Did the city really receive 18 cm of rainfall last Saturday? Officials concerned say not exactly. “18 cm rainfall was recorded at the rain gauge station at Narayanaguda. The rainfall recorded at Begumpet was about 7.5 cm,” said officials of the Andhra Pradesh State Disaster Mitigation Society (APSDMS), an autonomous body that maintains the rain gauge stations across the State. There are 25 such stations in the Greater Hyderabad Municipal Corporation limits.
GHMC officials, though, say that 25 are not at all adequate. “Going by international standards, the city should ideally have around 150 rain gauge stations,” said a GHMC official on condition of anonymity. As per the World Meteorological Organisation (WMO), there should be one rain gauge station for every 4 sqkm. When contacted, Sanjay Gupta, chief executive, APSDMS, said currently there are around 1200 rain gauge stations in the State and 800 more are coming up by March next year.
Coupled with what is called a Doppler Weather Radar (DWR), data from rain gauge stations can be used to make weather prediction, interpretation, analysis and also manage traffic during heavy rainfall. There are 14 DWRs in the country of which three are in the State at Machilipatnam, Hyderabad and Visakhapatnam. Each such radar costs Rs 10 crore.
On the idea that DWR can be used for better traffic management during heavy rain, Y K Reddy, Director, IMD Hyderabad, explained, “data obtained by a DWR helps in prediction of rainfall. It is the weatherman who makes the predictions on real-time basis, not the radar. If there are less rain gauges, we would not be able to assess the actual distribution of rainfall. A DWR works independently from an automated rain gauge station. But combining the data of both, proper results and forecast could be derived.” A DWR has a range of 100-150 km when it is used for forecasting rain, but otherwise in the case of cyclone detection, it can be used for up to 500km.
Echoing similar views, Ramana Murthy, Deputy Executive Engineer, APSDMS, felt a better network of rain gauge system could provide value additions like traffic and urban flood management. “DWR will help in assessing the intensity of possible rainfall and distribution.
It can estimate rainfall in a catchment or low-lying area and accordingly, warnings can be issued. If a certain amount of rain fills a lake and nalas overflow, residents in the area can be warned,” he said. Adding further, he said, “in case of the doppler data, the accuracy of real parametres like rainfall, windspeed, wind directions, temperatures, relative humidity, surface pressure could be better achieved if ground data or local data is combined with it. If more information is added, better interpretation, analysis and forecast can be derived.”
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