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The FSR includes values for two key variables mapped across the UK: the M5-60 minutes rainfall, and the ratio "r". M5-60 minutes rainfall is the expected depth of rainfall in millimetres (mm) from a storm lasting 60 minutes (1 hour) with a return period of 5 years (hence M5).
= 4.1 R-0.21 mm −1 (equivalent to 41 R-0.21 cm −1 in the reference [4]), R being the rainrate in stratiform precipitation in millimeters per hour; D = raindrop diameter in mm The units of N 0 are sometimes simplified to cm −4 but this removes the information that this value is calculated per cubic meter of air.
Environment Canada reports a chance of precipitation (COP) that is defined as "The chance that measurable precipitation (0.2 mm of rain or 0.2 cm of snow) will fall on any random point of the forecast region during the forecast period." [7] The values are rounded to 10% increments, but are never rounded to 50%. [8]
An intensity-duration-frequency curve (IDF curve) is a mathematical function that relates the intensity of an event (e.g. rainfall) with its duration and frequency of occurrence. [1] Frequency is the inverse of the probability of occurrence. These curves are commonly used in hydrology for flood forecasting and civil engineering for urban ...
Otherwise, the factor A can be determined from a data record of rainfall and runoff using the method explained below under non-linear reservoir. With this method the reservoir can be used as a black box model. Conversions 1 mm/day corresponds to 10 m 3 /day per ha of the watershed 1 L/s per ha corresponds to 8.64 mm/day or 86.4 m 3 /day per ha
Pan evaporation is a measurement that combines or integrates the effects of several climate elements: temperature, humidity, rain fall, drought dispersion, solar radiation, and wind. Evaporation is greatest on hot, windy, dry, sunny days; and is greatly reduced when clouds block the sun and when air is cool, calm, and humid. [ 1 ]
The rainfall data can be either a user-defined time series or come from an external file. Several different popular rainfall file formats currently in use are supported, as well as a standard user-defined format. The principal input properties of rain gages include: rainfall data type (e.g., intensity, volume, or cumulative volume)
The runoff curve number (also called a curve number or simply CN) is an empirical parameter used in hydrology for predicting direct runoff or infiltration from rainfall excess. [1] The curve number method was developed by the USDA Natural Resources Conservation Service , which was formerly called the Soil Conservation Service or SCS — the ...