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1.
Some characteristics of very heavy rainfall over Orissa during summer monsoon season 总被引:1,自引:0,他引:1
Orissa is one of the most flood prone states of India. The floods in Orissa mostly occur during monsoon season due to very
heavy rainfall caused by synoptic scale monsoon disturbances. Hence a study is undertaken to find out the characteristic features
of very heavy rainfall (24 hours rainfall ≥125 mm) over Orissa during summer monsoon season (June–September) by analysing
20 years (1980–1999) daily rainfall data of different stations in Orissa. The principal objective of this study is to find
out the role of synoptic scale monsoon disturbances in spatial and temporal variability of very heavy rainfall over Orissa.
Most of the very heavy rainfall events occur in July and August. The region, extending from central part of coastal Orissa
in the southeast towards Sambalpur district in the northwest, experiences higher frequency and higher intensity of very heavy
rainfall with less interannual variability. It is due to the fact that most of the causative synoptic disturbances like low
pressure systems (LPS) develop over northwest (NW) Bay of Bengal with minimum interannual variation and the monsoon trough
extends in west-northwesterly direction from the centre of the system. The very heavy rainfall occurs more frequently with
less interannual variability on the western side of Eastern Ghat during all the months and the season except September. It
occurs more frequently with less interannual variability on the eastern side of Eastern Ghat during September. The NW Bay
followed by Gangetic West Bengal/Orissa is the most favourable region of LPS to cause very heavy rainfall over different parts
of Orissa except eastern side of Eastern Ghat. The NW Bay and west central (WC) Bay are equally favourable regions of LPS
to cause very heavy rainfall over eastern side of Eastern Ghat. The frequency of very heavy rainfall does not show any significant
trend in recent years over Orissa except some places in north-east Orissa which exhibit significant rising trend in all the
monsoon months and the season as a whole. 相似文献
2.
D. R. Pattanaik 《Natural Hazards》2007,40(3):635-646
Between 1941 and 2002 there has been a decreasing trend in the frequency of monsoon disturbances (MDs) during the summer monsoon
season (June–September). This downwards trend is significant at the 99.9% level for the main monsoon phase (July–August) and
the withdrawal phase (September); however, it is not significant during the onset phase (June). The variability in rainfall
over the homogeneous regions of India on the sub-seasonal scale also shows a significant decreasing trend with respect to
the amount of rainfall over Northwest India (NWI) and Central India (CEI) during all three phases of the monsoon. Meteorological
observations reveal that there has been an eastward shift of the rainfall belt with time over the Indian region on the seasonal
scale and that this shift is more prominent during the withdrawal phase. This decreasing trend in MDs together with its restricted
westerly movement seem to be directly related to the decreasing trend in rainfall over CEI during both the main monsoon and
withdrawal phases and over NWI during the withdrawal phase. The low-level circulation anomalies observed during two periods
(period-I: 1951–1976; period-ii: 1977–2002) are in accordance with the changes in rainfall distribution, with comparatively
more (less) rainfall falling over NWI, CEI and Southern Peninsular India (SPI) during period-I (period-ii), and are accompanied
by a stronger (weaker) monsoon circulation embedded with an anomalous cyclonic (anti-cyclonic) circulation over CEI during
the main monsoon and withdrawal phases. During the onset phase, completely opposite circulation anomalies are observed during
both periods, and these are associated with more (less) rainfall over NWI, CEI and SPI during period-ii (period-I). 相似文献
3.
Spatio-temporal variability of summer monsoon rainfall over Orissa in relation to low pressure systems 总被引:2,自引:0,他引:2
The summer monsoon rainfall over Orissa occurs mostly due to low pressure systems (LPS) developing over the Bay of Bengal
and moving along the monsoon trough. A study is hence undertaken to find out characteristic features of the relationship between
LPS over different regions and rain-fall over Orissa during the summer monsoon season (June-September). For this purpose,
rainfall and rainy days over 31 selected stations in Orissa and LPS days over Orissa and adjoining land and sea regions during
different monsoon months and the season as a whole over a period of 20 years (1980-1999) are analysed. The principal objective
of this study is to find out the role of LPS on spatial and temporal variability of summer monsoon rainfall over Orissa.
The rainfall has been significantly less than normal over most parts of Orissa except the eastern side of Eastern Ghats during
July and hence during the season as a whole due to a significantly less number of LPS days over northwest Bay in July over
the period of 1980-1999. The seasonal rainfall shows higher interannual variation (increase in coefficient of variation by
about 5%) during 1980-1999 than that during 1901-1990 over most parts of Orissa except northeast Orissa. Most parts of Orissa,
especially the region extending from central part of coastal Orissa to western Orissa (central zone) and western side of the
Eastern Ghats get more seasonal monsoon rainfall with the development and persistence of LPS over northwest Bay and their
subsequent movement and persistence over Orissa. The north Orissa adjoining central zone also gets more seasonal rainfall
with development and persistence of LPS over northwest Bay. While the seasonal rainfall over the western side of the Eastern
Ghats is adversely affected due to increase in LPS days over west central Bay, Jharkhand and Bangladesh, that over the eastern
side of the Eastern Ghats is adversely affected due to increase in LPS days over all the regions to the north of Orissa. There
are significant decreasing trends in rainfall and number of rainy days over some parts of southwest Orissa during June and
decreasing trends in rainy days over some parts of north interior Orissa and central part of coastal Orissa during July over
the period of 1980-1999 相似文献
4.
Nityanand Singh 《Journal of Earth System Science》1995,104(1):1-36
Large-scale interannual variability of the northern summer southwest monsoon over India is studied by examining its variation
in the dry area during the period 1871–1984. On the mean summer monsoon rainfall (June to September total) chart the 800 mm
isohyet divides the country into two nearly equal halves, named as dry area (monsoon rainfall less than 800 mm) and wet area
(monsoon rainfall greater than 800 mm). The dry area/wet area shows large variations from one year to another, and is considered
as an index for assessing the large-scale performance of the Indian summer monsoon. Statistical and fluctuation characteristics
of the summer monsoon dry area (SMDA) are reported.
To identify possible causes of variation in the Indian summer monsoon, the correlation between the summer monsoon dry area
and eleven regional/global circulation parameters is examined. The northern hemisphere surface air temperature, zonal/hemispheric/global
surface air and upper air temperatures, Southern Oscillation, Quasi-biennial oscillation of the equatorial lower stratosphere,
April 500-mb ridge along 75°E over India, the Indian surface air temperature and the Bombay sea level pressure showed significant
correlation.
A new predictor parameter that is preceding year mean monsoon rainfall of a few selected stations over India has been suggested
in the present study. The stations have been selected by applying the objective technique ‘selecting a subset of few gauges
whose mean monsoon rainfall of the preceding year has shown the highest correlation coefficient (CC) with the SMDA’. Bankura
(Gangetic West Bengal), Cuddalore (Tamil Nadu) and Anupgarh (West Rajasthan) entered the selection showing a CC of 0.724.
Using a dependent sample of 1951–1980 a predictive model (multiple CC = 0.745) has also been developed for the SMDA with preceding
year mean monsoon rainfall of the three selected stations and the sea level pressure tendency at Darwin from Jan–Feb to Mar–May
as independent parameters. 相似文献
5.
The present study examines the characteristics and climatological features of daily rainfall data over Andaman & Nicobar Islands. Analysis of rainfall data reveals a large monthly deviation over the northern latitudes as compare to southern latitudes of Andaman & Nicobar Islands. Also, it is found that rainfall increases from north to south latitudes in all the seasons except monsoon, where a reverse pattern exists. In trend analysis, a statistically significant decreasing trend (confidence level >95?%) is observed for yearly rainfall and rainy days over the region. Analysis of daily rainfall intensity for each year shows increasing trend for frequency of rather heavy rain (35.6?C64.4?mm) and significant decreasing trend for frequencies of light rain (2.5?C7.5?mm), and very heavy rain (>124.5?mm) over the region. Many times, very heavy rain events are associated with cyclonic disturbances affecting Andaman & Nicobar Islands region. The analysis of cyclonic disturbances over the region reveals a stronger and more significant decreasing trend. So, one of the causes for decreasing trend in very heavy rain over Andaman & Nicobar Islands may be due to significant decreasing frequency of cyclonic disturbances affecting this region. 相似文献
6.
SAVITA PATWARDHAN ASHWINI KULKARNI K KRISHNA KUMAR 《Journal of Earth System Science》2012,121(1):203-210
A state-of-the-art regional climate modelling system, known as PRECIS (Providing REgional Climates for Impacts Studies) developed
by the Hadley Centre for Climate Prediction and Research, UK is applied over the Indian domain to investigate the impact of
global warming on the cyclonic disturbances such as depressions and storms. The PRECIS simulations at 50 × 50 km horizontal
resolution are made for two time slices, present (1961–1990) and the future (2071–2100), for two socioeconomic scenarios A2
and B2. The model simulations under the scenarios of increasing greenhouse gas concentrations and sulphate aerosols are analysed
to study the likely changes in the frequency, intensity and the tracks of cyclonic disturbances forming over north Indian
Ocean (Bay of Bengal and Arabian Sea) and the Indian landmass during monsoon season. The model overestimates the frequency
of cyclonic disturbances over the Indian subcontinent in baseline simulations (1961–1990). The change is evaluated towards
the end of present century (2071–2100) with respect to the baseline climate. The present study indicates that the storm tracks
simulated by the model are southwards as compared to the observed tracks during the monsoon season, especially for the two
main monsoon months, viz., July and August. The analysis suggests that the frequency of cyclonic disturbances forming over
north Indian Ocean is likely to reduce by 9% towards the end of the present century in response to the global warming. However,
the intensity of cyclonic disturbances is likely to increase by about 11% compared to the present. 相似文献
7.
G. Nageswara Rao 《Journal of Earth System Science》1999,108(4):327-332
Rainfall variability over a river basin has greater impact on the water resource in that basin. With this in view, the variability
of the monsoon rainfall over the Godavari river basin has been studied on different time scales. As expected, the monsoon
rainfall in Godavari basin is more variable (17%) than the all-India monsoon rainfall (11%) during the period of study (1951–90).
Similarly, inter-annual variability of the monsoon rainfall on smaller time scales is found to be still higher and increases
while going on from seasonal to daily scales. An interesting observation is that the intra-seasonal variability of the monsoon
rainfall has a significant negative relationship (CC= −0.53) with the total seasonal rainfall in the basin. 相似文献
8.
Some statistical properties of the summer monsoon seasonal rainfall for India during the last 100 years (1881–1980) are presented.
The most recent decade of 1971–1980 shows the lowest value of standard-decadal average monsoon rainfall (86.40 cm) and is
also characterised by the second highest value of coefficient of variation in monsoon rainfall (12.4 %). The combined last
two standard-decadal period of 1961–1980 was the period of the largest coefficient of variation and the lowest average monsoon
rainfall for India.
The possible influence of global climatic variability on the performance of the monsoon is also examined. Analyses of correlation
coefficient show that a statistically significant positive relationship with a time-lag of about six months exists between
monsoon rainfall and northern hemispheric surface air temperature. A cooler northern hemisphere during January/February leads
to a poor monsoon.
All the major drought years during the last 3 decades had much cooler January/February periods over the northern hemisphere—1972
having the coldest January/February with a temperature departure of −0.94°C and the most disastrous monsoon failure. 相似文献
9.
Deng-Hua Yan Dong-Mei Han Gang Wang Yong Yuan Yong Hu Hong-yang Fang 《Natural Hazards》2014,73(2):849-858
Based on the daily precipitation data of 38 weather stations in the Huai River Basin from 1961 to 2010, this study used SPI index, P-III curve to determine the flood/drought years, under what situations for droughts and floods easily happen, and to analyze the evolution law of flood and drought during inter-annual and intra-annual based on the characteristic of monthly precipitation. The results showed that: (1) annual rainfall of the Huai River Basin presented decreasing trend, maximum rainfall appeared from June to August, and multi-year average precipitation increased gradually from north to south; (2) the variation of monthly precipitation during flood years was more severe than other typical years, and precipitation in drought years showed nearly 50 % decline compared with normal years; (3) high rainfall of flood years was mainly caused by the increase in rainfall in flood season, and the strategy of flood control and drought relief was “short-term flood prevention and long-term drought relief”; (4) while precipitation of most months in drought year was reduced, the relevant strategies “annual basin-wide of long-term drought prevention” should be carried out; (5) combination events of floods and droughts occurred frequently. Persistent drought dominated in spring and summer while droughts and floods that happened alternately were mainly in summer and autumn. 相似文献
10.
The interannual variability of all-India summer monsoon (June to September) rainfall and its teleconnections with the southern
oscillation index (SOI) and sea surface temperature (SST) anomaly of the eastern equatorial Pacific ocean have been examined for the period 1871–1978 for different seasons (i.e.,
winter, spring, summer and autumn). The relationship (correlation coefficient) between all-India summer monsoon rainfall andSOI for different seasons is positive and highly significant. Further examination of 10-, 20- and 30-year sliding window lengths’
correlations, brings out the highly consistent and significant character of the relationships. The relationship between all-India
monsoon rainfall andSST for different seasons is negative and is significant at 1 % level or above. Drought years are characterised by negative anomalies
ofSOI and positive anomalies ofSST and vice versa with flood years. The relationship betweenSOI andSST is negative and significant at 0.1 % level.
The relationships between all-India summer monsoon rainfall,SOI and sst are expected to improve our understanding of the interannual variability of the summer monsoon. 相似文献
11.
《地学前缘(英文版)》2015,6(6)
Global warming and climate change is one of the most extensively researched and discussed topical issues affecting the environment.Although there are enough historical evidence to support the theory that climate change is a natural phenomenon,many research scientists are widely in agreement that the increase in temperature in the 20 th century is anthropologically related.The associated effects are the variability of rainfall and cyclonic patterns that are being observed globally.In Southeast Asia the link between global warming and the seasonal atmospheric flow during the monsoon seasons shows varying degree of fuzziness.This study investigates the impact of climate change on the seasonality of monsoon Asia and its effect on the variability of monsoon rainfall in Southeast Asia.The comparison of decadal variation of precipitation and temperature anomalies before the 1970 s found general increases which were mostly varying.But beyond the 1970 s,global precipitation anomalous showed increases that almost corresponded with increases in global temperature anomalies for the same period.There are frequent changes and a shift westward of the Indian summer monsoon.Although precipitation is observed to be 70%below normal levels,in some areas the topography affects the intensity of rainfall.These shifting phenomenon of other monsoon season in the region are impacting on the variability of rainfall and the onset of monsoons in Southeast Asia and is predicted to delay for 15 days the onset of the monsoon in the future.The variability of monsoon rainfall in the SEA region is observed to be decadal and the frequency and intensity of intermittent flooding of some areas during the monsoon season have serious consequences on the human,financial,infrastructure and food security of the region. 相似文献
12.
The aim of this study was to investigate temporal variation in seasonal and annual rainfall trend over Ranchi district of Jharkhand, India for the period (1901–2014: 113 years). Mean monthly rainfall data series were used to determine the significance and magnitude of the trend using non-parametric Mann–Kendall and Sen’s slope estimator. The analysis showed a significant decreased in rainfall during annual, winter and southwest monsoon rainfall while increased in pre-monsoon and post-monsoon rainfall over the Ranchi district. A positive trend is detected in pre-monsoon and post-monsoon rainfall data series while annual, winter and southwest monsoon rainfall showed a negative trend. The maximum decrease in rainfall was found for monsoon (? 1.348 mm year?1) and minimum (? 0.098 mm year?1) during winter rainfall. The trend of post-monsoon rainfall was found upward (0.068 mm year?1). The positive and negative trends of annual and seasonal rainfall were found statistically non-significant except monsoon rainfall at 5% level of significance. Rainfall variability pattern was calculated using coefficient of variation CV, %. Post-monsoon rainfall showed the maximum value of CV (70.80%), whereas annual rainfall exhibited the minimum value of CV (17.09%), respectively. In general, high variation of CV was found which showed that the entire region is very vulnerable to droughts and floods. 相似文献
13.
Active and break spells of the Indian summer monsoon 总被引:6,自引:0,他引:6
In this paper, we suggest criteria for the identification of active and break events of the Indian summer monsoon on the basis
of recently derived high resolution daily gridded rainfall dataset over India (1951–2007). Active and break events are defined
as periods during the peak monsoon months of July and August, in which the normalized anomaly of the rainfall over a critical
area, called the monsoon core zone exceeds 1 or is less than −1.0 respectively, provided the criterion is satisfied for at
least three consecutive days. We elucidate the major features of these events. We consider very briefly the relationship of
the intraseasonal fluctuations between these events and the interannual variation of the summer monsoon rainfall. 相似文献
14.
The time evolution of atmospheric parameters on intraseasonal time scale in the eastern Arabian Sea (EAS) is studied during
the summer monsoon seasons of 1998–2003 using Tropical Rainfall Measuring Mission Microwave Imager (TMI) data. This is done
using the spectral and wavelet analysis. Analysis shows that over EAS, total precipitable water vapour (TWV) and sea surface
wind speed (SWS) have a periodicity of 8–15 days, 15–30 days and 30–60 days during the monsoon season. Significant power is
seen in the 8–15-day time scale in TWV during onset and retreat of the summer monsoon. Analysis indicates that the timings
of the intensification of 8–15, 15–30, and 30–60 days oscillations have a profound effect on the evolution of the daily rainfall
over west coast of India. The positive and negative phases of these oscillations are directly related to the active and dry
spells of rainfall along the west coast of India. The spectral analysis shows interannual variation of TWV and SWS. Heavy
rainfall events generally occur over the west coast of India when positive phases of both 30–60 days and 15–30 days modes
of TWV and SWS are simultaneously present. 相似文献
15.
16.
Geomorphic Effects of Monsoon Floods on Indian Rivers 总被引:1,自引:0,他引:1
The southwest summer monsoon contributesthe bulk of India's rainfall. Consequently,almost all the geomorphic work by the rivers is carried out during the monsoonseason in general and the monsoon floods in particular. Indian rivers arecharacterized by high average flood discharges and large temporal variability. Thereis also significant spatial variation in the magnitude, frequency and power of floods, on account of regional variations in monsoon rainfall, basin characteristics andchannel geometry. As a result, the channel responses and the geomorphic effects also varyspatially. This paper describes the hydrological and geomorphological aspects, as well asthe geomorphic effects of monsoon floods in the Indian rivers. The geomorphic effects of floods are most impressive only in certainareas – the Himalaya, the Thar Desert, and the Indus-Ganga-Brahmaputra Plains. There are numerous instances of flood-induced changes in the channel dimension,position and pattern in these areas. In the Ganga-Brahmaputra Plains, the annualfloods appear to be geomorphologically more effective than the occasional large floods.In comparison, the rivers of the Indian Peninsula are, by and large, stable and thegeomorphic effects of floods are modest. Only large-magnitude floods that occur at aninterval of several years to decades are competent to modify the channel morphology in asignificant way. A synthesis of the various case studies available from the Indianregion indicates that often the absolute magnitude of a flood is not as important withrespect to the geomorphic effects as the flow stress and competence. 相似文献
17.
On the impacts of ENSO and Indian Ocean dipole events on sub-regional Indian summer monsoon rainfall 总被引:3,自引:0,他引:3
The relative impacts of the ENSO and Indian Ocean dipole (IOD) events on Indian summer (June–September) monsoon rainfall at
sub-regional scales have been examined in this study. GISST datasets from 1958 to 1998, along with Willmott and Matsuura gridded
rainfall data, all India summer monsoon rainfall data, and homogeneous and sub-regional Indian rainfall datasets were used.
The spatial distribution of partial correlations between the IOD and summer rainfall over India indicates a significant impact
on rainfall along the monsoon trough regions, parts of the southwest coastal regions of India, and also over Pakistan, Afghanistan,
and Iran. ENSO events have a wider impact, although opposite in nature over the monsoon trough region to that of IOD events.
The ENSO (IOD) index is negatively (positively) correlated (significant at the 95% confidence level from a two-tailed Student
t-test) with summer monsoon rainfall over seven (four) of the eight homogeneous rainfall zones of India. During summer, ENSO
events also cause drought over northern Sri Lanka, whereas the IOD events cause surplus rainfall in its south. On monthly
scales, the ENSO and IOD events have significant impacts on many parts of India. In general, the magnitude of ENSO-related
correlations is greater than those related to the IOD. The monthly-stratified IOD variability during each of the months from
July to September has a significant impact on Indian summer monsoon rainfall variability over different parts of India, confirming
that strong IOD events indeed affect the Indian summer monsoon.
相似文献
Karumuri AshokEmail: |
18.
P. V. Joseph Anu Simon Venu G. Nair Aype Thomas 《Journal of Earth System Science》2004,113(2):139-150
Time series of daily averaged rainfall of about 40 rain gauge stations of south Kerala, situated at the southern-most part
of peninsular India between latitudes about 8‡N and 10‡N were subjected to Wavelet Analysis to study the Intra Seasonal Oscillation
(ISO) in the rainfall and its inter-annual variability. Of the 128 days, 29th May to 3rd October of each of the 95 years 1901-1995
were analysed. We find that the period of ISO does not vary during a monsoon season in most of the years, but it has large
inter-annual variability in the range 23 to 64 days. Period-wise, the years cluster into two groups of ISO, the SHORT consisting
of periods 23, 27 and 32 days and the LONG with a single period of 64 days, both the sets at a significance level of 99%.
During the 95 years at this level of significance there are 44 years with SHORT and 20 years with LONG periods. 11 years have
no ISO even at the 90% level of significance.
We composited NCEP SST anomalies of the summer monsoon season June to September for two groups of years during the period
1965–1993. The first group is of 5 years with a LONG ISO period of 64 days for south Kerala rainfall at significance level
of 99% and the second group is of 12 years with SHORT ISO periods of 23, 27 and 32 days at the same level of significance.
The SST anomaly for the LONG (SHORT) ISO resembles that for an El Nino (La Nina). 相似文献
19.
The anomalies of summer rainfall (June–August) for the last 500 years in China have been estimated according to the relationship
between the instrumentally observed rainfall and the degrees of floods and droughts for the last 25 years. It is shown that
calculated anomalies of average rainfall for 10, 20 and 30 year periods have sufficient accuracies. The long-term climatic
variations for the last 500 years are discussed based on the estimated anomalies of summer rainfall of 25 stations over the
E part of China for the last 500 years. For example, there were prolonged drought in the N of China at about the end of Ming
dynasty, but there were extensive floods in China for the early times of Qing dynasty. The anomalies of rainfall for the last
500 years were averaged along latitude zone and their decade running mean were formed. It was found that the long-term variations
are very clear. The 80 year cycle is predominating. Besides, an about 200 year cycle is also shown in the charts of 50-year
mean rainfall anomalies. It is indicated that both above mentioned cycles relate closely to the solar activity. 相似文献
20.
Bushra Khalid Débora Souza Alvim Shumaila Javeed Junaid Aziz Khan Muhammad Asif Javed Azmat Hayat Khan 《Natural Hazards》2018,92(2):971-993
Pakistan has experienced severe floods over the past decades due to climate variability. Among all the floods, the flood of 2010 was the worst in history. This study focuses on the assessment of (1) riverine flooding in the district Jhang (where Jhelum and Chenab rivers join, and the district was severely flood affected) and (2) south Asiatic summer monsoon rainfall patterns and anomalies considering the case of 2010 flood in Pakistan. The land use/cover change has been analyzed by using Landsat TM 30 m resolution satellite imageries for supervised classification, and three instances have been compared, i.e., pre-flooding, flooding, and post-flooding. The water flow accumulation, drainage density and pattern, and river catchment areas have been calculated by using Shutter Radar Topography Mission digital elevation model 90 m resolution. The standard deviation of south Asiatic summer monsoon rainfall patterns, anomalies and normal (1979–2008) has been calculated for July, August, and September by using rainfall data set of Era interim (0.75° × 0.75° resolution). El Niño Southern Oscillation has also been considered for its role in prevailing rainfall anomalies during the year 2010 over Upper Indus Basin region. Results show the considerable changing of land cover during the three instances in the Jhang district and water content in the rivers. Abnormal rainfall patterns over Upper Indus Basin region prevailed during summer monsoon months in the year 2010 and 2011. The El Niño (2009–2010) and its rapid phase transition to La Niña (2011–2012) may be the cause of severity and disturbances in rainfall patterns during the year 2010. The Geographical Information System techniques and model based simulated climate data sets have been used in this study which can be helpful in developing a monitoring tool for flood management. 相似文献