Download presentation
Presentation is loading. Please wait.
Published byJean Walker Modified over 9 years ago
1
Principles of Flash Flood Development: An Introduction to Hydrometeorology Anthony Phillips GEOG 490/590 Ball State University Hazards associated with flash floods First law of Quantitative Precipitation Forecasting (QPF) Atmospheric and hydrologic contributors
3
Objectives
4
What is a Flash Flood? What is the difference between a flood and a flash flood? The term flood usually refers to a hydrological event that takes place over many hours or days. Often associated with main- stem rivers and floodplains. A flash flood often occurs within 6 hours of a convective rainfall event, or when a dam or levee fails. Small streams and creeks are most susceptible.
5
What is a Flash Flood? The NWS defines a flash flood as: “Within six hours (often within one hour) of a causative event such as intense rain, dam break, or ice jam formation, one or more of the following occurs: River or stream flows out of banks and is a threat to life or property. Person or vehicle swept away by flowing water from runoff that inundates adjacent grounds. A maintained county or state road closed by high water. Six inches of fast-flowing water over a road or bridge. This includes low water crossings in a heavy rain event that is more than localized (i.e., radar and observer reports indicate flooding in nearby locations) and poses a threat to life or property. Dam break or ice jam causes dangerous out-of-bank stream flows or inundates normally dry areas creating a hazard to life or property. Any amount of water in contact with, flowing into, or causing damage to a residence or public building as a result of above ground runoff from adjacent areas. …”
6
Why Study Flash Floods? Which hazard is most deadly? Wind & hail Hurricanes Tornadoes Lightning Flash floods Flash floods are the deadliest hazard associated with con- vection worldwide. Flash floods cause more fatalities than tornadoes, wind, and hail combined!
7
Severe Weather Trends Decrease in tornado- and hurricane-related deaths over the past 50 years. Better preparedness Better technology Increase in lead-times However, fatalities from flash floods have not steadily decreased Interaction of meteorology with hydrology Flash flood risk is increasing Extreme (>2”) precipitation events Urbanization Population growth
8
Meteorological Factors The development of flash floods depends on several factors, a few include: Storm type and precipitation Antecedent precipitation Drainage basin size Land use characteristics Soil composition We’ll begin by reviewing the meteorological factors that can lead to the development of flash floods
9
First law of QPF
10
Maximum precipitation usually occurs only with intense or long duration convective systems Single- or multi-cell convection MCCs or MCSs Squall lines Supercells Stratiform precipitation is often too light, but can result in riverine flooding Long duration (D)
11
First law of QPF Maximum precipitation usually occurs only with intense or long duration convective systems ( Usually, rainfall duration (D) increases with decreasing storm translation speeds Mean wind speed decrease MCSs: maximum precipitation occurs when cell motion is opposed by propagation of new cells Results in quasi-stationary system motion
Similar presentations
© 2024 SlidePlayer.com. Inc.
All rights reserved.