Analysis of Climate Variability in a Part of Brahmaputra River Basin in India
01 Jan 2017-pp 113-142
TL;DR: In this paper, an attempt has been made to detect the trends in rainfall and temperature (past and future) time series and the possibility of any rational relationship between the trends and elevation over study region.
Abstract: Regional specific study of the most important climatic variables is essential to reduce the adverse effects of climate change in developing countries. In the present study, an attempt has been made to detect the trends in rainfall and temperature (past and future) time series and the possibility of any rational relationship between the trends and elevation over study region. The study was mainly focused on a part of Brahmaputra river basin in Northeast India, i.e., the Dikhow catchment (area = 3100 km2). The Dikhow catchment is a set of unique composite catchment topography comprising fairly higher altitude hills as well as alluvial plains at much lower elevation. Historically (from the year 1901 to 2002), annual precipitation and monsoon precipitation are decreasing significantly (5 % level of significance), whereas significant rise was observed on annual and seasonal basis for both maximum and minimum temperature time series. Further, during the entire time series (1901–2002), significant negative correlation was obtained between precipitation (annual and monsoon) trend magnitude and elevation of the study region. Significant rise for future precipitation was identified over the region for both A2 and B2 SRES scenarios, and winter precipitation is likely to increase more (59.18–69.44 % under A2 and 47.71–54.90 % under B2 over the catchment) than summer and monsoon precipitation. The maximum temperature has higher rate of rise than the minimum temperature for annual, summer, and monsoon temperature time series, while winter season shows higher rate of rise rather than the maximum temperature (1.02 °C over 102 years). For diurnal temperature range (DTR), monsoon season shows the significant rising which varies from 0.0016 to 0.0021 °C/year. Extreme temperature indices (TXx, TXn, TNx, and TNn) also show the significant warming picture over the catchment. Trend magnitude of extreme temperature indices and elevation shows significant relationship, while trend magnitude of the average maximum and minimum temperature and DTR does not show the noticeable connection between warming rate and elevation of the study area. Future Tmax and Tmin are increasing sharply for both A2 and B2 scenarios. A2 scenario shows higher rate than the B2 scenario.
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TL;DR: In this article, the authors detected the long term annual and seasonal rainfall trends over Bihar state, India, between 1901 and 2002, and identified the shift change point with the cumulative deviation test (cumulative sum) and linear regression.
Abstract: This study detected, for the first time, the long term annual and seasonal rainfall trends over Bihar state, India, between 1901 and 2002. The shift change point was identified with the cumulative deviation test (cumulative sum – CUSUM), and linear regression. After the shift change point was detected, the time series was subdivided into two groups: before and after the change point. Arc-Map 10.3 was used to evaluate the spatial distribution of the trends. It was found that annual and monsoon rainfall trends decreased significantly; no significant trends were observed in pre-monsoon, monsoon, post-monsoon and winter rainfall. The average decline in rainfall rate was –2.17 mm·year⁻¹ and –2.13 mm·year⁻¹ for the annual and monsoon periods. The probable change point was 1956. The number of negative extreme events were higher in the later period (1957–2002) than the earlier period (1901–1956).
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TL;DR: In a warmer world, less winter precipitation falls as snow and the melting of winter snow occurs earlier in spring, which leads to a shift in peak river runoff to winter and early spring, away from summer and autumn when demand is highest.
Abstract: All currently available climate models predict a near-surface warming trend under the influence of rising levels of greenhouse gases in the atmosphere. In addition to the direct effects on climate--for example, on the frequency of heatwaves--this increase in surface temperatures has important consequences for the hydrological cycle, particularly in regions where water supply is currently dominated by melting snow or ice. In a warmer world, less winter precipitation falls as snow and the melting of winter snow occurs earlier in spring. Even without any changes in precipitation intensity, both of these effects lead to a shift in peak river runoff to winter and early spring, away from summer and autumn when demand is highest. Where storage capacities are not sufficient, much of the winter runoff will immediately be lost to the oceans. With more than one-sixth of the Earth's population relying on glaciers and seasonal snow packs for their water supply, the consequences of these hydrological changes for future water availability--predicted with high confidence and already diagnosed in some regions--are likely to be severe.
3,831 citations
TL;DR: In this article, an analysis of the global mean surface air temperature has shown that its increase is due, at least in part, to differential changes in daily maximum and minimum temperatures, resulting in a narrowing of the diurnal temperature range.
Abstract: Analysis of the global mean surface air temperature has shown that its increase is due, at least in part, to differential changes in daily maximum and minimum temperatures, resulting in a narrowing of the diurnal temperature range (DTR). The analysis, using station metadata and improved areal coverage for much of the Southern Hemisphere landmass, indicates that the DTR is continuing to decrease in most parts of the world, that urban effects on globally and hemispherically averaged time series are negligible, and that circulation variations in parts of the Northern Hemisphere appear to be related to the DTR. Atmospheric aerosol loading in the Southern Hemisphere is much less than that in the Northern Hemisphere, suggesting that there are likely a number of factors, such as increases in cloudiness, contributing to the decreases in DTR.
1,459 citations
01 Nov 1997
TL;DR: In this paper, an analysis of changes in the diurnal temperature range (DTR) for many parts of the globe is presented, which includes data for an additional 15% of the global land area and an extension of the analysis period used in previous studies.
Abstract: A number of recent studies have established that differential changes in daily maximum and minimum temperatures are occurring, resulting in changes in the diurnal temperature range (DTR) for many parts of the globe. Large-scale trends in the USA indicate that minimum temperatures are increasing at a faster rate than maximum temperatures, resulting in a narrowing in the DTR. This paper updates and extends the analysis of changes in the DTR in three ways: (1) by increasing the areal coverage to more than half the global landmass, (2) by addressing the issue of homogeneity of the data, and (3) by examining the potential effects of urban stations on the calculated trends. The update includes data for an additional 15% of the global land area and an extension of the analysis period used in a previous study. Homogeneity techniques were used on the data to adjust individual station data for undocumented discontinuities. Annual maximum and minimum temperature and DTR time series for the 1950-1993 period averaged over 54% of the total global land area are presented. The trend for the maximum temperature is 0.88 C/100 years, which is consistent with earlier findings. However, the trend for the minimum temperature is 1.86 C/100more » years; this is less than found in previous analyses and leads to a smaller trend in the DTR. This finding is not surprising since much of the data added in this study are for tropical and sub-tropical regions where temperature trends are not expected to be as large as in higher latitude regions. The effect of urbanization on the global trends is found to be on the order of 0.1 C/100 years or less, which is consistent with previous investigations. 14 refs., 2 figs.« less
1,392 citations
TL;DR: In this paper, a statistical downscaling technique, in which local values are inferred from observed atmospheric predictor variables, is compared against two dynamical down-scaling techniques, based on the use of the screen temperature or precipitation simulated at the nearest grid point in integrations of two climate models.
Abstract: An assessment is made of downscaling estimates of screen temperature and precipitation observed at 976 European stations during 1983–94. A statistical downscaling technique, in which local values are inferred from observed atmospheric predictor variables, is compared against two dynamical downscaling techniques, based on the use of the screen temperature or precipitation simulated at the nearest grid point in integrations of two climate models. In one integration a global general circulation model (GCM) is constrained to reproduce the observed atmospheric circulation over the period of interest, while the second involves a high-resolution regional climate model (RCM) nested inside the GCM. The dynamical and statistical methods are compared in terms of the correlation between the estimated and observed time series of monthly anomalies. For estimates of temperature a high degree of skill is found, especially over western, central, and northern Europe; for precipitation skill is lower (average corre...
524 citations
TL;DR: In this paper, the authors identify regional patterns in both δ18O and deuterium excess (D excess), defined as δD − 8δ 18O, and in particular the northward maximum extent of the southwest monsoon over the Tibetan Plateau.
Abstract: [1] In this study, individual precipitation samples, collected over 2 years at stations in different climatic regions of west China (Tibetan Plateau region, Tianshan region, and Altay) were analyzed for the stable isotopes of precipitation to improve our understanding of how vapor transport impacts the modern stable isotopic distribution. Our results identify regional patterns in both δ18O and deuterium excess (D excess, defined as δD – 8δ18O), and in particular we have identified the northward maximum extent of the southwest monsoon over the Tibetan Plateau. This demarcation is also the boundary for the fractionation effect of temperature on stable isotopes in precipitation. The patterns we have identified are as follows: (1) In the southern Tibetan Plateau, along the southern slope of the Himalayas, our results show a distinct seasonality for both δ18O and D excess as a result of the shift of summer monsoon moisture and winter westerly moisture transport. The signals of δ18O in the western Tibetan Plateau reveal that the region receives southwest monsoonal moisture. In the east of the plateau, stable isotopic variation shows alternation between monsoon intrusion and recycling of northern moisture. (2) In contrast, in Tianshan there is an apparent “temperature effect” in δ18O, with enriched values occurring in summer and depleted values occurring in winter. Seasonal D excess values, opposite to those observed in the southern Tibetan Plateau, are controlled by differing seasonal evaporation conditions. (3) In Altay, the most northern mountain region, the seasonal δ18O shows the same variation with that in Tianshan region. However, D excess shows no apparent seasonal variation.
477 citations