India receives 80 per cent of its annual rainfall during the southwest monsoon season of June to September. Rainfall over the country during this season shows a wide range of spatial variation due to orographic influences and preferential occurrence of rain-bearing systems in certain regions. India has a very extensive raingauge network and rainfall monitoring over the country is a stupendous task.
monitoring and statistical analysis of districtwise daily rainfall is
one of the important functions of the Hydrometeorological Division of
IMD at New Delhi. Based on the real time daily rainfall data, weekly
districtwise, sub-divisionwise and statewise rainfall distribution
summaries are prepared regularly by the Rainfall Monitoring Unit. Maps
showing weekly and cumulative rainfall figures in 36 meteorological
subdivisions of the country are prepared. This information is very
important to many user agencies, particularly for agricultural planning.
A World Bank-aided Hydrology Project covering a 6-year period is presently under implementation in IMD. This project aims at enhancing the physical infrastructure of hydrometeorological activities and data processing and management systems resulting in an enhancement of rainfall data quantity and quality. Eight southern states and five central agencies including IMD, are involved in the project. IMD has an important and active role of providing technical guidance to concerned states/central agencies in procurement and installation of standardised equipments, inspection of existing and new raingauge stations, and imparting specialised training to personnel at various levels in the states/agencies.
IMD renders assistance and advice on the meteorological aspects of hydrology, water management and multipurpose river valley projects management. These services are utilised by the Central Water Commission, Ministry of Agriculture, Ministry of Water Resources, Railways, Damodar Valley Corporation Flood Control Authorities and the State Governments. The following special units of the Hydrometeorology Division cater to the needs of specific interests:
Storm Analysis Unit:
Provides design estimates of short duration rainfall in different sub-zones of the country for the purpose of railway and road bridge construction. Hydrometeorological data for a number of river catchments are analysed for computing probable maximum storms, return periods of very heavy rainfall and run-off relationships.
Flood Meteorological Unit:Flood Meteorological Offices (FMOs) have been set up by IMD at ten locations viz., Agra, Ahmedabad, Asansol, Bhubaneshwar, Guwahati, Hyderabad, Jalpaiguri, Lucknow, New Delhi and Patna. During the flood season, FMOs provide valuable meteorological support to the Central Water Commission for issuing flood warnings in respect of the following rivers:
Agra Lower Yamuna and Betwa
Design Storm Unit:
Design storm studies are being conducted to study rainfall magnitude and its time distribution for use as main input for the design engineers in estimation of flood for hydraulic structures, irrigation projects, dams etc. on various rivers. The probable maximum precipitation values are also evaluated for optimum utilisation of water resources. The generalised one day point PMP maps for different states of India have been published.Water Balance Unit:
Water balance studies are being conducted in respect of river basins by applying the well-known techniques of Thornthwaite for water budgeting and mass conservation principles.Glaciology Unit:
To conduct glaciological studies, information on meteorological parameters and snow accumulation in the upper watersheds of the Himalayan rivers is being collected by ground observations, remote sensing techniques and participation in glaciological expeditions. For a better possible observational network 27 snowgauges/raingauges (17 in Himachal Pradesh and 10 in Uttar Pradesh) have been installed in the western sector of the Himalayas under the Glaciology Scheme.