The SPI calculation for any location is based on the long-term precipitation record for a desired period. This long-term record is fitted to a probability distribution, which is then transformed into a normal distribution so that the mean SPI for the location and desired period is zero (Edwards and McKee, 1997).
What is shown by the standardized indices?
This map shows the Standardized Precipitation Index (SPI) for multiple monthly accumulation periods for the globe. The Standardized Precipitation Index (SPI; McKee 1993) is the number of standard deviations that observed cumulative precipitation deviates from the climatological average.
What is precipitation concentration index?
Precipitation concentration index (PCI), defined by Oliver [44], is also a powerful indicator for temporal precipitation distribution. Similar to CI, PCI is generally used for evaluating seasonal precipitation changes to investigate the heterogeneity of monthly rainfall data.
How do you calculate the antecedent precipitation index?
The formula used to calculate API value presented by Kohler and Linsley (1951) is applied to summarize the daily precipitation amounts:(1) API = ∑ t = 1 M P t k t where, Pt is the precipitation in the tth AD; M is the statistical number of ADs; k is the decay constant.
What is antecedent precipitation index?
The Antecedent Precipitation Index (API) is a running day by day measure of catchment wetness based on the rainfall that has occurred over preceding days. The most recent rain counts more in the API than rain from previous days. High values of API mean the catchment is wet so any rain is likely to run off.
What is SPI in agriculture?
The Standard Precipitation Index (SPI) is a relatively new drought index based only on precipitation. It’s an index based on the probability of precipitation for any time scale. Some processes are rapidly affected by atmospheric behavior, such as dry land agriculture, and the relevant time scale is a month or two.
How is the standard precipitation index used?
To calculate the SPI (Standard Precipitation Index), a long-term precipitation record at the desired station is first fitted to a probability distribution (e.g. gamma distribution), which is then transformed into a normal distribution so that the mean SPI is zero (McKee et al., 1993, 1995).
What is SPI drought?
What is antecedent soil moisture?
Antecedent soil moisture is a frequently used term in surface water hydrology and refers to the water content of the upper soil layer in a catchment prior to a storm event.
What is the antecedent precipitation factor?
Antecedent precipitation is precipitation falling before, but influencing the runoff yields of, a given rainfall event. An API gives a measure of soil mois- ture index. It thus often remains a subjectively deter- mined and arbitrarily implemented parameter in rainfall–runoff modelling (Heggen, 2001).
What is the standardized precipitation index?
The Standardized Precipitation Index (SPI; McKee 1993) is the number of standard deviations that observed cumulative precipitation deviates from the climatological average. It can be calculated for any time scale; various monthly and multi-monthly time scales are shown here.
What is the SPI value in precipitation data?
The raw precipitation data are typically fitted to a gamma or a Pearson Type III distribution, and then transformed to a normal distribution. The SPI values can be interpreted as the number of standard deviations by which the observed anomaly deviates from the long-term mean.
How is observed precipitation quantified?
It quantifies observed precipitation as a standardized departure from a selected probability distribution function that models the raw precipitation data. The raw precipitation data are typically fitted to a gamma or a Pearson Type III distribution, and then transformed to a normal distribution.
How do you calculate SPI for drought?
SPI = (P-P*) / σp. where P = precipitation. p* = mean precipitation. σp = standard deviation of precipitation. The dimensionless SPI values are typically associated with the drought descriptions of “dry”, “moderately dry”, or “extremely dry”, as well as other labels for near-normal conditions or precipitation excesses.
