Severe flooding in Nigeria
August-October 2022
In October, flooding in Nigeria's south submerged homes and farmland, and displaced hundreds of thousands of people.
21 February 2023
13 December 2022
By Marco Petracca, Luca Ciabatta, David Fairbairn, Wolfgang Wagner, Florian Roth, Mariette Vreugdenhil, Sebastian Hahn, Luca Brocca, Nicoletta Roberto, Alexander Toniazzo and Silvia Puca (all H SAF)
Severe flooding often affects Nigeria in the rainy season, which generally spans April to October.
The rainy season in Nigeria was especially harsh in 2022, with heavy rains producing deadly, destructive floods in numerous states impacted by the worst flood in a decade.
In a period from June to late August 2022, flooding had already affected populations in several states including Lagos, Anambra, Federal Capital Territory, Borno, Ebonyi, River State, Bauchi and Benue.
During September, heavy rain, rising rivers and dam releases worsened an already dire flood situation in Nigeria.
In October, flooding in the country’s south submerged homes and farmland, and displaced hundreds of thousands of people. After prolonged and intense rains, widespread flooding affected 27 out of the 36 Nigerian states, inundating houses and streets. Transport was affected for at least two weeks, and food and fuel supplies blocked. More than 500 casualties were reported.
The deeper soil moisture layers are affected during sustained wet periods, contributing to flooding. A plot of the H SAF root-zone soil wetness index anomaly (expressed as a percentage of saturation) for layer 3 (28-100cm depth) for 30 September is shown in Figure 1.
It is based on the comparison of the near-real-time soil moisture product (RZSM-ASCAT-NRT-10 H26) with the climatological September mean from the data record and extension (RZSM-DR2019-10(H141)/RZSM-DR-EXT-10km(H142), 1992-2021). Extremely wet conditions (>20% above the mean) are present over many parts of Nigeria, also confirmed by surface soil moisture deviations for September 2022 for the ASCAT Surface Soil Moisture Data Record v7 at 12.5km spatial sampling (ASCAT SSM CDR V7 12.5KM (DATA RECORDS H119)/ASCAT SSM CDR V7 EXT 12.5 KM (DATA RECORDS H120), 2007-2021) product shown in Figure 2.
Daily precipitation estimated by H SAF near real time accumulated precipitation product P-AC-SEVIRI-PMW (H61B) was analysed in the period August, September and October for the years 2021 and 2022. The results, in terms of average monthly differences, are shown in the Figure 3.
In accordance with the anomaly in the root zone, there is a significant increase in cumulative rainfall particularly evident in northern Nigeria, with total maximum values exceeding 800mm in the same quarter of the previous year.
The increase in rainfall occurred over the Niger River Basin is confirmed also by H SAF soil moisture to rain product P-AC-SM2RAIN (H64). The analysis highlighted for October, monthly rainfall amounts larger than 150% of the average, also over the upstream section of the basin, as shown in Figure 4.
The exceptional rainfall amounts along with the soil wetter conditions created the flood event that caused several fatalities.
The percentage variation of accumulated precipitation, estimated by two different precipitation products in the period between August-October 2022, compared to the same period of the year 2021, are also shown in Figure 5.
Comparison of H SAF products
Figure 5: Percentage variation of accumulated precipitation in the quarter August-October 2022 in respect to the previous year, for both H SAF products: near real time accumulated precipitation product and soil moisture to rain product
Figure 5 confirms the analysis and highlights the good agreement between the two different, independent H SAF precipitation and soil moisture products.
The total area affected by flooding and detected by Sentinel-1(Figure 6) during October 2022 is estimated to be 4,377 km².
Figure 6 is a flood composite image derived by TU Wien, based on Sentinel-1 flood maps (TU Wien algorithm) as produced by the Global Flood Monitoring component of the Copernicus Emergency Management Service. The background image is a Sentinel-2 composite image (Sentinel-2 cloudless 2021 by EOX IT Services GmbH licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License).
Additional content
@NASAEarth imagery compares river flooding in Oct 24 2021 and Oct 11 2022 (WMO/Twitter).
NiMET (Nigeria met service) forecast from October 11, already announcing risk of floods (NiMEt/Twitter)
NiMet impact-based forecast of the 12 October (NiMET/Twitter)
GloFAS Global Flood Monitoring (GFM) (Copernicus Emergency Management Service)
