STUDIES OF RADIO REFRACTIVE INDEX IN ASSOCIATION WITH ONSET OF MONSOON

Variations of radio refractive index (RRI) in the lower troposphere over Bombay and Thiru-vananthapuram have been studied for the months from April to July for the years 1979 to 1987. It is seen that in most of the years, the radio refractive index at 900 hPa over Bombay increased significantly prior to onset of monsoon over Kerala (Thiruvananthapuram) and well in advance of the arrival monsoon over Bom-bay. Variation of RRI at 850 hPa level over Bombay also shows significant increase a few days later than at 900 liPa level. At higher levels no such significant changes are observed. The KM value over Thinivanantha-purain at 900 hPa or at 850 hPa does not show significant rise from pre-monsoon to monsoon months. The results show a slight decreasing trend during the same period.

Monsoon onset and reservoir build up- A case Study for Hirakud

Onset of monsoon for each year of the period from 1961 to 1986 over the Upper Mahanadi basin has been studied taking into consideration the sharp increase in water levels of the Hirakud reservoir. This study has shown that .there are positive and negative time-lags in the arrival of monsoon run off into the reservoir. It has been seen that positive time lags are due to antecedent condition of the basin before the onset of monsoon while negative time-lag appears to be due to pre-monsoon thunderstorm activity which causes reservoir levels to increase before the onset of monsoon. Attempt has been made to discuss all these cases briefly. It has been seen that on a majority of occasions monsoon runoff has reached the reservoir with a time-lag of 1 to 4 days.

Agricultural drought monitoring and management at sub district level in Telangana

The weather or climate is considered as an important natural resource and basic input for better planning of crop and cropping system in agriculture particularly rainfed environments. Every plant process, related with growth, development and yield of a crop and each of in-season and off-season farm operations depends on weather. Amongst the various weather elements, temperatures, radiation and rainfall play crucial role in deciding the crop growth, development and yield levels. Precipitation is one of the important weather factors being responsible for atmospheric and soil moisture and therefore has more agricultural importance, especially in rainfed agriculture. Rainfed crops like jowar, maize, groundnut, greengram, blackgram and sunflower and one water-intensive crop like rice are mainly affected owing to drought. The drought conditions occur due to failure of South West Monsoon, delay in arrival of SW monsoon, and break monsoon conditions or early cessation of SW monsoon. Rainfed agriculture in India depends on onset of monsoon and the rainfall distribution during crop growth season. The amount of rainfall and the time of onset of monsoon decides the type of the crop to be grown. The timely onset and well distribution of monsoon rain in the month of June and July decides the area coverage of rainfed crops. Any deviation in the onset and distribution of southwest monsoon rainfall causes huge impact on agriculture and its dependent activities. Close monitoring of progress of monsoon and distribution of rainfall and its impact on sowing of rainfed crops is essential at sub district level to suggest time to time crop management strategies thereby to minimize the impact of aberrant seasonal conditions. In this paper a monitoring of drought at national, state and sub district (Mandal) level using indices like MAI, WRSI etc. were presented. Management strategies to reduce the impact of drought like optimum time of sowing, strategic irrigation, crop calendar, contingency crop planning etc. were discussed. Agromet advisories for communication of real time weather information for benefit of farming community were presented.

The onset and advance of Indian summer monsoon in relation with the sea level pressure field

The dates of onset of monsoon over Kerala and the advance of monsoon exhibit large interannual and intra seasonal variability. The genesis of Indian summer monsoon is considered to be in the southern hemisphere, over the Mascarene Island. The pressure gradient between the high pressure over Mascarene Island and low pressure over North West India is the fundamental physical cause of the monsoon, which acts as a driving force for the monsoon winds. Thus, the genesis of monsoon and its further advance is closely related to the sea level pressure field. With this backdrop, the variability of the onset and advance of the monsoon in terms of sea level pressure field is examined in this study. The pentad sea level pressure field does show contrast for the years of early and late onset of monsoon over Kerala and also for the years of rapid and sluggish advance of monsoon.

Effect of date of sowing and rainfall on sustainability of yield and rainwater use efficiency in cereal crops under arid alfisols

An assessment of the effects of date of sowing and crop seasonal rainfall on the sustainability of yield and rainwater use efficiency (RWUE) of sorghum, pearl millet and foxtail millet sown on five dates at 15 days interval from first fortnight of June to first fortnight of August during 2009 to 2014 under arid Alfisols at Anantapur has been made in this paper. A suitable date of sowing has been identified for each crop based on the relationships sorghum equivalent yield with crop seasonal rainfall and crop growing period observed in the 6-year study. The yield was significantly influenced by the variation in the crop seasonal rainfall and crop growing period when sown on different dates of sowing. It was significantly higher when crops were sown with the onset of monsoon in the first fortnight of June, and decreased with the subsequent sowings. Among crops, sorghum attained maximum mean yield of 923 kg ha-1 with RWUE of 2.73 kg ha-1 mm-1; while pearl millet attained mean yield of 873 kg ha-1 with RWUE of 2.95 kg ha-1 mm-1 and foxtail millet attained mean yield of 646 kg ha-1 with RWUE of 1.64 kg ha-1 mm-1 when sown during first fortnight of June. Based on the ranks assigned to the yield attained on different dates of sowing in different years, pearl millet was superior for sustaining maximum yield and RWUE comparedto sorghum and foxtail millet under arid Alfisols at Anantapur.

Taluka Wise Study of Rainfall Pattern in Nanded District of Marthwada Region (Maharashtra) Using Rainfall Data

About 60 per cent of the total cultivable area of the country is rainfed. However, prolonged dry periods affect the final crop production. Monsoon is an important season for water supplies, from surface reservoir. Uneven distribution of rainfall, affect the agricultural production remarkably. The daily rainfall data was collected for each taluka of Nanded district for the period of 20 years (1998-2017) and it was to be summed up on meteorological weekly, monthly, seasonally, annual basis for each taluka of Nanded district basis for the study of rainfall characterization. The results indicated that weekly mean annual basis total rainfall was ranged between 720.0 mm in Deglur and 1009.9 mm in Mahur. The weekly highest rainfall on annual basis was recorded in Himayat Nagar (53.7 mm) in the 30th MW amongst all the taluka considering monsoon period (23 to 42 MW). The monthly mean rainfall indicated that the lowest and highest monthly mean rainfall amongst all the taluka was observed in Nanded, Kandhar, Loha, Hadgaon, Bhokar, Kinwat, Mahur, Dharmabad, Ardhapur, Naigaon talukas (0.0 mm) in the December month and in the Mahur taluka (283.1 mm) in July month. The seasonal distribution of Nanded district was obtained in winter season (6.1 mm), in summer (15.5 mm), in monsoon (578.3 mm), in post monsoon (216.6 mm). The annual rainfall data is statistical analyzed for Nanded district and within the year and taluka to taluka ranged C.V. (%) were between 25.0 to 46.9 %. The data of taluka-wise annual normal of weather parameter (i.e. rainfall and rainy days) calculated. Here, the results indicated that the onset of monsoon was observed in 23th MW and withdrawal in 43rd MW in Nanded district. It showed that average rainfall of Nanded district is 816.4 mm with 45.0 rainy days per year. The results clearly indicated the onset of monsoon in 23th MW and withdrawal of monsoon in 43rd MW for the Nanded district should be considered. The statistical analysis for rainfall variability was worked out and it was intra-annual as well as intra-taluka variation in Nanded district. It was ranged between 19.0 to 51.0 per cent with annual mean 45.0 rainy days per year.

Extended Range Forecast of Monsoon at Smaller Spatial Domains over India for Application in Agriculture

The performance of operational extended range forecast (ERF) issued by IMD is evaluated for the southwest monsoon 2020. The early onset of monsoon over the Bay of Bengal and the normal onset of monsoon over Kerala with slightly rapid progress northward are very well captured in the ERF with two to three weeks lead time. The ERF also captured very well the transitions from normal to weaker phase of monsoon in July, the active phase of monsoon in entire August was well anticipated in ERF with a lead time of 3 weeks. The active monsoon condition in the second half of September associated with delayed withdrawal from northwest India was also reasonably well captured in the ERF. Quantitatively, the ERF shows significant skill up to three weeks on all India levels. The spatial distribution of met-subdivision level mean forecast skill of predicting above normal, normal and below normal categories in terms of correct (forecast and observed category matching) and partially correct (forecast and observed category out by one category) for the 36 subdivisions during the entire monsoon season of 2020 is found to be 89%, 83%, 80% and 78% for week 1 to week 4 forecasts respectively. The wrong forecasts (forecast and observed category out by two categories) are found to be between 11% in week 1 to 22% in week 4 forecast. Thus, the met-subdivision level forecast shows useful skill and is being used operationally for agrometeorological advisory services of IMD.