How might we deploy a cost-effective solution t​​o greatly increase the spatial coverage of rainfall monitoring?​

Catchment & Waterways Department, Drainage Planning Division

Singapore experiences an average of 167 rain days in a year, including 31 to 73 days classified as heavy rain days (based on 10 years of data). 

Today, PUB is relying on 81 units of rain gauges across 710 km2 of land area to monitor rainfall across the entire island. Due to World Meteorological Organization’s requirements as well as limited suitable sites for installing rain gauges, there will be locations where rain gauges are sited as far as 3-5km away from each other. This results in the problem whereby the nearest rain gauges are too far to give representative readings of the rain intensity in certain areas. 

Due to the convective nature of Singapore’s weather system, the rainfall in Singapore can vary significantly spatially and temporally. It is important that PUB obtains adequate rainfall data to support decisions to deploy flood management resources. The ex​isting density of the rain gauge network does not provide enough resolution of the rainfall distribution and therefore, there have been instances in which the nearest rain gauge does not capture the actual rainfall at​​ a location at a particular moment because it is sited outside the localised heavy rain area.

●  The sensors must be appropriately sized (in terms of dimensions and weight) to be retrofitted to the top of public infrastructure such as lamp posts, bus stops, moving buses or HDB flats. Their weight shall not exceed the allowable designed loading on top of the infrastructure and in accordance with LTA or other relevant government requirements.
●  Each installation shall be approved by a professional engineer (Civil) with endorsed structural calculations as well as relevant government agencies.
●  The sensors must be self-powered and can be recharged using solar or renewable sources.
●  The sensor should ideally require minimal maintenance. The accuracy or functionality of the sensor must be minimally impacted when subjected to outdoor conditions, for example, falling leaves, bird droppings, extreme heat due to the sun, lightning.
●  The transmission of rainfall data must be done in real-time at 5-minute intervals from the onset of rain.
●  When drift in data accuracy is observed, rectification works should be carried out within 6 hours.
●  The sensors need to measure precipitation (mm) and transmit the data wirelessly in real time.
●  Proposed method statements for the calibration and preventive/corrective maintenance to ensure continuous operation of the sensor​s and the accuracy of the sensors, shall be provided. The method statements shall take into account safety considerations to access the sensors and to carry out the work.
●  The rainfall measurements provided by the sensor or proposed technology should be bench-marked with rain gauges for accuracy. This should be tested and verified according to a sound scientific methodology or certified by relevant Qualified Person.
●  The rainfall measurements provided by the sensor or proposed technology shall minimally achieve within +/- 15% of rainfall measurements provided by rain gauges

Existing Rain Gauge
●  Have stringent installation requirements which limits the number of suitable sites. 

Use of AI/machine learning to estimate rainfall intensity from CCTV images
●  Already being explored by PUB to provide rainfall intensity estimation.
●  The number of CCTVs is limited, and it is not cost effective to install new CCTVs solely for the purpose of estimating rainfall intensity
 ●  Technology has limited applications in the evening/at night due to poor lighting conditions of the CCTV images​ ​

After selection
●  PUB will provide the preferred locations for deploying the sensors. Solution provider is to obtain all necessary agencie​s approval for the installa​tion and maintenance of the sensors.
●  Data from rain gauges for validation and calibration purposes.

Total project period: less than 12 months
Solution development and deployment: up to 6 months
Solution testing and da​ta analysis: up to 6 months

An integrated system of cost-effective rain sensors that is validated through deployment and testing in a district in Singapore. The sensors should be mounted on appropriate public infrastructure such as lamp posts, bus stops, HDB flats, moving buses or any other suitable structures that the solution provider can propose. A dashboard interface developed by the solution provider shall provide a system overview and data visualisation of all deployed sensors in one dashboard. All sensors to be provided for this pilot including the customised web page for display of data shall be owned, operated and maintained by the solution provider. The solution provider will be responsible for obtaining the necessary approval from the relevant agencies. 

If the pilot is successful, the solution will be provided to PUB through a leasing model to which the solution provider is to provide an indicative pricing model.