Determining the start, duration, and strength of flood and drought with daily precipitation: Rationale

Abstract

[1] Determinations of the start, duration, and strength of flood and drought are important in the operational monitoring and to decision-makers, but cannot be made through the commonly-used Standardized Precipitation Index. Physical considerations are provided in this note for measuring the daily flood and drought extent with precipitation. The rationale is that, because of the memory of the soil-land surface system, the flood and drought extent of a day is contributed by the precipitation of both the day and the earlier days, while the contribution of the earlier day precipitation is decayed due to the demands of the water balance, including the runoff, evapotranspiration, and percolation. The proposed index has the same unit and magnitude as precipitation, and is easy to calculate. It can be used to evaluate the interannual variabilities and long-term changes of the start, duration, and strength of flood and drought. Citation: Lu, E. (2009), Determining the start, duration, and strength of flood and drought with daily precipitation: Rationale, Geophys.

Determining starting time and duration of extreme precipitation events based on intensity

“…2c, the most possible extreme is the 9 d precipitation event from Day 3 to Day 11. Similar to Lu (2009), our new approach here is intended to be objective, but still leaves space to be flexible. It contains a parameter, a decimal fraction, in the established relation.…”

“…The actual intensity calculated from the data can then be compared with this prescribed intensity. The method should contain, if needed, only a single parameter, which ideally is between 0 and 1, similar in style to Lu (2009), who proposed a method to monitor drought based on physical considerations and mathematical derivations. With an adjustable decimal fraction number, we may conveniently analyze the behavior of the result under various circumstances, such as when the parameter is given a moderate value (e.g.…”

“…With an adjustable decimal fraction number, we may conveniently analyze the behavior of the result under various circumstances, such as when the parameter is given a moderate value (e.g. 0.5) or tends toward the 2 special cases of being 0 and 1, as illustrated by Lu (2009).…”

A Study of the K Drought Monitoring Model

“…The above results reveal that the state from precipitation defi cit to drought-forming needs to go through a changing process that is related to soil moisture. This is the inherent decay mechanism of the soil-land surface system, which is caused by the demands of the water balance [33]. These The Construction Process of the Model Based on the above basic ideas, a simple physical drought-monitoring model is constructed and involved in the contribution of precipitation and evapotranspiration to the formation of drought.…”

“…Usually, there are two types of decay modes, i.e., exponential and the linear types. In the study by Lu [33], the exponential decay mode was considered when the infl uence of previous precipitation on drought was analyzed. Here, a comparison of the two decay modes is given in order to select the better one.…”