Long-Term (1951–2007) Rainfall Trends around Six Indian Cities: Current State, Meteorological, and Urban Dynamics
TL;DR: In this paper, the authors focused on analyzing the precipitation trends over six Indian cities during the summer monsoon (June-September) covering the period 1951-2007 and also attempted to investigate possible urban forcing and dynamics by examining the variation in precipitation in the upwind and downwind directions.
Abstract: The present study focuses on analyzing the precipitation trends over six Indian cities during the summer monsoon (June–September) covering the period 1951–2007 and also attempting to investigate possible urban forcing and dynamics by examining the variation in precipitation in the upwind and downwind directions. The analysis shows negative trends in the total number of rainy days over Hyderabad (−10.4%), Kanpur (−7.1%), Jaipur (−10.5%), and Nagpur (−4.8%) and positive trends over Delhi (7.4%) and Bangalore (22.9%). On the other hand, decreases of −21.3%, −5.9%, −14.2%, and −14.6% in seasonal rainfall are found over Delhi, Hyderabad, Jaipur, and Kanpur, respectively, whereas Bangalore and Nagpur show 65.8% and 13.5% increase. The lesser rainfall and rainy days, along with the mostly declining trend, in the downwind directions of the cities may imply an urban influence in precipitation associated with the increased anthropogenic emissions due to expansion of the urban areas and the increase of population. However, the large spatiotemporal variability of precipitation and the lack of statistical significance in the vast majority of the trends do not allow the extraction of safe conclusion concerning the aerosol-precipitation interactions around Indian cities.
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TL;DR: Wang et al. as discussed by the authors integrated the Chinese stalagmite oxygen isotope sequence to reconstruct the tropical Pacific sea surface temperature gradient, i.e., the large-scale ENSO-like state over the past millennium.
Abstract: The question of whether or not global warming has paused since more than ten years ago, namely “warming hiatus”, has attracted the attention of climate science community including the IPCC. Some authors have attributed the “warming hiatus” to the internal changes in the climate system, i.e., the recombination of ocean-atmosphere circulations. Therefore, it is necessary to propose higher requirements on reconstructing circulation background of climate change for the past millennium. However, the analyses of changes in atmospheric circulation over the last millennium as well as the conclusions of related regional climate patterns are so widely different and contradictory, bringing uncertainties to our understanding of regional even global climate change to a great extent. On the other hand, in the last 10 years the high-precision U/Th-dated stalagmite oxygen isotope ratio ( δ 18O) sequences provided an accurate chronological frame for the paleoclimate study of the middle and late Pleistocene, in which all authors from China took the Chinese stalagmite δ 18O as the summer monsoon index without exception. However, this point of view misleads the climate scientists into thinking that the stalagmite δ 18O can be as the proxy of precipitation amount. Nevertheless, it is well known that all of these records have a lot in common in the low frequency trend. However, most sequences cannot be calibrated by instrumental precipitation records, and thus the uncertainty of the climate research framework of China and even of the world has increased. Therefore, it is imperative for climatology to clarify the origin of contradiction and to reduce the uncertainty as early as possible. On the basis of analyzing the significance of stalagmite δ 18O in the monsoon regions of China, the author tries to propose a new circulation proxy in this paper: integrating the Chinese stalagmite oxygen isotope sequence to reconstruct the tropical Pacific sea surface temperature gradient, i.e., the large-scale ENSO-like state over the past millennium. Furthermore, the author speculates that it was warm in the modern times and the Medieval Period, but the circulation recombination was different in both periods. And this inference could be supported by the longer record since Last Glacial Maximum. In other words, the attribution analysis of the identical low-frequency trends of Chinese stalagmite δ 18O on a largescale shows that the ENSO-like state controls the climate change in the monsoon regions of China at different time scales (from interannual to century or even longer time scales). Wherein the important connection of circulations is the western Pacific subtropical high (WPSH), that is to say, besides the interannual anddecadal time scales, the WPSH would possess the circulation mode on longer timescales. For example, we may discuss the change of the WPSH in the whole Holocene epoch, i.e., the half precession period. These discussions could make sense to the study of not only the paleoclimate but also the modern climate.
48 citations
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TL;DR: This study provides a comprehensive analysis of trends in the extremes during the Indian summer monsoon months (June to September) at different temporal and spatial scales using quantile regression to identify and quantify spatiotemporal patterns and trends that have emerged during the recent decades and may be associated with changing climatic conditions.
Abstract: In this study, we provide a comprehensive analysis of trends in the extremes during the Indian summer monsoon (ISM) months (June to September) at different temporal and spatial scales. Our goal is to identify and quantify spatiotemporal patterns and trends that have emerged during the recent decades and may be associated with changing climatic conditions. Our analysis primarily relies on quantile regression that avoids making any subjective choices on spatial, temporal, or intensity pattern of extreme rainfall events. Our analysis divides the Indian monsoon region into climatic compartments that show different and partly opposing trends. These include strong trends towards intensified droughts in Northwest India, parts of Peninsular India, and Myanmar; in contrast, parts of Pakistan, Northwest Himalaya, and Central India show increased extreme daily rain intensity leading to higher flood vulnerability. Our analysis helps explain previously contradicting results of trends in average ISM rainfall.
46 citations
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TL;DR: In this article, the authors assess the spatial patterns in the trends of annual and seasonal rainfall amounts and extremes in Peninsular Malaysia considering Long-Term Persistence (LTP) in hydroclimatic time series, which can lead to considerable change in the significance of trend.
Abstract: The presence of long-term persistence (LTP) in hydroclimatic time series can lead to considerable change in the significance of trend. Therefore, past findings of climatic trend analysis without considering LTP in time series has become a disputable issue. The objective of this study was to assess the spatial patterns in the trends of annual and seasonal rainfall amounts and extremes in Peninsular Malaysia considering LTP. Daily rainfall data of APHRODITE (Asian Precipitation – Highly-Resolved Observational Data Integration Towards Evaluation) for the period 1951–2007 was used to assess the trends using the classical Mann–Kendall (MK) test and the modified version of the MK test, which can remove the influence of LTP in the significance of trends. The results indicate that significant trends in different rainfall indices of Peninsular Malaysia obtained using the MK test reduced drastically when LTP was taken into consideration. There was almost no change in annual and seasonal rainfall amounts, which contradicts the findings of previous studies. The field significance of regional trends revealed an increase in wet spells at an average rate of 4.8 and 4.9 days/decade in the southeast and the southwest respectively during the northeast monsoon, and a decrease in rainy days by −1.4 days/decade in the north and an increase both in dry spells by 1.0 day/decade in the southeast and in the maximum 1 day rainfall by 1.7 mm/decade on the west coast during the southwest monsoon. The results indicate that the trends in rainfall indices reported in the maritime continent in previous studies should be re-evaluated as most of them are due to LTP.
43 citations
Cites background from "Long-Term (1951–2007) Rainfall Tren..."
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TL;DR: In this article, the authors used Ridge Regression (RR) method to analyze the relationship between seasonal variations of precipitation, surface winds speed, air temperature, and Enhanced Vegetation Index (EVI) with Dust Storm Index (DSI) for two different periods (2001-2008 and 2009-2016).
Abstract: Atmospheric conditions and physical characteristics of the earth surface have an important effect on the spatiotemporal variations of sand-dust events. The main objective of the present study was to investigate the effect of these variables on the seasonal variation of these events in semi-arid regions of Central Iran Zone (CIZ). The Ridge Regression (RR) method was used to analyze the relationship between seasonal variations of precipitation, surface winds speed, air temperature, and Enhanced Vegetation Index (EVI) with Dust Storm Index (DSI) for two different periods (2001–2008 and 2009–2016). The dusty winds direction around the study area was also determined using the dust roses. The results showed that the annual DSI changes in the study area had a week incremental trend with a rate of 0.07/8 yrs in the previous period while it followed a strong increasing trend with a rate of 0.22/8 yrs in the latter period. It was also found that the activity of sand-dust storms in the second period was greater than the first period, especially in the border region of Iran and Turkmenistan. According to RR analysis, DSI had a significant positive association with the surface winds speed in the summer (β = +0.48; p-value 0.05). In the second period, the surface winds speed was positively correlated with the DSI in the spring (β = +2.04), summer (β = +2.6) and autumn (β = +2.08). The significant negative relationship between EVI and DSI changes was observed only in the spring season (β = −0.7; p-value
31 citations
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TL;DR: Temporal evolution, source apportionment and transport pathways of particulate matter (PM2.5 and PM10) are analyzed over Guwahati, located in the Brahmaputra River Valley (BRV), as a function of meteorological dynamics as discussed by the authors.
Abstract: Temporal evolution, source apportionment and transport pathways of particulate matter (PM2.5 and PM10) are analysed over Guwahati, located in the Brahmaputra River Valley (BRV), as a function of meteorological dynamics. During the study period (July 2013–June 2014), the mean PM2.5 and PM10 mass concentrations were found to be 52 ± 37 and 91 ± 60 μg m−3, respectively, both exhibiting higher concentrations during December–March and very low during summer. The annual mean ratio of PM2.5/PM10 was 0.57 ± 0.11, varying from 0.24 to 0.86, suggesting dominance of anthropogenic vs natural emissions during winter and spring, respectively. Diurnal variation reveals higher PM concentrations during morning (∼9:00 local time (LT)) and evening (∼23:00 LT) and lowest around ∼14:00 to 17:00 LT due to influence of dilution processes and higher mixing-layer height over the region. Bivariate plots and Conditional Bivariate Probability Function (CBPF) analysis showed that the highest PM2.5 and PM10 concentrations are mostly associated with weak northwestern winds (
29 citations
References
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01 Jan 1968
TL;DR: In many fields using empirical areal data there arises a need for interpolating from irregularly-spaced data to produce a continuous surface as discussed by the authors, and it is assumed that a unique number (such as rainfall in meteorology, or altitude in geography) is associated with each data point.
Abstract: In many fields using empirical areal data there arises a need for interpolating from irregularly-spaced data to produce a continuous surface. These irregularly-spaced locations, hence referred to as “data points,” may have diverse meanings: in meterology, weather observation stations; in geography, surveyed locations; in city and regional planning, centers of data-collection zones; in biology, observation locations. It is assumed that a unique number (such as rainfall in meteorology, or altitude in geography) is associated with each data point. In order to display these data in some type of contour map or perspective view, to compare them with data for the same region based on other data points, or to analyze them for extremes, gradients, or other purposes, it is extremely useful, if not essential, to define a continuous function fitting the given values exactly. Interpolated values over a fine grid may then be evaluated. In using such a function it is assumed that the original data are without error, or that compensation for error will be made after interpolation.
3,433 citations
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TL;DR: Human activities are releasing tiny particles (aerosols) into the atmosphere that enhance scattering and absorption of solar radiation, which can lead to a weaker hydrological cycle, which connects directly to availability and quality of fresh water, a major environmental issue of the 21st century.
Abstract: Human activities are releasing tiny particles (aerosols) into the atmosphere. These human-made aerosols enhance scattering and absorption of solar radiation. They also produce brighter clouds that are less efficient at releasing precipitation. These in turn lead to large reductions in the amount of solar irradiance reaching Earth's surface, a corresponding increase in solar heating of the atmosphere, changes in the atmospheric temperature structure, suppression of rainfall, and less efficient removal of pollutants. These aerosol effects can lead to a weaker hydrological cycle, which connects directly to availability and quality of fresh water, a major environmental issue of the 21st century.
3,167 citations
"Long-Term (1951–2007) Rainfall Tren..." refers background in this paper
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TL;DR: In this article, the effects of aerosols on the climate system are discussed and different approaches how the climatic implications of these effects can be estimated globally as well as improvements that are needed in global climate models in order to better represent indirect aerosol effects are discussed.
Abstract: . Aerosols affect the climate system by changing cloud characteristics in many ways. They act as cloud condensation and ice nuclei, they may inhibit freezing and they could have an influence on the hydrological cycle. While the cloud albedo enhancement (Twomey effect) of warm clouds received most attention so far and traditionally is the only indirect aerosol forcing considered in transient climate simulations, here we discuss the multitude of effects. Different approaches how the climatic implications of these aerosol effects can be estimated globally as well as improvements that are needed in global climate models in order to better represent indirect aerosol effects are discussed in this paper.
2,208 citations
"Long-Term (1951–2007) Rainfall Tren..." refers background in this paper
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TL;DR: In this article, precipitation intensity, duration, frequency, and phase are as much of concern as total amounts, as these factors determine the disposition of precipitation once it hits the ground and how much runs off.
Abstract: From a societal, weather, and climate perspective, precipitation intensity, duration, frequency, and phase are as much of concern as total amounts, as these factors determine the disposition of precipitation once it hits the ground and how much runs off. At the extremes of precipitation incidence are the events that give rise to floods and droughts, whose changes in occurrence and severity have an enormous impact on the environment and society. Hence, advancing understanding and the ability to model and predict the character of precipitation is vital but requires new approaches to examining data and models. Various mechanisms, storms and so forth, exist to bring about precipitation. Because the rate of precipitation, conditional on when it falls, greatly exceeds the rate of replenishment of moisture by surface evaporation, most precipitation comes from moisture already in the atmosphere at the time the storm begins, and transport of moisture by the storm-scale circulation into the storm is vital....
2,133 citations
"Long-Term (1951–2007) Rainfall Tren..." refers background in this paper
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TL;DR: It will be substantially harder to quantify the range of possible changes in the hydrologic cycle than in global-mean temperature, both because the observations are less complete and because the physical constraints are weaker.
Abstract: What can we say about changes in the hydrologic cycle on 50-year timescales when we cannot predict rainfall next week? Eventually, perhaps, a great deal: the overall climate response to increasing atmospheric concentrations of greenhouse gases may prove much simpler and more predictable than the chaos of short-term weather. Quantifying the diversity of possible responses is essential for any objective, probability-based climate forecast, and this task will require a new generation of climate modelling experiments, systematically exploring the range of model behaviour that is consistent with observations. It will be substantially harder to quantify the range of possible changes in the hydrologic cycle than in global-mean temperature, both because the observations are less complete and because the physical constraints are weaker.
1,996 citations
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