Adjustment of the Standardized Precipitation Index (SPI) for the Evaluation of Drought in the Arroyo Pechelín Basin, Colombia, under Zero Monthly Precipitation Conditions

Luis José Cerpa Reyes,Humberto Ávila Rangel,Luis Carlos Sandoval Herazo

doi:10.3390/atmos13020236

Abstract

The evaluation of the meteorological drought is fundamental for the management of the water resource. One of the most used indices to evaluate the drought is the standardized precipitation index (SPI) due to its practicality and evaluation in a variety of time scales, however, this uses precipitation as the only variable, depending on the deviations in the precipitation values. This is important when evaluating the SPI, because in some ecosystems close to the equatorial zone, there are very warm periods with low rainfall, in which a large proportion of the data collected by the meteorological stations corresponds to zero. In this research, the SPI was calculated in the Pechelín basin located in Colombia, in which there is zero precipitation in a large proportion of the data, registering zero precipitation in the month of January and February in 67% and 70% respectively. As a result, the SPI values increased to “wet” ranges, only when the amount of data with zero precipitation exceeded half of the total data; this means that the SPI determines wrong values when it is calculated with zero-precipitation data in large proportions. Based on this finding, this study aims to modify the index by typing the distribution (using a correction factor K), finally correcting the SPI values, this correction was called SPI-C. The results indicate that the SPI-C improved the identification of drought, obtaining corresponding values that better represent the high frequency of zero precipitation existing in the study area.

Highlights

The standardized precipitation index (SPI) is frequently used for drought evaluation, the World Meteorological Organization considers the SPI as a universal drought index because of its capacity to be estimated for various reference periods adapting to the different response times of typical hydrological characteristics to precipitation [1]
Some investigations of the SPI as [2,3,4,5,6] show the practicality of the index to characterize drought events with few resources and at different time scales; this is an advantage over other methods of assessing drought
Some research [9,10,11,12,13,14] indicates the temporal versatility of the index is useful in determining the beginning and end of dry events, it allows the analysis of the impacts of droughts at different time scales, compared to other indices

Summary

Introduction

The SPI is frequently used for drought evaluation, the World Meteorological Organization considers the SPI as a universal drought index because of its capacity to be estimated for various reference periods adapting to the different response times of typical hydrological characteristics to precipitation [1]. The SPI represents the number of standard deviations that each precipitation data deviates from the historical average; considering this, when evaluating the drought in tropical areas, critical conditions are found, such as very severe dry periods in the months with low precipitation. Based on this characteristic, the SPI was evaluated in the Pechelín basin, located in Colombia, in this basin there are areas with zero monthly rainfall in a large proportion of the data, due to the large amount of data with zero rainfall, which exceeds 50% of the total precipitation data, resulting in “wet” SPI values.

Obtaining Data

Results

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F M A MJ