Probabilities of excess and deficient southwest monsoon rainfall over different meteorological sub-divisions of India

Temporal distribution of southwest monsoon (June - September) rainfall is very useful for the country's agriculture and food grain production. It contributes more than 75 of India's annual rainfall. In view of this, an attempt has been made here to understand the performance of the monthly rainfall for June, July, August and September when the seasonal rainfall is reported as excess, deficient or normal. To know the dependence of seasonal rainfall on monthly rainfall, the probabilities of occurrence of excess, deficient and normal monsoon when June, July, August and also June + July and August + September rainfall is reported to be excess or deficient, are worked out using the long homogenous series of 124 years (18711994) data of monthly and seasonal rainfall of 29 meteorological sub-divisions of the plain regions of India. In excess monsoon years, the average percentage contribution of each monsoon month to the long term mean (1871-1994) seasonal rainfall (June - September) is more than that of the normal while in the deficient years it is less than normal. This is noticed in all 29 meteorological sub-divisions. From the probability analysis, it is seen that there is a rare possibility of occurrence of seasonal rainfall to be excess/deficient when the monthly rainfall of any month is deficient/excess

Intra-seasonal, inter-annual and decadal scale variability in summer monsoon rainfall over India

Using daily rainfall data for the 30-year period of 1960-1989 and following an objective criterion, the pre-active, active and post-active phases of the summer monsoon (June-September) rainfall are clearly delineated for all-India and homogeneous regions of India. It is seen that on average, the monsoon is active for 103 days over northeast (NE-India) India, for 75-78 days over central-northeast (CNE-India) India and so on for all the regions. Average daily normal rainfall (ADNRF) is at a maximum of 14.7 mm over NE-India and at a minimum of 4.6 mm over NW-India. To investigate possible periodic oscillations in daily rainfall, the daily normal rainfall (DNRF) of all the regions is subjected to power spectrum analysis. This analysis reveals that DNRF exhibits periodicities of 5, 8-12 and 20 days over NE-India, about 5 and 40 days over WC-India, 8-12 and 40 days over NW-India and 8-10 and 40 days over PEN-India. Inter-annual and decadal scale variability of the summer monsoon rainfall over homogeneous regions is studied using the summer monsoon rainfall for the period of 1871-1990. It is discovered that summer monsoon rainfall of WC-India and NW-India is dominated by a quasi-biennial oscillation (QBO), whereas summer monsoon rainfall of NE-India and PEN-India is dominated by ENSO-type periodicities. Epochs of increasing and decreasing rainfall are also observed in the summer monsoon rainfall over homogeneous regions of India

On the recent changes in surface temperature trends over India

Marked differences from global trends in terms of diurnal asymmetry of temperature trends were reported earlier for India, indicating that the warming over India was solely contributed by maximum temperatures. We report substantial recent changes in the nature of trends, using updated data sets up to 2003, with special focus on the last three decades. While all-India mean annual temperature has shown significant warming trend of 0.05°C/10yr during the period 1901-2003, the recent period 1971-2003 has seen a relatively accelerated warming of 0.22°C/10yr, which is largely due to unprecedented warming during the last decade. Further, in a major shift, the recent period is marked by rising temperatures during the monsoon season, resulting in a weakened seasonal asymmetry of temperature trends reported earlier. The recent accelerated warming over India is manifest equally in daytime and nighttime temperatures

Recent trends in pre-monsoon daily temperature extremes over India

Extreme climate and weather events are increasingly being recognized as key aspects of climate change. Pre-monsoon season (March-May) is the hottest part of the year over almost the entire South Asian region, in which hot weather extremes including heat waves are recurring natural hazards having serious societal impacts, particularly on human health. In the present paper, recent trends in extreme temperature events for the pre-monsoon season have been studied using daily data on maximum and minimum temperatures over a well-distributed network of 121 stations for the period 1970-2005. For this purpose, time series of extreme temperature events have been constructed for India as a whole and seven homogeneous regions, viz., Western Himalaya (WH), Northwest (NW), Northeast (NE), North Central (NC), East coast (EC), West coast (WC) and Interior Peninsula (IP). In general, the frequency of occurrence of hot days and hot nights showed widespread increasing trend, while that of cold days and cold nights has shown widespread decreasing trend. The frequency of the occurrence of hot days is found to have significantly increased over EC, WC and IP, while that of cold days showed significant decreasing trend over WH and WC. The three regions EC, WC and NW showed significant increasing trend in the frequency of hot nights. For India as whole, the frequency of hot days and nights showed increasing trend while cold days and nights showed decreasing trends. Day-to-day fluctuations of pre-monsoon daily maximum and minimum temperatures have also been studied for the above regions. The results show that there is no significant change in day-to-day magnitude of fluctuations of pre-monsoon maximum and minimum temperatures. However, the results generally indicate that the daily maximum and minimum temperatures are becoming less variable within the season

Long term temperature trends at major, medium, small cities and hill stations in India during the period 1901-2013

Industrialization and urbanization are the most dominant causal factors for long-term changes in surface air temperatures. To examine this fact, the long term changes in the surface-air temperatures have been evaluated by the linear trend for the different periods, i.e. 1901-2013, 1901-1970 and recent period 1971-2013 as rapid industrialization was observed during the recent four decades. In the present study, seasonal and annual mean, maximum and minimum temperature data of 36 stations for the period 1901-2013 have been used. These stations are classified into 4 groups, namely major, medium, small cities and hill stations. During the period 1901-1970, less than 50% stations from each group showed a significant increasing trend in annual mean temperature, whereas in the recent period 1971-2013, more than 80% stations from all the groups except small city group showed a significant increasing trend. The minimum temperature increased faster than that of the maximum temperature over major and medium cities, while maximum temperature increased faster than the minimum temperature over the small cities and hill stations. The annual mean temperature of all the coastal stations showed a significant increasing trend and positive correlation with Precipitable Water Vapour (PWV). The effect of PWV is more pronounced on minimum temperature than that of the maximum

Regression model for estimation of indian foodgrain production from summer monsoon rainfall

The agricultural economy of India with its large and growing population is closely linked to the performance of the summer monsoon rainfall over the country. For a recent 25-year period, 1961-1985, excellent All-India summer monsoon rainfall data and annual foodgrain production data are available and have been examined for their relationships. The influence of weather has been separated from the impact of technology on foodgrain production by fitting the exponential trend curve. The correlation coefficient (CC) between the percentage departure of All-India summer monsoon rainfall from average (P) and the total annual foodgrain production index (F) series is 0.82, which is significant at the 0.1 level. When data series are divided into two or three equal parts, the CCs are characterized by high stability and consistency. The regression equation between the two series is F = 0.58P + 101.05, which is statistically significant at the 0.1 level, accounting for 67 of the total variance. A contingency table showed the closeness of the positive association between P and F series and further indicated that F will be > 105 during excess monsoon years and < 96 during deficient years of All-India rainfall. It is possible, from this fitted line, to estimate the foodgrain production of the country a few months in advance; this information could be useful to agricultural or scientific communities for economic planning and Governmental policy making

Indian summer monsoon rainfall indices: 1871-1990

The paper describes some homogenous representations of the Indian summer monsoon rainfall for the period 1871-1990, prepared on the basis of a fixed and well-distributed network of 306 rain-gauges. An Indian Summer Monsoon Rainfall (ISMR) Index, indicating the net excess of deficient rainfall conditions over the country, is proposed. Statistical analysis of the above series identifies 18 large-scale dry years and 15 large-scale wet years during the last 120 yr. The decadal means of ISMR index were continuously negative for three decades 1901-30, positive 1931-60 and again became negative during the current period 1961-90

Surface air temperature variability over India during 1901-2007, and its association with enso

Seasonal and annual trends in surface air temperature over India and 7 homogeneous regions (western Himalaya, northwest, north-central, northeast, east coast, west coast and interior peninsula) were assessed during 3 periods: 1901–2007, 1971–2007 and 1998–2007. Indian annual mean (average of maximum and minimum), maximum and minimum temperatures showed significant warming trends of 0.51, 0.72 and 0.27°C 100 yr–1, respectively, during the period 1901–2007. However, accelerated warming was observed in the recent period 1971–2007, mainly due to intense warming in the recent decade 1998–2007. Temperatures (mean, maximum and minimum) increased by about 0.2°C per decade for the period 1971–2007, with a much steeper increase in minimum temperature than maximum temperature. In the most recent decade, maximum temperature was significantly higher compared to the long-term (1901–2007) mean, with a stagnated trend during this period, whereas minimum temperature showed an increasing trend, almost equal to that observed during 1971–2007. On a seasonal scale, pronounced warming trends in mean temperature were observed in winter and monsoon seasons, and a significant influence of El Niño Southern Oscillation events on temperature anomalies during certain seasons across India was observed. The composites of maximum and minimum temperatures of El Niño years showed positive anomalies during monsoon, post-monsoon and subsequent year winter and pre-monsoon seasons. However, statistically significant positive anomalies were observed only during monsoon and post-monsoon seasons over large areas of the country. The composite temperature anomalies of La Niña years were almost opposite to El Niño composites: the negative temperature anomalies associated with La Niña events persisted from the current monsoon season to the subsequent year pre-monsoon seaso

Changes in climate extremes over major river basins of India

Temporal changes in the extreme rainfall and temperature characteristics of major river basins on a daily time scale are examined using high-resolution gridded daily rainfall (1951–2014) and temperature (1951–2013) data sets. Trend analysis is carried out to examine the temporal changes in the frequency, area covered and intensity of the extreme rainfall and temperature events. Rainfall of 10 cm during southwest monsoon season (JJAS), maximum temperature of 40 °C during summer season (MAM) and minimum temperature of 10 °C during the winter season (DJF) have been used as the thresholds to define the extreme weather events of rainfall and temperature data in these river basins. Analysis indicates that during monsoon season zero rainfall days are increasing in all the river basins except some parts of the Krishna and Peninsular river basins. River basins located in the central parts of India show significant increase in the area covered by the heavy rainfall episodes and their intensity. Substantial rise in the monthly maximum temperatures is seen in the Krishna, Peninsular and West Coast river basins. Frequency, area coverage and intensity of hot days during summer season are increasing significantly in the Krishna and Peninsular river basins, while no substantial change has been observed for cold days during winter season in any river basins of the study