Articles (32)
Case Study · 27 min read
5,513 reservoirs: fewer dry monsoons above India's dams
We traced the catchment of every reservoir in India's national water database and compared its rain in 1979–93 and 2009–23. Most catchments got a little wetter, with fewer dry monsoons and fewer dry years in a row. The exception is the east, where reservoirs in Jharkhand, Bihar and Uttar Pradesh now see about twice as many dry monsoons.
Case Study · 25 min read
Is the rain above India's hydropower plants changing?
We traced the catchment above each river-fed powerhouse in the national register and compared 45 years of rain over them. Heavy rain has not risen overall. Instead the map has shifted: wetter Western Ghats and peninsula, drier springs in the western Himalaya, fewer heavy days in the Northeast.
Technology · 10 min read
Which elevation model: SRTM, Copernicus, CartoDEM, lidar
SRTM, Copernicus DEM, ASTER, CartoDEM and airborne lidar compared: what each one measures, how accurate it is, and which task each suits.
Technology · 9 min read
Reservoir inflow forecasting for dam operation
How operators estimate the water about to enter a reservoir, which methods they use, and why the forecast matters as much as the level.
Technology · 6 min read
Reservoir evaporation and the water balance
How much water a reservoir loses to the air, how that loss is estimated, and why it is the hardest term in the water balance to pin down.
Technology · 8 min read
India's flood forecasting network: how CWC stations work
How the Central Water Commission's forecasting stations collect data, issue level and inflow forecasts, and pass warnings to districts.
Technology · 9 min read
Flash Flood Guidance Systems (FFGS) explained
How a flash flood guidance system turns rainfall estimates and soil moisture into a threat map, how South Asia's version works, and where ground data still matters.
Technology · 9 min read
How flood risk is assessed: hazard, exposure, vulnerability
Flood risk is not the same as a flood: it combines how likely and how deep the water is, what lies in its path, and how badly it is harmed.
Technology · 9 min read
What a '100-year flood' really means
A 100-year flood is a flood with a 1 in 100 chance of being equalled or exceeded in any year, and this article shows how that number is estimated and why it is uncertain.
Technology · 9 min read
Flood hazard maps in India and floodplain zoning
How a flood hazard map is made, what the flood zones mean, and why zoning law has been slow to reach the floodplain.
Technology · 9 min read
Backwater and tides: when river level stops meaning flow
What the backwater effect is, why a stage-discharge rating fails when the downstream end of a river moves, and how hydrologists measure flow in those conditions.
Technology · 9 min read
Data assimilation in flood forecasting, simply explained
How forecasters keep a river model honest by blending it with the latest gauge readings, from simple error correction to the ensemble Kalman filter.
Technology · 13 min read
AI flood forecasting: what ML can and cannot do
How machine-learning flood models work, where they beat conventional models, and where a forecaster should still be careful.
Technology · 6 min read
Rate-of-rise alerts: why the speed of a rise matters
A river level of 2 m can be harmless or urgent. How fast the level is climbing often tells you which, and how to turn that into a usable alert.
Technology · 9 min read
Alarm fatigue: tuning thresholds to avoid false alerts
How to set river and rainfall alert thresholds so that every alert is believed, using hysteresis, persistence, phased warnings and a plain count of false alarms.
Technology · 9 min read
What is a debris flow? Effects on river monitoring
What the term means, how a debris flow differs from a flood, and why it breaks the assumptions behind ordinary stage and discharge measurement in Himalayan streams.
Technology · 13 min read
Landslide early warning systems in India
How rainfall thresholds, ground sensors and the field signs people can see are combined into a landslide early warning system, and what India's national forecasting effort looks like.
Technology · 8 min read
Impact-based forecasting and warnings
Why a warning should say what the weather will do, not only what it will be, and how a likelihood-and-impact matrix turns a forecast into a colour and an action.
Technology · 8 min read
Ensemble forecasts: reading a probability forecast
What an ensemble forecast is, how a set of 51 runs becomes a chance of rain, and how to read spread, probability and reliability before you act.
Solutions · 8 min read
Groundwater level monitoring with telemetry
How piezometers, pressure sensors and telemetry turn a few visits a year into a continuous record of what is happening underground.
Solutions · 15 min read
How to measure canal discharge: flumes, weirs and radar
The structures, gate ratings and non-contact radar methods used to measure flow in irrigation canals, with the standard equations, worked examples and a calculator.
Solutions · 13 min read
Urban flooding in India: why cities flood
How paving a city changes the way rain becomes runoff, how Indian storm drains are sized, why they are overwhelmed, and what planners can do about it.
Technology · 6 min read
Warning level vs danger level for river gauges
What the warning level, danger level and highest flood level on a CWC river gauge mean, how they set the yellow, orange and red flood categories, and how they differ from IMD's rainfall alerts.
Technology · 14 min read
Types of hydrological models: rainfall-runoff to hydraulics
How hydrological and hydraulic models are classified, what each kind can and cannot do, how they are calibrated and scored, and why every one of them depends on good river and rainfall data.
Technology · 11 min read
Time of concentration: why small catchments flood so fast
What time of concentration is, how it differs from lag time and time to peak, how to estimate it with the Kirpich formula and the NRCS velocity method, and why it sets the design storm in the rational method.
Technology · 14 min read
Catchment area vs watershed: delineating a basin from a DEM
What catchment, watershed, river basin and command area mean, how a basin is traced from a digital elevation model step by step, and where the method goes wrong in Indian terrain.
Technology · 12 min read
Glacial lake outburst floods (GLOFs): causes and monitoring
How glacial lakes form and fail, how an outburst flood travels down a Himalayan valley, what the October 2023 South Lhonak flood showed, and how lakes are monitored.
Technology · 13 min read
The velocity-area method: how rivers are gauged by hand
How a hydrographer turns depths and point velocities across a river into one discharge figure, with a fully worked example and what changes in a monsoon flood.
Technology · 13 min read
Why Indian reservoirs lose storage: sediment and siltation explained
How rivers carry sediment into a reservoir, where it settles, how much storage Indian reservoirs lose each year, and how and how often the capacity curve should be checked.
Technology · 12 min read
How dam spillways and gates work, and why gate operations need real-time data
Spillway and gate types, the design flood, the ogee discharge equation with a worked example, and why every gate decision depends on what the river is doing upstream and downstream.
Technology · 12 min read
Data quality control for hydromet time series: spikes, gaps, flat lines and drift
The faults that creep into water-level and rainfall records, what causes them, the automatic checks that catch them, and how to flag and correct data without ever losing the original.
Technology · 13 min read
What a hydrograph tells you: reading a flood after it has passed
How the rising limb, peak, recession and baseflow of a flood hydrograph describe a catchment, how to measure lag time and separate baseflow, and why the rising limb is the part that matters for warnings.