How is the standardized precipitation index calculated?

How is the standardized precipitation index calculated?

The computation of SPI involves transformation of precipitation data into lognormal values followed by computation of U statistics, shape and scale parameters of the gamma distribution. The resulting parameters are then used to find the incomplete gamma cumulative probability of an observed precipitation event.

How is the standard precipitation index used?

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?

The Standardized Precipitation Index (SPI) is a widely used index to characterize meteorological drought on a range of timescales. Alternative indices that deal with evapotranspiration have been proposed (see SPEI).

How is SPI calculated for drought?

The SPI is calculated from the historical precipitation record at a weather station, where precipitation accumulation over a period of time is compared to that same period of time throughout the historical record at that location.

How do you calculate aridity index?

The Aridity Index (AI) is a simple but convenient numerical indicator of aridity based on long-term climatic water deficits and is calculated as the ratio P/PET. The AI is a widely used measure of dryness of the climate at a given location.

What is Schedule Performance Index in project management?

The schedule performance index (SPI) is a measure of the conformance of actual progress (earned value) to the planned progress: SPI = EV / PV. When CPI or SPI are greater than 1.0, this indicates better-than-planned project performance, while CPI or SPI less than 1.0 indicates poorer-than-planned project performance.

How do you calculate schedule performance index?

The schedule performance index (SPI) is a measure of the conformance of actual progress (earned value) to the planned progress: SPI = EV / PV.

What is SPI drought index?

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 do I calculate SPI in Excel?

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 Budyko curve?

Budyko Curve describes the theoretical energy and water limits on the catchment water balance (P-ET=Q). Budyko Curve provides a “business as usual” reference condition for the water balance.

What is moisture index?

That portion of total precipitation used to satisfy plant (vegetation) needs. The moisture index replaced Thornthwaite’s previously used (1931) precipitation-effectiveness index. Compare Palmer Drought Severity Index. Thornthwaite, C. W.

What does a CPI of 1.5 mean?

If the ratio has a value higher than 1 then it indicates the project is performing well against the budget. A CPI of 1 means that the project is performing on budget. A CPI of less than 1 means that the project is over budget.

What kind of gamma is used for precipitation index?

The analyses shown here are based on the Pearson Type III distribution (i.e., 3-parameter gamma) as suggested by Guttman (1999). The associated cumulative probability distribution is then estimated and subsequently transformed to a normal distribution.

How is the standardized precipitation index related to climate?

Climate Data. Standardized Precipitation Index (SPI) The Standardized Precipitation Index (SPI) is a widely used index to characterize meteorological drought on a range of timescales. On short timescales, the SPI is closely related to soil moisture, while at longer timescales, the SPI can be related to groundwater and reservoir storage.

How to find the SPI value of precipitation?

The transformed precipitation data are then used to compute the dimensionless SPI value, defined as the standardized anomaly of the precipitation:

What does SPI stand for in climate category?

p* = mean precipitation. σ p = 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.