# Spatial and Temporal Analysis of Dry and Wet Spells in the Wadi Cheliff Basin, Algeria

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## Abstract

**:**

## 1. Introduction

## 2. Materials and Methods

#### 2.1. Study Area and Data

^{2}and lies between 00°07′44″ E and 03°31′07″ E and between 33°53′13″ N and 36°26′34″ N (Figure 1). The topography of the basin is complex and rugged. The altitude varies from −4 m to 1969 m.

#### 2.2. The Standardized Precipitation Index (SPI)

_{0}, c

_{1}, c

_{2}, d

_{1}, d

_{2}and d

_{3}are coefficients whose values are:

_{0}= 2.515517, c

_{1}= 0.802853, c

_{2}= 0.010328

_{1}= 1.432788, d

_{2}= 0.189269 d

_{3}= 0.001308

#### 2.3. Run Theory

#### 2.4. Theil–Sen Estimator

_{1}, x

_{2}, …, x

_{n}precipitation observations at times t

_{1}, t

_{2},…, t

_{n}(with t

_{1}< t

_{2}< … < t

_{n}), for each N pairs of observations x

_{j}and x

_{i}taken at times t

_{j}and t

_{i}, the gradient Q

_{k}can be calculated as:

_{j}> t

_{i}.

_{1}, x

_{2}, …, x

_{n}can then be calculated as the median Q

_{med}of the N values of Q

_{k}, ranked from the smallest to the largest:

_{med}sign reveals the trend behavior, while its value indicates the magnitude of the trend.

#### 2.5. Mann–Kendall Test

_{j}and x

_{i}are the observations taken at times j and i (with j > i), respectively, and n is the dimension of the series.

_{0}, the distribution of S is symmetrical and is normal in the limit as n becomes large, with zero mean and variance:

_{i}indicates the number of ties with extend i.

_{MK}as:

## 3. Results

## 4. Discussion

## 5. Conclusions

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Conflicts of Interest

## References

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**Figure 1.**Location of the study area and of the selected 150 rain gauges on an elevation map, along with the distribution of the average annual precipitation evaluated from the 150 rain gauges with a spline interpolation.

**Figure 2.**Example of drought characteristics evaluated using the run theory for a given threshold level [34].

**Figure 3.**Characterization through boxplots of frequency (%), average duration (in years), average severity, and average intensity (year

^{−1}). The top and the bottom of the boxes are the third and the second quartiles, respectively; the band inside the box is the median and the ends of the whiskers represent the minimum and maximum of all of the data.

**Figure 4.**Spatial distribution of the (

**a**) dry frequency in %, (

**b**) average dry duration in years, (

**c**) average dry severity and (

**d**) average dry intensity in year

^{−1}.

**Figure 5.**Spatial distribution of the (

**a**) wet frequency in %, (

**b**) average wet duration in years, (

**c**) average wet severity and (

**d**) average wet intensity in year

^{−1}.

**Figure 6.**Spatial results of the trend analysis performed on the SPI values. The trend magnitude has been evaluated with the Theil–Sen estimator; the statistical significance of the trends, with a SL = 95%, has been assessed with the Mann–Kendall test. Colored points indicate significant trends.

**Figure 7.**Spatial results of the correlation analysis computed, with the Pearson method and for each station, between the SPI values and the NAO. Large sized points reveal a significant correlation, while small points show non-significant correlations.

SPI Value | Class | Probability (%) |
---|---|---|

SPI ≥ 2.00 | Extremely wet | 2.3 |

1.50 ≤ SPI < 2.00 | Severely wet | 4.4 |

1.00 ≤ SPI < 1.50 | Moderately wet | 9.2 |

0.00 ≤ SPI < 1.00 | Mildly wet | 34.1 |

−1.00 ≤ SPI < 0.00 | Mild drought | 34.1 |

−1.50 ≤ SPI < −1.00 | Moderate drought | 9.2 |

−2.00 ≤ SPI < −1.50 | Severe drought | 4.4 |

SPI < −2.00 | Extreme drought | 2.3 |

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**MDPI and ACS Style**

Achite, M.; Krakauer, N.Y.; Wałęga, A.; Caloiero, T. Spatial and Temporal Analysis of Dry and Wet Spells in the Wadi Cheliff Basin, Algeria. *Atmosphere* **2021**, *12*, 798.
https://doi.org/10.3390/atmos12060798

**AMA Style**

Achite M, Krakauer NY, Wałęga A, Caloiero T. Spatial and Temporal Analysis of Dry and Wet Spells in the Wadi Cheliff Basin, Algeria. *Atmosphere*. 2021; 12(6):798.
https://doi.org/10.3390/atmos12060798

**Chicago/Turabian Style**

Achite, Mohammed, Nir Y. Krakauer, Andrzej Wałęga, and Tommaso Caloiero. 2021. "Spatial and Temporal Analysis of Dry and Wet Spells in the Wadi Cheliff Basin, Algeria" *Atmosphere* 12, no. 6: 798.
https://doi.org/10.3390/atmos12060798