India's flood forecasting network: how CWC stations work

A river is rising, and a district officer asks a simple question: who is watching it, and when will we be told? In most large Indian rivers the answer is the Central Water Commission (CWC), a body under the Ministry of Jal Shakti. CWC flood forecasting rests on a network of gauging sites, telemetry, modelling centres and control rooms that has grown from a single station to several hundred. This article explains how that network is organised, how many flood forecasting stations in India CWC operates, what a forecast contains, and how it reaches the people who must act on it.

How many flood forecasting stations are there in India?

CWC's Standard Operating Procedure (SOP) for flood forecasting, issued in April 2026, states that forecasts are issued at 350 stations: 200 level forecast stations and 150 inflow forecast stations [1]. The network began in November 1958 with one station on the Yamuna at Delhi [2]. By 2008 it had 175 stations, including 28 inflow forecast stations, in 9 major basins and 71 sub-basins [2].

Two kinds of station matter here, and the difference is easy to miss:

• A level forecast station is a river site where CWC predicts the water level (stage) some hours ahead. The forecast helps district administrations decide on measures such as evacuating people and their movable property [1].
• An inflow forecast station is a dam, reservoir or barrage where CWC predicts the flow entering the structure. It helps operators release water safely and still keep storage for the post-monsoon months [1].

The sites sit in 20 river basins. The Ganga basin has the most, with 139 stations in the SOP (96 level, 43 inflow), followed by the Brahmaputra with 45 [1]. Hill states appear too. The SOP's list of level forecast sites includes Himachal Pradesh, for example Paonta Sahib on the Yamuna [1].

Forecasting stations are only part of the picture. CWC also keeps many hydrological observation stations that feed them. According to the SOP, telemetry equipment for water level and rainfall has been installed at 1,121 stations [1]. These figures change from year to year as stations are added and lists revised, so check the latest SOP or the forecasting website for the current count.

How does a CWC flood forecasting station work?

A forecasting station is a gauging site that sends data to a forecaster, and the forecaster sends back a forecast. The SOP describes the chain in five steps [1]:

1. Data collection. In the non-monsoon season gauge readings are taken three times a day and discharge once a day. In the monsoon, river levels are collected hourly, by hand and from sensors [1].
2. Transmission. Data travel by wireless, telephone or mobile, and by satellite telemetry. In the modernised network, a site sends data by satellite to one of three earth receiving stations (Burla, Jaipur and New Delhi), and from there by VSAT to the Modelling Centres. There are 27 Modelling Centres. Automated sites also use GSM or GPRS [1].
3. Data entry. Observations are entered hourly into CWC's Water Information Management System (WIMS), which performs a first validation of the values [1].
4. Formulation. Forecasters at the divisional or sub-divisional office prepare the forecast [1].
5. Dissemination. The forecast goes to local administrations and other users, and to the public forecasting website.

Telemetry stations need upkeep, and the SOP lists the duties. Staff inspect each site monthly. They clean the solar panels, the tipping-bucket rain gauge and the battery leads monthly, and also after every heavy rainfall, dust storm or flood. They also check the sensor reading against a gauge installed alongside it [1]. The upkeep list is a reminder that a forecast is only as good as the last time someone cleaned the sensor. We cover this in post-monsoon maintenance for river monitoring stations.

How are flood forecasts made?

CWC uses different methods at different scales. At divisional and sub-divisional level, short-range forecasts of 6 to 24 hours are prepared with statistical tools: correlation curves and unit hydrographs [1]. A correlation curve (gauge-to-gauge relation) links the level at an upstream site to the level that will follow downstream. A unit hydrograph gives the runoff response of a catchment to a unit of effective rainfall.

At headquarters, a rainfall-runoff model produces a 168-hour (7-day) advisory forecast. CWC says the 3-day advisory began in 2017, was extended to 5 days in 2021 and has been a 7-day advisory since 2023 [1]. The SOP describes these as advisory products for CWC offices and some disaster managers. Divisional forecasters consult them when preparing short-range forecasts, especially for stations that have no correlation graph [1]. For the models themselves, see hydrological models explained.

Worked example: a correlation forecast (illustrative)

Suppose a gauge 60 km upstream reads 8.40 m at 14:00, and a long-term correlation curve for this reach says a level of 8.40 m upstream corresponds to about 7.10 m at the forecast site, with a travel time of 7 hours.

Forecast level at the downstream site   ≈ 7.10 m, expected at 21:00
Validity of the forecast               = travel time + 1 h = 8 h  (SOP rule [1])

The SOP says that the "duration of forecast can be used as travel time + 1 hr", and that the next forecast must be issued before the previous one expires [1]. These numbers are invented to show the arithmetic. Real correlation curves are built from years of paired records.

What triggers a forecast, and what do the colours mean?

A level forecast is issued when the water level at a forecasting station touches or is expected to touch its warning level. The warning level is usually 1 m below the danger level, though it depends on the threat perception at that location [1]. For an inflow station, the trigger is a threshold inflow set for the reservoir or barrage [1]. We explain the thresholds in warning level vs danger level.

CWC's daily bulletins classify each level forecast site by its stage [1][3]:

The highest flood level (HFL) is the highest level ever recorded at the site. CWC's central control room issues special "Orange" and "Red" bulletins for severe and extreme situations, repeated every 6 hours and every 3 hours respectively [1]. The categories follow the daily bulletin's definitions [3] and the colours follow the SOP's alert categories [1].

How are forecasts delivered, and where is the CWC flood forecast portal?

Forecasts are disseminated through several channels at once: the Flood Forecasting website, e-mail, telephone, SMS, social media and the FloodWatch India app [1]. The public CWC flood forecast portal is at ffs.india-water.gov.in, and the seven-day advisory forecasts are on a separate portal, aff.india-water.gov.in, both listed in the CWC daily bulletin [3].

Behind the portal sits a control-room structure. CWC runs 36 Divisional Flood Control Rooms and a Central Flood Control Room in New Delhi [1]. The divisional rooms issue a daily flood bulletin, with water level (8:00 hours), rainfall (8:30 hours) and any forecasts, at around 11:00. The central room merges these into a national bulletin for NDMA, the Ministry of Home Affairs, the Railway Board, IMD and others [1].

Since 2022 CWC level forecasts also go out as Common Alerting Protocol (CAP) messages through an application developed by C-DOT with NDMA. They go first to the State Disaster Management Authorities, which turn them into warnings the public can understand [1]. Who owns each step is explained in who issues warnings in India, and the open-data side in open water data in India.

How accurate are CWC forecasts?

CWC judges a forecast by one criterion: a stage forecast is accurate if the level actually reached falls within ±15 cm of the forecast, and an inflow forecast if the inflow is within ±20 % [1]. In the 2008 season, 97.9 % of 5,670 level forecasts and 98.2 % of 1,021 inflow forecasts met these limits [2].

Those high percentages need care. The same appraisal report points out that a single yardstick misleads on flashy rivers. On the Ganga in Bihar, the level rarely rises by 15 cm in 24 hours even in high flood. At Rishikesh, the river can rise more than 15 cm in under 3 hours [2]. The report also notes that a forecast can be within the limit on peak level yet wrong on the time of the peak, and that time is not scored [2]. For small hill catchments, where the whole flood passes in hours, a forecast of a few hours' lead is a different problem. We discuss it in flash floods vs river floods: warning time.

What the network does not cover

The forecasting network is built around larger rivers with sites at bridges and barrages. A small stream in a hill catchment may have no CWC forecasting station at all, and its flood can arrive faster than any divisional forecast cycle. Local sensors fill that gap, sending data to the same district officers who receive CWC's alerts. Choosing and placing them is covered in how to choose a river water level sensor, and the way data move from sensor to dashboard in what is an RTDAS.

Key points

• CWC issues flood forecasts at 350 stations: 200 for river levels and 150 for reservoir inflows (SOP, April 2026) [1].
• The network began with one station at Delhi in 1958 [2].
• Short-range forecasts of 6–24 hours come from correlation curves and unit hydrographs; headquarters adds a 7-day rainfall-runoff advisory [1].
• A forecast is triggered at the warning level, usually 1 m below the danger level; bulletins classify sites as above normal (yellow), severe (orange) or extreme (red) [1][3].
• Accuracy is judged at ±15 cm for level and ±20 % for inflow, a single yardstick that treats flashy and slow rivers alike [1][2].
• Forecasts are published at ffs.india-water.gov.in and sent to state authorities as CAP alerts [1][3].

Where ClimMaTech fits

CWC's network covers the main stems and key reservoirs, and districts often need local readings upstream of a village, a bridge or a drain. At ClimMaTech we build river monitoring stations that record level, and where needed surface velocity, on board and report over GSM. Our flood warning solution links such readings to local alerts, so that officers can read them next to CWC's bulletins.

References

1. Central Water Commission, Standard Operating Procedure for Flood Forecasting, April 2026. cwc.gov.in
2. Central Water Commission, Flood Forecasting and Warning Network Performance Appraisal 2008, New Delhi, February 2010. cwc.gov.in
3. Central Water Commission, Flood Forecast Monitoring Directorate, Daily Flood Bulletin No. 13, 13 May 2024. cwc.gov.in