Sierra Leone – Meteorological Agency Faces Forecast and Warning Challenges

Gabriel Kpaka of Sierra Leone Meteorological Agency gives a meteorological perspective of the flood and landslide disaster in Regent Village, Freetown, Sierra Leone.

Freetown, Sierra Leone Aug 14, 2017. Red Cross volunteers are digging for survivors and supporting distraught families in the wake of heavy flooding and mudslides that have ripped through Sierra Leone’s capital Freetown. As many as 3,000 have been made homeless. Entire communities have been washed away and whatever is left is covered in mud. The mudslides come following three days of torrential rains. Photo credit: Sierra Leone Red Cross Society

Torrential rain in the late hours of Sunday (14/08/2107) into Monday (15/082017) resulted in hundreds of deaths and loss of properties due to mudslides and flooding in Regent, Freetown, Sierra Leone. A national emergency has been declared and the flood disaster is thought to be the worst in Africa in the past two decades according to the Sierra Leone government and international rescue agencies.

Challenges for Early Warning Systems

Despite the concern around climate change, understanding hydro-meteorological hazards still faces many challenges. Studies have shown that combining future projections of various climate variables with hydro-meteorological hazard event characteristics need to be undertaken to improve our understanding of climate change hazards.

However, flooding and landslides are rare events, which require a long-time record of both the climate and the hazardous events. But the lack of some meteorological equipment (especially radar), data gap, flood forecasting software and few trained meteorological technicians at the Sierra Leone Meteorological Agency have been the major challenge in providing early warning systems in Sierra Leone. Even if the historical record of climate data is available, the completeness of hazard inventories may be questionable and inhomogeneous.

Rainfall and Slope Stability

Furthermore, while heavy rainfall is a precursor for many flood and landslide events, the occurrence also depends on the spatial variability, antecedent precipitation and temperature, and properties of the landscape.

One of the causes of the mudslide was the decreased stability of slope material, related particularly in the case of unconsolidated sediments to a sudden change in water content.

In general, the moisture content of slopes depends mainly on climate, and in particular on weather conditions. The latter explains why landslide is discontinuous in time and space, even where conditions are favourable. Mount Sugarloaf on the edge of Regent town gave way and caused catastrophic damage. Measurement by Sierra Leone Meteorological Agency Weather station in Freetown (Wilberforce) recorded a significant rain event in the region on 14 August, 2017. Nearly 81.3 mm fell in 12 hours, of which 70 mm fell in about 7 hours.

The monthly total at this station (10.83 inches / 275.08mm) through 15 August, 2017 was over 300% above average; creating the higher likelihood for dangerous mudslides in a significant rain event due to saturated soil. The forecast on the 13th August 2017 issued by the Sierra Leone Meteorological Agency indicated a significant rainfall was possible with high rainfall probabilities over the next 24 hours period.

Forecasts and Warnings

The lack of a radar equipment is the primary challenge to forecast exact rainfall amounts. There is an urgent need for radar and forecasting software to be installed at the Meteorological forecasting studio in order to beef up the early warning systems for the country.

A query of the Sierra Leone Meteorological Agency weather station thunder and lightning network pulses detected over the last four days over Sierra Leone (Lat 7 to 9.5 and long -14 to -10) shows 167,754 pulses. Unfortunately, the query did not indicate the event was caused by thunderstorms as there was no lightning detected in the exact region of the mudslide over the four days examined.

The rainfall was from warm, tropical, low-topped convection in a supersaturated atmosphere. Probably caused by the Intertropical Convergence Zone (ITCZ) disturbance interacting with a sea breeze front that moved inland off the warm, tropical Atlantic.

Human Causes

Floods occur due to human causes as well as natural causes.  The leading causes of floods in Sierra Leone include intense precipitation, inadequate capacity within river banks to contain high flows, and silting of riverbeds. Another increasing and significant cause of flooding is deforestation.

The city of Freetown, especially the mountainous areas, has been observing increasing deforestation with residents cutting down the trees for firewood and charcoal. Deforestation plays several roles in the flooding equation because trees prevent sediment runoff, the unimpeded raindrop impact on bare ground leads to heavy erosion and quick runoff. Other factors include landslides leading to obstruction of flow and change in the river course, poor natural drainage, and heavy rainstorms.

Funding and Investment

With the increasing need for better measurements driven by the changes in our atmosphere, there is urgent need to fund the Sierra Leone Meteorological Agency with seed money to suit a broad range of issues.  These vary from the state of the art weather stations, forecasting software, training of technicians to weather radar and regional collaboration.

Gabriel Kpaka is the Deputy Director and UNFCCC Focal Point for Sierra Leone, Sierra Leone Meteorological Agency

Map of affected areas of Freetown, Sierra Leone. Image credit ECHO / EU

Flood Summary

Last updated: August 30, 2017
Event
Sierra Leone, August 2017
Date
August 14, 2017
Type
Flash flood, Landslide
Cause
Extreme rainfall, Long-term rainfall
The flooding and landslides of 14 August occurred after 80 mm of rain fell in a few hours.

The verification of registered affected persons led by Ministry of Social Welfare, Gender and Children’s Affairs took place on 26-27-28 August with support from several humanitarian partners. A total of 1,424 households were verified and/or newly registered bringing the total of directly affected people to 5,962 including 904 children under 5 years and 113 pregnant women.

Further flooding occurred 26/27 August Freetown. UN Office for the Coordination of Humanitarian Affairs reported that flooding damaged a health centre, a bridge and a school at Kroo Bay. One person was reported dead and two injured.

Locations

A - Regent
B - Freetown
C - Goderich
D - Lumley
E - Kissy Brook

Magnitude

Rainfall level
81.3 mm in 24 hours
Wilberforce, Freetown - August 14 to August 14, 2017
Nearly 81.3 mm fell in 12 hours of which 70 mm fell in about 7 hours, according to Sierra Leone Meteorological Agency

Damages

Fatalities
409 people
August 14 to August 19, 2017
According to ECHO figures
Missing people
810 people
August 14 to August 19, 2017
According to ECHO figures
Injured
330 people
August 14 to August 19, 2017

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