trees growth. © 2019, Indian Academy of Wood Science.
Variations in vapor pressure and standardized precipitation evapotranspiration index since AD 1861 over the western Himalaya in India: inference from tree ring-width records
(Springer, 2020) Somaru Ram; H.N. Singh; Ramesh Kumar Yadav; Hamza Varikoden; S.S. Nandargi; Manoj K. Srivastava
A regional tree ring-width index chronology prepared from various tree core samples of the western Himalaya has been analyzed in relation to climate fluctuations. The correlation analysis of tree ring chronology shows significant positive correlations with regional rainfall and standardized precipitation evapotranspiration index (SPEI) and negative correlations with temperature and vapor pressure (VP) during the spring season. The correlation coefficients (CCs) of tree ring-width index chronology with rainfall, temperature, SPEI, and VP during 1901–1990 are 0.50, −0.49, 0.65, and −0.51, respectively. All CCs are significant at 0.1% level. The highly significant CCs between tree ring-width index chronology and SPEI indicate that tree growth over the western Himalaya is more sensitive to soil moisture availability than rainfall, whereas the rising VP is found to have a significant moisture stress condition to tree growth by accelerating the evapotranspiration, which is not conducive for the development of tree growth in the region. So, based on the strong association between tree ring-width index chronology and SPEI; the reconstructions of SPEI and VP are developed back to AD 1861, that show the long period of dryness during 1936–1963. © 2020, Springer-Verlag GmbH Austria, part of Springer Nature.