Radar & Observation
Radar Reflectivity (dBZ)
Radar reflectivity measures returned energy to show raindrop size and concentration. Use the storm visualization guide to translate color scales, then compare them with the 20 mm in 1 hour page to anticipate surface intensity.
Doppler Velocity
Doppler velocity shows whether raindrops move toward or away from the radar, revealing wind shear and rotation that steer heavy bands. Pair it with reflectivity in the radar guide and contrast with the live rain simulator to picture how shifting winds change on-the-ground intensity.
Runoff & Watersheds
Runoff
Runoff is rainfall that flows over land once interception and infiltration are exceeded, carrying pollutants toward streams. The water harvesting guide shows how capture reduces runoff, while the 25 mm in 30 min scenario illustrates how bursty rain accelerates overland flow.
Hydrograph
A hydrograph plots streamflow versus time, highlighting the rising limb, peak, and recession after a storm. Use it to compare how detention ponds delay peaks—start with the Learning Path sequence and match shapes to simulator runs at different intensities.
Watershed / Catchment
A watershed (catchment) is the land area draining to a shared outlet, controlling how quickly rainfall becomes runoff. Smaller basins respond faster, while larger ones spread the hydrograph. The Learning Path and 10 mm in 1 hour page help estimate timing for different basin sizes.
Infiltration Capacity
Infiltration capacity is the maximum rate soils can absorb water before runoff forms. Permeable, dry ground starts high but drops as pores fill; compacted soils begin lower. Compare gentle rain in the intensity guide with simulator presets to see when soil intake is exceeded.
Detention and Retention
Detention basins temporarily store runoff and release it slowly, while retention basins keep water until it infiltrates or evaporates. Both are sized from design storms and IDF targets—revisit the storage guide and test ideas with the 20 mm intensity page.
Stormwater Infrastructure
Stormwater infrastructure covers pipes, swales, green roofs, and permeable pavements that convey or treat runoff. Performance depends on rainfall intensity and duration—stress-test layouts with our rain simulator and the extreme intensity reference page.
Design & Planning
Return Period
A return period expresses the average interval between events of a given magnitude, such as a 1% annual chance for a 100-year storm. It guides design thresholds—review the intensity categories guide and an example like 50 mm in 1 hour to visualize what rare storms can resemble.
Intensity-Duration-Frequency (IDF) Curves
IDF curves link rainfall intensity to duration for specific return periods, forming the backbone of design storms. They translate climate statistics into actionable numbers—pair them with the rainfall units guide and Learning Path steps to keep units consistent.
Related Resources
Authoritative Sources
International Organizations:
- • World Meteorological Organization (WMO)
- • International Association of Meteorology
- • Global Precipitation Measurement (GPM) Mission