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Visualizing trends in 1981-2015 rainfall in Nigeria

  • Special Report
  • Nigeria
  • June 1, 2016
Visualizing trends in 1981-2015 rainfall in Nigeria

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  • Key Messages
  • Key Messages
    • In 2014, FEWS NET/USGS released a quasi-global (50°S–50°N, 180°E–180°W), 0.05° resolution, 1981 to near-present gridded precipitation time series: the Climate Hazards Group InfraRed Precipitation with Stations (CHIRPS) data archive. This dataset uses satellite-collected inputs in combination with rainfall gauge data to interpolate rainfall over the coverage area described above every five days. This rainfall time series reflects an improvement over past gridded precipitation time series because its precipitation estimates have been unbiased with an improved historical time series, the Climate Hazards Precipitation Climatology (CHPClim).

    • Using the CHIRPS rainfall dataset, FEWS NET/USGS staff from the EROS Center in Sioux Falls, SD and the University of California, Santa Barbara, explored trends in rainfall over Nigeria during the 1981-2015 period. This report presents a series of maps that illustrate various aspects of this analysis.

    • Overall, this analysis suggests little change in rainfall patterns over the last 35 years, outside of northern areas. More specifically, the data suggests the following:

      • No significant change in the timing of the start of season.
      • No significant change in the timing of the end of season except in the north where the season now ends 0.5 – 1.5 dekads1 later than in the 1980s.
      • No significant change in the overall length of the season, except in the north where the later end of season and a marginally earlier start of season have lengthened the season by 0.5 – 2.0 dekads.
      • Total rainfall has increased by more than 50mm across much of the country, and by more than 100mm in the north, since the 1980s. A moderate drying trend is indicated in parts of the central and southern regions.
      • In percentage terms these changes in rainfall are small (<10 percent) in most areas. Exceptions include the north, where total May-October rainfall has increased by more than 30 percent since the 1980s, and localized areas of the west where rainfall has increased by 10-15 percent.
    • Available research is insufficient to link the trends identified in this analysis with anthropogenic climate change.

    • While the CHIRPS dataset represents an improvement in satellite derived rainfall time series, this analysis would be strengthened by the inclusion of additional historical rain gauge data.

    This map combines the trend in start of season timing (Map 2) and the trend in end of season timing (Map 3) to estimate trends in the length of season. In general, the analysis suggests little change in the duration of the season outside of the north where, due to a later end date and a marginally earlier start of season, the season has lengthened by 0.5 – 2.0 dekads. This is equivalent to a lengthening of the current season by 5 to 20 days compared to the 1980s.

    Figures 1981-2015 trend in length of season (change in dekads since the 1980s)

    Figure 1

    1981-2015 trend in length of season (change in dekads since the 1980s)

    Source: FEWS NET/USGS CHIRPS

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