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: : Standarized Precipitation Index : :

Evaluation Method for the Panama Meteorological Drought

Generally, the meteorological methods dedicated to the drought analyses, have as main objective to determine, through precipitation, the event occurrence below its normal values, which represent that region. To be more accurate the Drought Indexes are established. They are based in an statistical information analysis that allows the identification of drought events, their intensity, duration, frequency and geographical distribution.

International Drought Evaluation
In the World scope, there have been developed several systems for the monitoring of drought, with different detail levels. They emphasize, by their national character and with real time systems the Drought Monitor (USA), NOAA Drought Information Center (USA) and Drought Watch (Canada).

A nivel más global, existen el Drought Monitoring Centre (Africa) y el North American Drought Monitor, implemented by various institutions from Canada, USA and Mexico in 2002(Muñoz & Núñez, 2004).

Drought Indexes

In the most used indexes for drought evaluation we can find:

  1. Palmer's Drought Severity Index (ISSP):

    Is one of the first indexes developed in America, that considers the water supply and demand in a hydric balance equation, besides, it count with the precipitation deficit. There are a few limitations in Panama, because ir requires variable data that we usually don't have it available, such as soil humidity and temperature data.

  2. Standardized Precipitation Index (SPI):

    It was developed by Mckee and colaborators in 1993. It's an index based in the precipitation probability for any scale of time, and that's why is only dependant of precipitation hystoric series. That makes it possible to identify the drought impacts in short, medium, and large periods of time. (McKee et al. 1995).

    The values obtained by the SPI represent the current hydric condition versus the historic series. It's classified in categories, according to the following table:

    SPI Range Category
    >2,00 Extremely humid (XH)
    1,50 a 1,99 Very humid
    1,00 a 1,49 Mildly humid (MH)
    0,00 a 0,99 Lightly humid (LH)
    0,00 a -0,99 Lightly dry (LS)
    -1,00 y -1,49 Mildly dry (MS)
    -1,50 y -1,99 Very dry (YS)
    <= a-2,00 Extremely dry (XS)

    Source: Doesken, Nolan; Tom McKee y Juan Kleist. Weather Center. United States, 1993

  3. Normal Precipitation Percentage:

    Basic index for rain analyses, indicates, in percent if the occured precipitation in the studied period is higher or lower to the normal precipitation.

Drought index used in Panama

In Panama, the first tries for the calculation of a drought index were developed by the Hydrometeorology Management in ETESA, that currently, as a member of the National Committee for the Fight against Drought and Desertification (CONALSED), were generated for the initiative of the project "Construction of Drought Indicators and Desertification"
To define the behavior of the precipitation in the dry and degraded areas in Panama the SPI (Standardized Precipitation Index) was used, which was very useful for the definition of the climate vulnerabilities areas.

National Maps for the Standardized Precipitation Index (SPI)

According to the goals proposed by the National Action Plan (PAN), that focuses in the environment protection in the priority territories and emphasizes in the coastal Dry Arc, the Veraguas central savanna, the Ngobe Bugle Native Reserve and the Highlands of Chiriqui, Cerro Punta Corregimiento, was developed the statistics for the Standardized Precipitation Index, using the precipitation data from the Hydrometeorology Management Meteorological Stations, located inside or near the critical areas.

With this statistical information the SPI National Maps were developed, for the scales of time of 1, 3 and 6 past months and finishing in the past day of the last month, that in these maps is June 2008. The drought or humidity categories are based in the table from the SPI definition.

Watch de Maps:

Standardized Precipitation Index - 3 months Standardized Precipitation Index - 6 months Standardized Precipitation Index - 12 months
Standardized Precipitation Index - 3 months Standardized Precipitation Index - 6 months Standardized Precipitation Index - 12 months
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