A New 60-Year 1940/1999 Monthly-Gridded Rainfall Data Set for Africa
Abstract
:1. Introduction
2. Materials and Methods
2.1. History of the HSM_SIEREM Database
2.1.1. The Reference Database
Constitution of the Reference Data Set
Criticism of the Reference Data Set
- the period of the rainy and dry seasons; and
- a range of monthly rainfall values (minimum and maximum) that were not to be crossed.
- exceeded the previously defined values for the country;
- was identical to the value of the same month of the previous or next year at the station; or
- was identical to the value of the previous month of the same year.
2.1.2. The Period
2.2. Geographical Processing
2.2.1. Reference of the CRU Grid Constitution
2.2.2. Choice of the Interpolation Process Options
2.2.3. Options for Spatialization
- The default power value was used: 2.
- Priority was given to the radius around the interpolated point, with a value of six times the cell size of the output grid (in this case, each cell was half a square degree; the radius is then three decimal degrees). All the points within the radius were used for the interpolation.
- A minimum of four observation points were required to spatialize. If this minimum was not filled, the radius was extended until the program found four points.
- The output grid cell size was half a square degree. This was the common resolution of the grids used for regional modeling.
- The crest line of the Atlas Mountains is known to stop the humid Atlantic winds. Therefore, a barrier-line was created along this crest line, which modified the spatialization so that the interpolation did not use the values of points that were beyond the barrier line, on both sides.
- The extent of the spatialization process was 18° west, 51.5° east, 37.5° north, and 35° south. If this option was not present, the spatialization stopped at the stations located at the four edges—west, east, north, and south.
2.2.4. Validation of the IDW Interpolation
2.2.5. Comparison between the CRU and HSM_SIEREM Grids
- A total of 4402 cells (in brown and yellow), i.e., 43%, had values ranging from −10% to −15,640%, compared to the HSM_SIEREM grid. They were mostly located in the Sahara and overlapped with the Sahel. In this area, the CRU grid had wide areas with values of mean annual rainfall between 0 and 20 mm, while the HSM_SIEREM ranged from 10 to 50 mm.
- A total of 4708 cells (in white), i.e., 45%, had values between −10% and +10%, compared to the HSM_SIEREM grid, which is very close.
- A total of 1270 cells (in green), i.e., 12%, had higher values, between +10% and +92%, compared to the HSM_SIEREM grid cells, the highest values being located on the southern slope of the Atlas Mountains (due to the barrier-line created in the HSM_SIEREM spatialization) and in Eastern Egypt (Dubief [22] drew a 5 mm isohyet in this area for the 50 first years of the 20th century).
3. Grid Production and Quality Assessment
3.1. Analysis of Rainfall Inter-Annual Variability
3.2. Statistical Tests on Mean Annual Rainfall
3.3. Monthly Time-Series
4. Discussion and Conclusion
Author Contributions
Acknowledgements
Conflicts of Interest
References
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Observed Data | Gridded Data |
---|---|
Null hypothesis rejected at confidence levels of 99%, 95%, and 90% Probability of exceeding the critical value 1.93 × 10−6 in 1979 | Null hypothesis rejected at confidence levels of 99%, 95%, and 90% Probability of exceeding the critical value 5.44 × 10−3 in 1969 |
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Dieulin, C.; Mahé, G.; Paturel, J.-E.; Ejjiyar, S.; Tramblay, Y.; Rouché, N.; EL Mansouri, B. A New 60-Year 1940/1999 Monthly-Gridded Rainfall Data Set for Africa. Water 2019, 11, 387. https://doi.org/10.3390/w11020387
Dieulin C, Mahé G, Paturel J-E, Ejjiyar S, Tramblay Y, Rouché N, EL Mansouri B. A New 60-Year 1940/1999 Monthly-Gridded Rainfall Data Set for Africa. Water. 2019; 11(2):387. https://doi.org/10.3390/w11020387
Chicago/Turabian StyleDieulin, Claudine, Gil Mahé, Jean-Emmanuel Paturel, Soundouss Ejjiyar, Yves Tramblay, Nathalie Rouché, and Bouabid EL Mansouri. 2019. "A New 60-Year 1940/1999 Monthly-Gridded Rainfall Data Set for Africa" Water 11, no. 2: 387. https://doi.org/10.3390/w11020387