Research ArticleCLIMATOLOGY

Past and future rainfall in the Horn of Africa

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Science Advances  09 Oct 2015:
Vol. 1, no. 9, e1500682
DOI: 10.1126/sciadv.1500682
  • Fig. 1 Temperature and aridity proxy data from marine core site P178-15 in the Gulf of Aden.

    (A) Location of site P178-15 and annual average precipitation in the eastern Horn of Africa region [GPCC (Global Precipitation Climatology Centre) v6 product (39)]. (B) TEX86-inferred SSTs (in degrees Celsius) for the past two millennia from the box core (in red) and piston core (in orange) at site P178-15. Darker error bars denote the 1σ analytical error, and lighter error bars denote the 1σ calibration error using the BAYSPAR-NRS calibration model (10). Black triangles denote intervals where the cores were dated with either 14C or 210Pb. The red star indicates modern mean annual SSTs near the core site (40). (C) δDwax data for the past two millennia from the Gulf of Aden cores, overlaid with a reconstruction of Northern Hemisphere (NH) temperatures (41). Error bars denote the 1σ analytical error. More negative (positive) values indicate wetter (drier) conditions.

  • Fig. 2 δ13C of leaf waxes (δ13Cwax) in the Gulf of Aden core for the past ca. 900 years (in green) versus the change in atmospheric CO2 δ13C (42).

    Note that although the absolute values are different, the relative scales are equivalent. The recent decrease in δ13Cwax resembles the record of atmospheric CO2 δ13C both in timing and in magnitude, indicating that δ13Cwax records the Suess effect.

  • Fig. 3 Trends in 20th century observed versus 21st century simulated precipitation in the eastern Horn of Africa region.

    (A) Trends (percent per year) in observed precipitation across the 20th century [1901–2010; GPCC v6 product (39)], including the annual mean, the two major rainy seasons (March–May and September–November), and the dry season (June–August). Stippling indicates that the trend is significant at P < 0.05 (Mann-Kendall test). (B) Multimodel mean (model n = 23) of trends (percent per year) in simulated precipitation in the CMIP5 RCP 8.5 scenario for the 21st century (2006–2099). Panels as in (A). Stippling indicates areas where at least 90% of the models agree on the sign of change.

  • Fig. 4 Simulated 21st century changes (from the RCP 8.5 scenario) in mean annual 700 mbar vertical velocity and skin temperature in the tropics and their relation to Horn of Africa rainfall.

    (A) Multimodel mean of the correlation between eastern Horn of Africa rainfall (average across 0–12°N and 40–55°E) and 700 mbar vertical velocity (colors) and the trend in 700 mbar vertical velocity (contours). Red contours indicate a positive trend; blue contours, a negative trend. Stippling indicates areas where 90% of the models agree on the sign of the trend. (B) Multimodel mean of the trend in skin temperature (Ts, effectively SST) over the tropical oceans.

  • Fig. 5 Comparison between the observed and the simulated annual cycle in precipitation in the eastern Horn of Africa (average across 0–12°N and 40–55°E).

    (A) Observed annual cycle in precipitation, GPCC v6 (39). Black line denotes the median values; gray bars denote the 90% confidence interval. (B) Simulated annual cycle in precipitation, from the CMIP5 historical experiments. Black line denotes the multimodel mean; individual colored lines represent each model.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/1/9/e1500682/DC1

    Materials and Methods

    Table S1. 210Pb dates on core P178-15 BC1.

    Table S2. Radiocarbon dates on core P178-15 BC1.

    Table S3. Radiocarbon dates on core P178-15P.

    Table S4. List of the CMIP5 models used for the analyses.

    Fig. S1. 210Pb data from P178-15 BC1.

    Fig. S2. The age model for P178-15 BC1.

    Fig. S3. The age model for P178-15P for the last 4000 years.

    Fig. S4. A sample GC-FID chromatogram of fatty acids (as methyl esters) from core P178-15P.

    Fig. S5. TEX86-based SST anomalies from P178-15 BC1 versus instrumental observations.

    Fig. S6. First derivative of the δDwax data from the Gulf of Aden.

    Fig. S7. Multimodel mean of trends in simulated precipitation from the CMIP5 historical experiment.

    Fig. S8. Projected change (%) in eastern Horn of Africa precipitation versus projected changes in zonal surface temperature gradients in the Indian and Pacific Ocean basins.

    Fig. S9. Scatterplot of the correlation coefficient between the simulated annual cycle of precipitation in the Horn of Africa versus the observed annual cycle (from GPCC v6) and the SD of a modified Dipole Mode Index (DMIm).

    Fig. S10. Scatterplot of the SD of a modified Dipole Mode Index (DMIm) and the projected change in precipitation for the RCP 8.5 experiment.

    References (4374)

  • Supplementary Materials

    This PDF file includes:

    • Materials and Methods
    • Table S1. 210Pb dates on core P178-15 BC1.
    • Table S2. Radiocarbon dates on core P178-15 BC1.
    • Table S3. Radiocarbon dates on core P178-15P.
    • Table S4. List of the CMIP5 models used for the analyses.
    • Fig. S1. 210Pb data from P178-15 BC1.
    • Fig. S2. The age model for P178-15 BC1.
    • Fig. S3. The age model for P178-15P for the last 4000 years.
    • Fig. S4. A sample GC-FID chromatogram of fatty acids (as methyl esters) from core P178-15P.
    • Fig. S5. TEX86-based SST anomalies from P178-15 BC1 versus instrumental observations.
    • Fig. S6. First derivative of the δDwax data from the Gulf of Aden.
    • Fig. S7. Multimodel mean of trends in simulated precipitation from the CMIP5 historical experiment.
    • Fig. S8. Projected change (%) in eastern Horn of Africa precipitation versus projected changes in zonal surface temperature gradients in the Indian and Pacific Ocean basins.
    • Fig. S9. Scatterplot of the correlation coefficient between the simulated annual cycle of precipitation in the Horn of Africa versus the observed annual cycle (from GPCC v6) and the SD of a modified Dipole Mode Index (DMIm).
    • Fig. S10. Scatterplot of the SD of a modified Dipole Mode Index (DMIm) and the projected change in precipitation for the RCP 8.5 experiment.
    • References (43–74)

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