Our planet’s water circulates continuously from the atmosphere to land and oceans, and back again in a process known as the hydrological cycle. The hydrological cycle includes rainfall, percolation of water into the ground, and evaporation of water from oceans, among other processes. In this entire cycle, rainfall is our only source of fresh water. It is the primary source that sustains all secondary sources like rivers and groundwater.
Rainfall is measured in millimetres. Any place has an “average annual rainfall” that is taken as a reference based on the rainfall it has actually received over a long period of time (for eg: IMD uses average annual rainfall over 50 years, from 1951 to 2000). However, each place can receive significantly different rainfall in different years. The same place may have flood years and drought years, i.e., when rainfall is a certain percentage higher and lower than the normal levels respectively.
India gets annual rainfall of 1187 mm on average, but there are huge variations within the country. Mawsynram in Meghalaya, gets annual average rainfall of 11,873 mm, about 10 times the national average. This tiny hamlet currently holds the Guinness World Record for the highest average annual rainfall on the planet. On the other extreme is Jaisalmer, the district that gets the least average annual rainfall – 186.26 mm. Around 3500 rain gauge stations of the Indian Meteorological Department (IMD) collects rainfall data regularly. Overall, northwest India gets the least annual rainfall, while northeast states get the most.
Rainfall patterns for Bangalore over 100 years, from 1901 to 2000, show that annual rainfall has varied from as low as 500 mm to as high as 1350 mm, while the city’s average rainfall is 970 mm. If we look at rainfall for Bangalore region for the month of August alone, from 1951 to 2007, the variation is even wider. The lowest rainfall was 24.3 mm (1984), and the highest was over ten times this – 247.3 mm (1998). It is wise to understand rainfall and its changing patterns, being prepared to deal with its impacts, and adapting our lives in response to it.
In Bangalore, rainfall peaks during the pre-monsoon in May, and later in September-October. While the pre-monsoon season has short spells of intense rains, monsoons bring longer spells of recurring rains. In the past, there was more opportunity for water to percolate into the natural ground in the city. However, with the paving of urban lands, surfaces become harder to penetrate and percolation has reduced because of the roads and buildings that cover large our city. Most rain water is now lost as runoff, carried away by stormwater drains.
You can measure the rainfall in own your premises by installing rain gauges, either automatic or manual. In Bangalore, manual rain gauges are supplied by vendors like Lawrence & Mayo, and automated ones by vendors like Yuktix. Real time data on rainfall is also measured by the state government’s Natural Disaster Monitoring Centre (KSNDMC), and is available here. Further data, like rainfall and forecast maps, and districtwise reports, are available here. KSNDMC has 86 weather stations in Bangalore urban taluk now. The centre gives detailed rainfall reports to NGOs, students, researchers etc., free of cost. Here is an example of rainfall analysis that was done using data accessed from KSNDMC.
Vidyaranyapura, a locality in North Bengaluru, is surrounded by multiple lakes, but as the area got urbanised, the lakes dried up. However, the groundwater table in many areas is very high, as close as 5ft from the ground level, and digging an open well in one’s property has long been a norm. Many households in… Continue reading Rainwater harvesting In Vidyaranyapura
Waterworks – The Bengaluru story from biometrust
SJR Verity, an apartment complex with 334 units and 1000 residents, required 180 KLD (kilolitres per day) of water, mostly supplied by 40 tankers of 6000 L capacity each, costing Rs 2,80,000 monthly. The MC (management committee), embarked on a 3-year-long mission to research and implement sustainable long-term solutions for the water demand. Today, after… Continue reading WATER MANAGEMENT AT SJR VERITY
Sai Poorna Paradise, situated in Bengaluru’s HSR Layout, is an apartment complex surrounded by the picturesque Begur, Somasandra, and Agara lakes. Established in 2008, the complex consists of two blocks, A and B, housing a total of 88 flats and a thriving community of 192 residents. Due to the absence of a Cauvery water connection,… Continue reading Water Management at Sai Poorna Paradise Apartments
In 2021, Biome implemented a groundwater recharge project at the Association for People with Disability (APD) campus spread across a 5-acre property on Doddagubbi Road, Kothanur. The goal was to increase borewell yield by digging enough recharge wells and providing for storage tanks to harvest rainwater, thus reducing dependence and the total annual spend of Rs 4… Continue reading Rainwater Harvesting & Groundwater Recharge Project at APD, Bengaluru
Introduction The Rail Wheel Factory (RWF), is a unit of Indian Railways, established in 1984. It manufactures and supplies 95% of the wheels, axles and wheel sets required by Indian Railways. It is located in Yelahanka (13.10849, 77.5868) on a 191 acre campus. It is categorized as a ‘red’ industry by Karnataka State Pollution Control… Continue reading Rail Wheel Factory, Yelahanka