Extreme Events Extreme events are defined as most

Extreme Events • Extreme events are defined as “most unusual” climatic events at a given place (natural and anthropogenic causes) • “Most unusual” can be categorized as occurring less than 10 percent of the times based on historical observations • Climatic events: – – Flooding Droughts/heat waves Tropical cyclones Severe local storms (tornado, hail, wildfires, crop freeze, winter storms, straight-line wind damage, etc. ) • Can cause severe socio-economic and environmental damage

What is flood? • Excess water caused by heavy rains and/or rapid snowmelt • Usually happens on a flat or low-lying areas when the ground is saturated and water cannot run off quickly or not at all • Types: areal, riverine, estuarine and coastal, urban, catastrophic Look at some pictures from: https: //en. wikipedia. org/wiki/Flood

Magnitude-Frequency Analysis for Flood • Direct observations of stream flow can be used for magnitudefrequency analysis • Frequency of floods are useful information in designing water resources infrastructures. For example, a flood of 5 to 10 yr. frequency (or return period) is used in the design of highway culvers for low traffic. Similarly: – – Culverts (high-traffic): 50 -100 yrs. RP Highway bridge: 10 -100 yrs. RP Dam: 50 -100 yrs. RP Urban drainage: 2 -25 yrs. (small cities) and 25 -50 yrs. (large cities)

Flood Frequency Analysis Best fit line (normally fitted using Log-Pearson Type III Distribution) 1. What is the magnitude of flood that has a return period of 50 -years? 2. What is the frequency of a flood with a magnitude of 45, 000 cfs?

DDF: Depth Duration Frequency curves Generated from http: //hdsc. nws. noaa. gov for Greensboro, North Carolina What is the precipitation depth for a 12 -hr. duration storm that is exceeded on average once in in 25 years (return period = 25 years)?

IDF: Intensity Duration Frequency curves Generated from http: //hdsc. nws. noaa. gov for Greensboro, North Carolina What is the intensity of precipitation of 12 -hr. duration that has a 25 -year return period?

What is drought? Deficiency of rain (low to none) for an extended period of time Look at some pictures from: https: //en. wikipedia. org/wiki/Drought

Drought Characteristics • Droughts are among the most costly weather-related events in terms of economics and loss of life • Key aspects of drought: severity, duration, time of occurrence and spatial extent • Defined in a different number of ways: – Meteorological drought: Deficit in precipitation; It represents degree of dryness compared to the average condition and duration of the dry period – Agricultural drought: Deficit in soil moisture; It precedes precipitation deficit (meteorological drought); Reduce agricultural production due to lack of water for irrigation; Increase wildfires – Hydrological drought: Deficit in surface and ground water; Impacts water supply for drinking water, irrigation, industrial needs, hydropower, etc. ; Significant societal impact