# A Probabilistic Analysis of Drought Areal Extent Using SPEI-Based Severity-Area-Frequency Curves and Reanalysis Data

^{1}

^{2}

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Methodology

^{−1}and $a$ is given by a third-order polynomial in the heat index $I$.This latter is given by Equation (2), and it has for each year 12 monthly means of daily averaged temperature values as input (Equation (2))

## 3. Study Area and Data

^{2}. The climate of the island is semiarid, with a mean annual precipitation of around 700 mm and high intra-annual variability from year to year. The climatic features frequently promote the onset of drought conditions, especially during the hottest months [40,41], and these conditions are projected to become more severe in the future [33,42]. Precipitation and temperature data, used for SPEI calculation, are retrieved from the reanalysis project ERA5-Land (https://cds.climate.copernicus.eu/cdsapp#!/dataset/reanalysis-era5-land-monthly-means?tab=overview (accessed on 29 August 2023)). The data are provided as averages on a monthly scale from 1950 to the present (almost 73 years) and with a horizontal resolution of 0.1° × 0.1°.

## 4. Results and Discussion

## 5. Conclusions

## Author Contributions

## Funding

## Data Availability Statement

## Conflicts of Interest

## References

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**Figure 1.**Scheme illustrating the proposed approach for probabilistically characterizing the spatial extent of drought and deriving SAF curves based on SPEI.

**Figure 3.**Spatial averaged SPEI values from 1950 to the present considering the 12-month aggregation time scale.

**Figure 4.**Severity-Area curves referred to three different years where dry, normal and wet conditions occurred.

**Figure 5.**Probability plot of the observed ${A}_{d,t}\left({z}_{0}\right)$ vs. the corresponding quantiles computed using the derived distributions.

**Figure 6.**SAF curves and observed Severity-Area curves for three experienced events in terms of drought conditions.

**Table 1.**Categories of dryness/wetness conditions according to SPEI [30].

Categories | SPEI Values |
---|---|

Extremely drought | Less than −2 |

Severe drought | −1.99 to −1.50 |

Moderately drought | −1.49 to −1.00 |

Near normal | −0.99 to 0.99 |

Moderately wet | 1.00 to 1.49 |

Severely wet | 1.50 to 1.99 |

Extremely wet | More than 2.00 |

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**MDPI and ACS Style**

Palazzolo, N.; Peres, D.J.; Bonaccorso, B.; Cancelliere, A.
A Probabilistic Analysis of Drought Areal Extent Using SPEI-Based Severity-Area-Frequency Curves and Reanalysis Data. *Water* **2023**, *15*, 3141.
https://doi.org/10.3390/w15173141

**AMA Style**

Palazzolo N, Peres DJ, Bonaccorso B, Cancelliere A.
A Probabilistic Analysis of Drought Areal Extent Using SPEI-Based Severity-Area-Frequency Curves and Reanalysis Data. *Water*. 2023; 15(17):3141.
https://doi.org/10.3390/w15173141

**Chicago/Turabian Style**

Palazzolo, Nunziarita, David J. Peres, Brunella Bonaccorso, and Antonino Cancelliere.
2023. "A Probabilistic Analysis of Drought Areal Extent Using SPEI-Based Severity-Area-Frequency Curves and Reanalysis Data" *Water* 15, no. 17: 3141.
https://doi.org/10.3390/w15173141