An Analysis of Precipitation Extreme Events Based on the SPI and EDI Values in the Free State Province, South Africa
Abstract
:1. Introduction
2. Materials and Methods
2.1. Study Area
2.2. Materials
2.3. Methods
2.3.1. Standardized Precipitation Index
2.3.2. Effective Drought Index
2.3.3. Extreme Value and Return Level Analyses
2.3.4. Extreme Frequency Analysis (EFA)
3. Results
3.1. Historical Analysis
3.2. Trend Analysis
3.3. Extreme Value Analysis
3.4. Return Level Analysis
3.4.1. Return Level Analysis for Drought Conditions
3.4.2. Return Level Analysis for Wet Conditions
3.5. Dry Return Periods Based on Extreme Frequency Analysis (EFA) in the Free State Province
3.6. Wet Return Periods Based on Extreme Frequency Analysis (EFA) in the Free State Province
3.7. Frequency Distribution of Precipitation and the Drought Indices
4. Discussion and Conclusions
- (a)
- Whilst the return levels for the drought/wet duration and severity of EDI and SPI-3, -6 and -12 values generally showed increasing patterns across the corresponding return periods, the spatial contrasts were only noticeable in the return levels derived from the wet/drought duration and severity derived from SPI-3, -6, and -12 values (and not from the EDI values).
- (b)
- The EFA results point to a noticeable spatial contrast in the return periods derived from the EDI and SPI-3, -6, and -12 values for each of the extreme precipitation categories: moderately wet, severely wet, extremely wet to moderately, and severely dry.
- (c)
- Over the four decades, the Free State Province has generally experienced a suite of extreme precipitation categories ranging from moderately wet, severely wet, extremely wet to moderately dry, severely dry, and extremely dry conditions.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
References
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Category | Range of Drought Index Values | |
---|---|---|
SPI | EDI | |
Extremely dry | −2.0 | −2.0 |
Severely dry | From −1.5 to −1.99 | From −1.5 to −1.99 |
Moderately dry | From −1.0 to −1.49 | From 1.0 to −1.49 |
Normal | From −0.99 to 0.99 | From −0.99 to 0.99 |
Moderately wet | From 1.0 to 1.49 | From 1.0 to 1.49 |
Severely wet | From 1.5 to 1.99 | From 1.5 to 1.99 |
Extremely wet | 2.0 | 2.0 |
Effective Drought Index | |||||
DISTRICT | 2 Year Period | 5 Year Period | 10 Year Period | 20 Year Period | 50 Year Period |
60 | 4.08 | 4.72 | 4.87 | 4.94 | 4.98 |
61 | 4.08 | 4.72 | 4.87 | 4.94 | 4.98 |
70 | 2 | 2 | 2 | 2 | 2 |
71 | 3 | 3 | 3 | 3 | 3 |
72 | 3.40 | 4.78 | 5.69 | 6.56 | 7.69 |
73 | 2 | 2 | 2 | 2 | 2 |
81 | 2 | 2 | 2 | 2 | 2 |
82 | 3 | 3 | 3 | 3 | 3 |
83 | 5.64 | 6.59 | 6.82 | 6.92 | 6.97 |
Standardized Precipitation Index (3) | |||||
60 | 2 | 2 | 2.01 | 2.12 | 5.53 |
61 | 2 | 2 | 2 | 2 | 2 |
70 | 3.58 | 3.90 | 3.96 | 3.98 | 4 |
71 | 3.26 | 4.50 | 5.44 | 6.44 | 7.90 |
72 | 2 | 2 | 2 | 2 | 2.23 |
73 | 2.80 | 3.40 | 3.72 | 3.98 | 4.27 |
81 | 4.01 | 4.69 | 4.85 | 4.93 | 4.97 |
82 | 3 | 3 | 3 | 3 | 3 |
83 | 3 | 3 | 3 | 3 | 3 |
Standardized Precipitation Index (6) | |||||
60 | 2 | 2 | 2 | 2 | 2 |
61 | 2 | 2 | 2 | 2 | 2.23 |
70 | 5.17 | 5.85 | 5.95 | 5.98 | 6 |
71 | 3 | 3 | 3 | 3 | 3 |
72 | 2 | 2 | 2 | 2 | 2 |
73 | 2 | 2 | 2 | 2 | 2 |
81 | 3.86 | 5.78 | 7.26 | 8.86 | 11.23 |
82 | 3.89 | 5.66 | 7.89 | 11.45 | 19.73 |
83 | 3.89 | 5.66 | 7.89 | 11.45 | 19.73 |
Standardized Precipitation Index (12) | |||||
60 | 2 | 2 | 2 | 2 | 2 |
61 | 3.02 | 3.55 | 3.80 | 3.99 | 4.17 |
70 | 2 | 2 | 2 | 2 | 2 |
71 | 3.44 | 4.82 | 5.78 | 6.44 | 7.90 |
72 | 2.89 | 3.91 | 4.70 | 5.56 | 6.82 |
73 | 2 | 2 | 2 | 2 | 2 |
81 | 2 | 2 | 2 | 2 | 2 |
82 | 3.56 | 6.03 | 8.61 | 12.17 | 19.11 |
83 | 4.82 | 5.67 | 5.86 | 5.94 | 5.98 |
Effective Drought Index | |||||
DISTRICT | 2-Year | 5-Year | 10-Year | 20-Year | 50-Year |
60 | 2.66 | 2.89 | 2.95 | 2.98 | 2.99 |
61 | 2.66 | 2.89 | 2.95 | 2.98 | 2.99 |
70 | 2 | 2 | 2 | 2 | 2 |
71 | 2.66 | 2.89 | 2.95 | 2.98 | 2.99 |
72 | 2.98 | 3.99 | 4.75 | 5.55 | 6.72 |
73 | 2.99 | 3 | 3 | 3 | 3 |
81 | 2 | 2 | 2 | 2 | 2 |
82 | 2.55 | 2.85 | 2.93 | 2.97 | 2.99 |
83 | 3.02 | 3.55 | 3.80 | 3.99 | 4.17 |
Standardized Precipitation Index (3) | |||||
60 | 2 | 2 | 2 | 2 | 2 |
61 | 3.65 | 3.95 | 3.99 | 4 | 4 |
70 | 2 | 2 | 2.07 | 4.42 | 5.25 |
71 | 3.02 | 3.55 | 3.80 | 3.99 | 4.17 |
72 | 2 | 2 | 2 | 2 | 2 |
73 | 3.07 | 3.63 | 3.87 | 4.02 | 4.16 |
81 | 3.02 | 3.55 | 3.80 | 3.99 | 4.17 |
82 | 2.80 | 3.40 | 3.72 | 3.98 | 4.27 |
83 | 3.54 | 3.93 | 3.98 | 3.99 | 4 |
Standardized Precipitation Index (6) | |||||
60 | 3.02 | 3.55 | 3.80 | 3.99 | 4.17 |
61 | 2.66 | 2.89 | 2.95 | 2.98 | 2.99 |
70 | 2 | 2 | 2 | 2 | 2 |
71 | 3.43 | 3.82 | 3.91 | 3.96 | 3.98 |
72 | 2 | 2 | 2 | 2 | 2 |
73 | 2.98 | 3.99 | 4.75 | 5.55 | 6.72 |
81 | 2 | 2 | 2 | 2 | 2 |
82 | 3.02 | 3.55 | 3.80 | 3.99 | 4.17 |
83 | 3.02 | 3.55 | 3.80 | 3.99 | 4.17 |
Standardized Precipitation Index (12) | |||||
60 | 2.80 | 3.40 | 3.72 | 3.98 | 4.27 |
61 | 2 | 2 | 2 | 2 | 2 |
70 | 2 | 2 | 2 | 2 | 2 |
71 | 2.66 | 2.89 | 2.95 | 2.98 | 2.99 |
72 | 4.11 | 4.72 | 4.87 | 4.94 | 4.98 |
73 | 2.80 | 3.40 | 3.72 | 3.98 | 4.27 |
81 | 2 | 2 | 2 | 2 | 2 |
82 | 2 | 2 | 2.07 | 4.42 | 5.15 |
83 | 3.34 | 5.17 | 6.88 | 9.03 | 12.83 |
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Adeola, O.M.; Masinde, M.; Botai, J.O.; Adeola, A.M.; Botai, C.M. An Analysis of Precipitation Extreme Events Based on the SPI and EDI Values in the Free State Province, South Africa. Water 2021, 13, 3058. https://doi.org/10.3390/w13213058
Adeola OM, Masinde M, Botai JO, Adeola AM, Botai CM. An Analysis of Precipitation Extreme Events Based on the SPI and EDI Values in the Free State Province, South Africa. Water. 2021; 13(21):3058. https://doi.org/10.3390/w13213058
Chicago/Turabian StyleAdeola, Omolola M., Muthoni Masinde, Joel O. Botai, Abiodun M. Adeola, and Christina M. Botai. 2021. "An Analysis of Precipitation Extreme Events Based on the SPI and EDI Values in the Free State Province, South Africa" Water 13, no. 21: 3058. https://doi.org/10.3390/w13213058