1. Introduction Climate encapsulates the description of how the atmosphere behaves over a long period of time, informing us on the “average of weather”, as well as the description of other aspects of weather patterns and parameters distribution, including anomalous, rare and extreme weather events. Some examples of extreme events include, but are not limited to, heat waves, cold waves, floods, heavy precipitations, drought, tornadoes, and tropical cyclones. Even though extreme events do not occur often, they can be harmful to our heath, can cause great devastation to infrastructure, can affect our economy, and can even cause the loss of life (IPCC 2013, WHO reports, U.S. National Climate Assessment). It is therefore necessary for Meteorological communities to improve the understanding and characterization of extreme weather and climate events in time
locationsseem more proper to represent the disaster-causing potential, and at least three days are required to satisfy preliminary duration. For regional scales, transient event identification approach (Ren et al. 2013) is used to trace multi-day processes moving from location to location; quasi-stationary identification scheme (Chen and Zhai 2013) is used to guarantee stationary front related persistent heavy precipitation, whose major amount pours into a highly concentrated area. The latter one tends to trigger severe floods during a few days. a general framework for defining heavy precipitation is proposed. Recommendation for standard characterization of heavy precipitation To quantitatively reflect a heavy precipitation event, the definition of heavy precipitation should be complemented by characterization with the following 4 metrics: Magnitude: it is computed based on an index or a set of indices measuring the precipitation total on various time scales to measure the intensity of the event. Duration:it is computed by the number of isolated or consecutive time unitthe precipitation satisfying the extreme criteria. Severity: is a measure which integrates two aspects of the event. Its magnitude and its persistence. Extent:describes the area impacted by the heavy precipitation event.
Quantitative description: Precipitation index: Pi Threshold (Ps) Temporal information Spatial information Total precipitation 1mm in 24-hr Record at station level information on the starting time, ending time and duration of wet spell. Keep the information in a database. As a wet spell evolves with time it is important to use preferably a GIS to: 1. Calculate the area affected by the wet spell 2. Locate the coordinates of the impact stations and the center with the peak values of the characterizations: Magnitude Duration Extent Percent of total precipitation during the spell compared to the seasonal average. Computed at station level which is a number of consecutive days satisfying the threshold. The geographical area computed based on multi-station data with gridding when observing networks are dense. Another option is to use remote sensing and model analysis. Severity: Is on duration. It should be categorized in three levels: minor, long, and very long. Additional information can be provided in terms of maximum daily total recorded during the spell.
Quantitative description: Drought index: Di Threshold (Ds) Temporal information Spatial information Di: Computed using monthly or longer timescale precipitation totals, or in combination with other variables such as evaporation, temperature and relative humidity. Computed on historical values of the index. It should provide a beyond which, values are statistically rare(*), or a certain threshold value having potential negative impacts on one or several application sectors. (*) The WMO Climatological Standard normal should be used to the extent possible to define the base periods and departure from the average and percentiles. Persistent for timescales longer than a season. Record at station level information on the starting time, ending time and duration of drought. Keep the information in a database. As a drought evolves with time it is important to use preferably a GIS to: 1. Calculate the area affected by the and at which magnitude or severity. Event characterizations: Magnitude Duration Extent of Di-Ds; or defined by a synthesized method. Computed at station level which is the number consecutive months, seasons, or yearssatisfying the criteria. The geographical area computed on multi-station data with gridding when observing networks are dense. Another option is to use remote sensing precipitation data when only precipitation data is considered.
Quantitative description: Precipitation index: Pi Threshold (Ps) Temporal information Spatial information Total precipitation in 24 hours. Pi <1mm Record at station level information on the starting time, ending time and duration of wet spell. Keep the information in a database. As a dry spell evolves with time it is important to use preferably a GIS to: 1. Calculate the area affected by the wet spell 2. Locate the coordinates of the impact stations and the center with the peak values of the index characterizations: Magnitude Duration Extent Percent of total number of days with precipitation < 1 mm compared to the average length of the season. Dry periods, such as during dry seasons in arid or semi-arid areas should not be accounted. Note: the definition of the wet/dry season is defined by each country, where the start and end of the season should also be defined based on average conditions. Computed at station level which is a number of consecutive days satisfying the threshold. The geographical area computed based on multi-station data with gridding when observing networks are dense. Another option is to use remote sensing and model analysis. Severity: Is based on duration. It should be categorized in three levels: minor, long, and verylong.