Q1. What is the purpose of developing and launching the "Beach Water Quality Forecast System"?
In line with the vision to develop Hong Kong into a smart city, the Environmental Protection Department (EPD) has launched a research and development project to establish water quality forecast models for Hong Kong beaches. Through the smart technology platform, we wish to transform the forecast models into a practical tool for disseminating the latest forecast results to the public.
The “Beach Water Quality Forecast System” aims to predict short-term beach water quality fluctuations arising from changes in hydrometeorological conditions, and to supplement the existing “Beach Water Quality Monitoring Programme” that relies conventionally on past monitoring data, with a view to providing comprehensive water quality information, facilitating the public in early planning of water recreation activities.
Q2. What are the differences between the existing Beach Water Quality Monitoring Programme and "Beach Water Quality Forecast System" ? Why do we need to forecast beach water quality?
The existing Beach Water Quality Monitoring Programme assesses the water quality of bathing beaches based on the measured E. coli level in the bathing waters. The collected water samples generally take time to be processed and analysed by the laboratory, and the bacterial content in the samples cannot be obtained immediately. However, scientific studies have shown that bacteriological water quality of bathing beaches could fluctuate rapidly due to changes in hydro-meteorological conditions (e.g. pollutants deposited on land could be washed off to the sea during heavy rainstorms). Although the existing conventional monitoring programme can reasonably capture the recent trend of beach water quality, it may not be able to reflect timely the latest water quality status of the beaches.
The Beach Water Quality Forecast System, on the other hand, applies statistical and data-driven modelling tools and utilizes the most relevant and the latest environmental and hydro-meteorological data as model inputs to forecast the short-term changes in beach water quality. The forecasts can supplement the existing Beach Water Quality Monitoring Programme which relies on past monitoring data, with a view to enhancing protection of the public health.
Q3. Which beaches are covered by the water quality forecast system?
The "Beach Water Quality Forecast System" will announce the daily water quality forecasts for all gazetted beaches in Hong Kong that are open for swimming. Members of the public can visit the Leisure and Cultural Services Department’s dedicated webpage for the opening arrangements of individual beaches.
Q4. What is the update frequency of the beach water quality forecasts? Can longer-term forecasts be provided?
The latest beach water quality forecasts for individual beaches are released on EPD’s beach thematic website at or before 9 AM daily. Members of the public can obtain the latest water quality forecasts for early planning of water recreation activities and journey before heading to the beach. It is challenging to project longer-term forecasts as beach water quality fluctuates rapidly with changes in weather and hydrological conditions. Therefore, at present the system only provides water quality forecasts for the current day. The public should pay attention to the last update time of the information when reviewing the water quality forecasts.
Q5. What is the operation principle of the "Beach Water Quality Forecasting System"?
The “Beach Water Quality Forecast System” is developed based on a statistical multiple linear regression model, which takes into account the most relevant and the latest environmental and hydrometeorological parameters and data, including microbiological data, rainfall, onshore wind, tide level, salinity, solar radiation and water temperature, to predict the daily E. coli level at the beaches. The forecasts are then converted into an easy-to-understand “Beach Water Quality Forecast Index”.
Q6. How accurate is the "Beach Water Quality Forecast System"? What are the limitations?
The overall accuracy of the forecast system is over 80%, slightly higher than the existing Beach Water Quality Monitoring Programme of less than 80%. In particular, the accuracy in capturing events where E. coli level exceeds 180 per 100mL is about 30-40%, significantly higher than the existing Beach Water Quality Monitoring Programme of less than 20%. The accuracy of the model is comparable to the findings of other similar studies (such as the beach water quality forecast system in California, USA). In conclusion, the forecast system can better capture the days with poor beach water quality at a lower "false positives" rates.
It should be noted that beach water quality is readily affected by various complex factors, including rapid changes in hydrometeorological conditions. It is generally impossible to accurately project all water quality changes, no matter how perfect the prediction model is. The “Beach Water Quality Forecast System” can only project short-term beach water quality fluctuations arising from changes in hydrometeorological conditions, and is unable to predict water quality deterioration caused by unknown pollution sources. Therefore, the forecast system shall be used in parallel with the existing Beach Water Quality Monitoring Programme to achieve a complementary effect and provision of comprehensive water quality information.
Q7. What is “Beach Water Quality Index”?
The "Beach Water Quality Forecast System" predicts the daily E. coli level at beaches, and the forecasts are then announced in form of "Beach Water Quality Forecast Index". To facilitate easy understanding of the forecasts, the index system is established making reference to the existing beach water quality grading system, with classifications from "1 - Good" to "4 - Very Poor". When the Beach Water Quality Forecast Index is 4, which means that there is potential transient water quality fluctuation caused by heavy rain, and the predicted water quality at this beach is "Very Poor".
Q8. What is the basis for the categories of the “Beach Water Quality Forecast Index”?
Similar to the existing beach water quality grading system, the “Beach Water Quality Forecast Index” is established making reference to the guidelines of the World Health Organization and based on the results of past epidemiological studies conducted by local scholars. The results of the studies revealed that significantly higher rate of swimming-associated illness symptom was observed with increasing E. coli levels. The “Beach Water Quality Forecast Index” assesses the risk of infection by predicting the level of E. coli in beach water.
Q9. Why E. coli is used as an indicator for beach water quality forecast?
According to local epidemiological studies, E. coli is the best indicator to reflect the risk of skin and gastrointestinal diseases caused by exposure to sewage. Predicting the level of E. coli at beaches can effectively assess the degree of feacal contamination, and possibly indicating the presence of some disease-causing microorganisms. Meanwhile, E. coli is also one of the commonly used and internationally recognized "indicator bacteria" in monitoring beach water pollution.
Q10. Why may the "Beach Water Quality Forecast Index" sometimes deviate from the current "Beach Grading"?
The "Beach Grading" generally reveals the recent trends of beach water quality. However, beach water quality may experience short-term fluctuations due to various complex factors, including rapid change in hydrometeorological conditions. During adverse weather, there may even be transient deterioration in water quality. The “Beach Water Quality Forecast System” can predict these short-term beach water quality fluctuations, hence providing additional reference information for the public. The forecasted water quality may therefore differ from the published beach grading (which is based on the past actual monitoring data).
Q11. What should I pay attention to when the "Beach Water Quality Forecast Index" shows an "Index 4"?
When the forecast index of a beach is “4-Very Poor”, which means that there is potential transient water quality fluctuation caused by heavy rain, and bathers should consider avoiding swimming at the beach.
Q12. Will the opening and closing of beaches affected by the “Beach Water Quality Forecast Index”?
In general, when the water quality forecast of an individual beach is "4 - Very Poor", the Leisure and Cultural Services Department will hoist a red flag at the beach and issue a press release to remind swimmers of the water quality forecast result.
It should be noted that the "Beach Water Quality Forecast Index" provides only the prediction on beach water quality, and is not actual monitoring data obtained from field sampling and measurements. The information should be used as reference only.
Q13. Why is there sometimes no water quality forecast information for some beaches? Why is the water quality forecast displayed as "!"?
The forecast system is designed to predict water quality fluctuations arising from changes in hydrometeorological factors. Forecasts will not be published whenever there is water quality deterioration caused by unforeseen pollution events (for example, the beach is graded as "Very Poor" under the existing Beach Water Quality Monitoring Programme, or in the event of sewage leakage incidents, etc.). The system will alert the public to possible swimming associated health risks with "!".
Q14. How can I find out more about the “Beach Water Quality Forecast System”?
Please contact us at 2838-3111 or email to enquiry@epd.gov.hk for more about the Beach Water Quality Forecast System.