Breaks in monsoon and related precursors

A comprehensive analysis of eleven break monsoon situations that occurred during the period 1987 to 1997 have been attempted in the study. The various features like daily rainfall departures, wind anomalies and the satellite derived Outgoing Long wave Radiation (OLR) associated with the commencement/cessation of the break monsoon condition are studied with a view to identifying the precursors associate the break situation. The results reveal that there is progressive decrease of below normal rainfall departures 5 days prior to the actual break day in the latitude belts south of 20° N. During the period of the revival of the monsoon, the time section of the daily rainfall departures shows that the daily rainfall departure first starts becoming above normal in the southern most latitudinal belt 5° N to 10°N from the second day onwards after the cessation of the break. Similarly, the easterly anomalies in the zonal wind are first noticed in the southern latitude even 5 days prior to the starting of the break in the lower and middle troposphere. The maximum easterly anomalies in the lower and the middle troposphere move northwards upto 20° N. The composite latitudinal time section of OLR anomaly show a large area of negative OLR anomaly extending from 20°S to 10°N. The area is defined as the Southern. Hemispheric Convective Zone ( SHCZ). The negative OLR anomaly (10 Wm-2 is noticed around 5° S to 0° N. It increases to 20 Wm-2 on the second day of the break on the same latitudinal belt. The daily OLR anomaly pattern shows that the area of the negative OLR anomaly around the equatorial region increases with the approach of a break epoch. The forecasting aspects of the commencement / cessation of the break have been also discussed.

Probability of occurrence of drought in various sub-divisions of India

There are many studies dealing with interannual variability of rainfall in India. There are also studies available dealing with the reduction of food grain production during various drought years in India, Hence, there is along felt need to know about chances whether the next year will be a drought year. It is also seen that during last 11 years when the country as a whole experienced normal rainfall, there were few sub-divisions almost in each year facing a drought situation. The objective of this paper is to find out with the help of nearly 125 years data the probability of occurrence of drought in various sub-divisions of India and the probability of a sub-division facing two or more consecutive droughts, many studies deal with deficiency in all India summer monsoon rainfall and their linkage with El Nino. Effort has also been made in this paper to find out if there is any linkage between El Nino events in Pacific and meteorological drought in various sub-divisions of India. It is seen that eff~t of El Nino on each sub-division of India is different. It is also noticed that all El Nino years are not drought years and all drought years are also not El Nino years. During last 124 years there were 29 El Nino years. Out of these only 14 were drought years. Similarly there were 25 drought years during last 124 years out of which 11 drought years were not connected with El Nino.

Trends and periodicities in sub-divisional rainfall

The monthly and annual rainfall data for 35 meteorological sub-divisions for the 87-year period (1901-1987) have been used to study the trends and periodicities of monsoon and annual rainfall series. A number of distribution-free statistical tests have been applied to the rainfall series for testing non-randomness. Comparison of the decadewise means with the mean of the whole period showed that, for the country as a whole, the annual rainfall indicated four different climatic periods -two periods of above normal rainfall from 1960-1965 and from 1975 onwards and two periods of below normal rainfall from 1901-1915 and 1965-1975 whereas the monsoon rainfall showed two different climatic periods-a period of below normal rainfall from 1901-1920 and a period of above normal rainfall from 1920 onwards. The series were also subjected to low-passfilters which showed the presence of significant long term trend for a few sub-divisions. The power spectrum analysis for the annual and monthly rainfall series for a large number of sub-divisions showed significant periodicities of 2. 1-3.6 years, which correspond to the frequency range of the QBO. In addition, periodicities of 5.1 to 10.0 years and 19.3 years or more were also significant for a number of sub-divisions.

Effect of Hydrological Data on Flood Management in Urban Areas

Floods can occur due to rising water levels due to above-normal rainfall, changes in temperature, broken embankments/dams, rapid snowmelt, obstruction of water flow in other places, and putting people at risk of annual disasters due to flooding. The purpose of this study was to obtain a more detailed description of hydrological conditions so that flooding in the Bandar Lampung urban area can be optimally managed or controlled. The method used in flood control research is the analysis of the calculation of the average rainfall in the watershed, and the calculation of the planned discharge. The results of the analysis show that the existing drainage channels that have been carried out for each channel point have dimensions that are not large enough so that they are not sufficient to accommodate water runoff. so that for a 5-year discharge of 28.058 m3/s, the dimensions of the channel are 3 m wide and 2.6 m deep and for a 10-year discharge of 30.609 m3/s, the channel dimensions are 3.1 m wide and 2.7 m deep.

A statistical technique for determination of withdrawal of northeast monsoon over coastal Tamilnadu

The withdrawal dates of northeast monsoon over coastal Tamil Nadu for the 90-year period (1901-90) have been objectively derived. The methodology of determination was generally based on an index based on the spatial distribution of daily rainfall over stations of coastal Tamil Nadu, over a 5-day pentad for the six month period, September- February. The normal withdrawal date thus obtained was 27 December with a standard deviation of 13.6 days and range 23 November-28 January. The duration of northeast monsoon was distributed with mean 67.5 days, standard deviation 14.9 days and range 26-102 days. During 36.7 % of years the withdrawal spilled over to January of next year. The daily normal rainfall and its difference filter have been discussed with reference to the normal date of withdrawal. The average decrease of rainfall at the time of withdrawal has been derived by application of superposed epoch analysis. It has further been shown that during years when the withdrawal took place in January the intensity of northeast monsoon prior to withdrawal was as intense as in years when withdrawal occurred in December. A few cases of northeast monsoon withdrawal have been illustrated with diagrams. As no definite dynamic or thermodynamic features could be uniquely identified which are associated with the withdrawal, this technique is basically statistical, considering the behaviour of the daily normal rainfall as the sole criterion. Unique thermodynamic and dynamic features are not identifiable which are associated with the withdrawal of northeast monsoon over coastal Tamilnadu.

Characteristics of rainfall pattern for crop planning at Jabalpur region (Madhya Pradesh) of India

The daily rainfall data of past 31 years (1978-2008) of Agro meteorological Observatory, Department of Physics & Agriculture Engineering, Jabalpur (Madhya Pradesh) has been analyzed for establishing the long term average of weekly, monthly, seasonal and annual rainfall and its variability. The weekly probability of rainfall was estimated using Markov Chain probability model for receiving >= 10 and 30 mm rainfall per week. The mean annual rainfall observed as 1309 mm and its variability was 27.1 per cent. The highest annual and kharif season rainfall 2083 and 2052 mm respectively were recorded in 1994. On the other hand the lowest annual and kharif rainfall were 620 mm and 471 mm respectively in 1979. The study revealed that the recent decade rainfall has increased during last 31 years. The seasonal average kharif, post monsoon, winter and summer seasons recorded 1197.3 mm, 32.1 mm, 49.8 mm and 29.8 mm of rainfall. About 91.5 per cent of total annual rainfall was received in kharif, 2.5 per cent in post monsoon, 3.8 per cent in winter monsoon and 2.3 per cent in summer. During the period under study 16 per cent of the years recorded excess, 23 per cent deficit and 61 per cent normal rainfall. The July month is regarded as suitable for transplanting of rice crop in Jabalpur region. The highest contribution has been observed in August (33 per cent). Standard week from 25 to 37 received rainfall more than 30 mm indicating the crop growing period from June 2nd week to September last week.

Effect of monsoon depression of east coast at some distant region in west

Whenever a vortex or system of low or depression forms over head bay during Monsoon months, the west coast experiences heavy rainfall. These heavy rainfall occurrences are usually higher than the normal rainfall. An attempt has been made in this study to visualise the easterly wave model during monsoon months with the help of satellite imageries. The rain is expected heavy and wide spread over Madhya Maharashtra and South Gujarat when third sector of the wave covers these areas, as visualised in satellite wave and depression or vortex lies in the 5th or 6th sector of the wave.

A study on the characterization of monsoon rainfall for sorghum (Sorghum Vulgare Pers) and its response to typical rainfall patterns

Twenty eight years (1962-89) rainfall of Nagpur was analysed and the rainfall suitability at various probability levels for sorghum crop was studied. The total rainfall during kharif season (25-39th MW) was 861.50 mm. Normal rainfall/week exceeded 50 mm during 12 weeks (25-36th MW) which declined successively for three week (37-39th MW). The coefficient of variation (CY) ranged between 74.3% (25th MW), to 144.7% (39th MW). The rainfall at 50% probability level was well distrturbed during 12 week (25-36th MW)-ranging between 44.5 to 36.3 mm being adequate and sufficient (>20 mm/week) for sorghum crop considering its weekly demand (21-35 mm/week). Typical rainfall patterns representing the situation were defined on the basis of their repetitiveness. Out of four typical rainfall patterns studied the one with lowest rainfall (458.4 mm /season and 30.56 mm/week) fetched the highest yield (865.0 kg/ha) which ensured adequate rains during the various growth stages except maturity. Excessive rainfall (>l00 mm/week) and deficient rainfall <20 mm/week) during every stage were inadequate. Rainfall atleast 30.56 mm/week was most adequate.

Rainfall distribution over Bangladesh stations during the monsoon months in the absence of depressions and cyclonic storms

Monsoonal rainfall plays an important role in the annual rainfall distribution over Bangladesh. It is generally believed that monsoon depressions and cyclonic storms significantly affect the rainfall distribution over Bangladesh during the monsoon months and their absence causes deficient rainfall during the individual monsoon months. This aspect has been examined by computing the average rainfall for 32 meteorological observatories of Bangladesh Meteorological Department during the period 1948.91 for those monsoon months which were free from depressions and cyclonic storms. It has been found that the absence of monsoon depressions and cyclonic storms is not the main factor which causes deficient rainfall and consequent drought conditions in the individual monsoon months over different stations of the country. All the stations in the country experienced normal rainfall conditions inspite of the absence of depressions and cyclonic storms in the monsoon season (June-September).

Water requirement and water use efficiency of Sorghum and its irrigation planning under limited water resources in arid and semi arid regions of India

Water requirement and water use efficiency of sorghum was studied at Akola, Parbhani, Rahuri and Coimbatore. The study enables to understand the consumptive water demand of sorghum and water use efficiency in relation to yield. The results can be used for efficient management of both rainfall and limited water resources available for sorghum production. Seasonal Evapotranspiration (ET) losses were studied for non- irrigated kharif sorghum at Akola and Parbhani and for Rahuri and Coimbatore seasonal ET losses were studied for rabi sorghum for well distributed normal and deficit rainfall years. In the normal rainfall years ET losses were more compared to deficit rainfall years. However, water use efficiency was found higher during deficit rainfall years than normal rainfall years. The seasonal ET- yield relationship was found positively correlated but insignificant for Akola, Parbhani, Rahuri and significant for Coimbatore (5% level). At Akola and Parbhani optimum yields were observed for seasonal ET of around 486 mm and 470 mm respectively. At Coimbatore maximum yield was observed for seasonal ET of 416 mm whereas at Rahuri yield was maximum when ET loss was about 475 mm. Water Use Efficiency (WUE) ranged from 6.3 to 12.2 mm for kharif season and 5.5 to 10.1 mm for rabi sorghum. Crop coefficient Kc was found negligible during early growth stages and reached peak during flowering stage and declined subsequently during maturity to harvesting stage. The study revealed that during deficit rainfall years life saving irrigation need to be applied for all stations under consideration. If limited irrigation is available irrigations at vegetative stage (25-35 days after sowing) and at boot- flowering stage (55-65 days after sowing) be given. The boot stage is found to be the most critical stage and if only one irrigation is available, it may be given at this stage. Water stress at this stage is found to cause reduction in yield by 35 to 40%.