Disasters in Africa (Mudslides, Flooding)

Climate change has been affecting Africa disproportionately, leading to human and economic losses across the continent. Over the years, African countries have nursed these losses, with various countries struggling to catch up with the effect of climate action on the continent. At the forefront of these disasters in Africa are recurrent mudslides, landslides and flooding across the continent, particularly in South and East Africa. 

The International Federation of Red Cross notes that within a month (August to September) 2020, more than 1.21 million people in 12 different countries have been affected by floods across Africa, and many other countries are currently experiencing more widespread rainfall than usual in the long rain season leading to transboundary flooding in several areas. Countries most affected by floods during the said five weeks are; Sudan, South Sudan, Ethiopia, Somalia, Uganda, Kenya, Cameroon, Niger, Nigeria, Chad and Mali. More countries are in trajectories of being affected by floods.

In a 2019 analysis by Save the Children, the organisation reported that the climate crisis contributes to at least 33 million people in the region – or 10% of the population across ten countries – being at emergency levels of food insecurity or worse. Over 16 million are believed to be children.

Understanding the crisis and its inherent hazard, the Kenyan Red Cross Service (KRCS), commissioned a study towards seeking sustainable solutions, especially for Kenya and the East African region. This is a breakdown of the pertinent answers provided in the study. 

The KRCS Study

According to the study, Kenya is mostly affected by mudslides and floods during two rainfall seasons, namely March-April-May (MAM) and October-November-December (OND). These landslides, floods and mudslides more often than not lead to loss of human lives, destruction of houses, displacement of people, livestock deaths, loss of livelihoods, among other impacts. The paper highlighted the use of Earth Observation (EO) satellite imageries from the Airbus foundation for post-disaster impact assessment during the 2019 OND rainfall season to support an effective response. On the 23rd of November 2019 during the OND rainfall season, mudslides and floods occurred in West Pokot resulting in disruption of road accessibility, loss of human lives, loss of livelihoods, houses destruction and displacement of people.

To further understand how to assess and diagnose the challenges, a collaboration was born. The study notes that due to the continuation of rainfall, roads were cut-off and hence it was difficult to access the area to determine the damage and the number of households affected. This led to a partnership with Airbus Foundation, International Center for Humanitarian Affairs (ICHA) at Kenya Red Cross Society (KRCS), tasking the Pleiades satellite to acquire imageries of the affected areas five days after the mudslide event.

The study has, therefore opened the door for a very important conversation on the role of Earth Observation in understanding and averting disasters. 

The importance of Earth Observation 

According to the Group on Earth Observations (GEO), EO is the gathering of information about planet Earth’s physical, chemical and biological systems. It involves monitoring and assessing the status of, and changes in, the natural and man-made environment. In recent years, EO has become more and more sophisticated with the development of remote-sensing satellites and increasingly high-tech “in-situ” instruments. Today’s EO instruments include floating buoys for monitoring ocean currents, temperature and salinity; land stations that record air quality and rainwater trends; sonar and radar for estimating fish and bird populations; seismic and Global Positioning System (GPS) stations; and over 60 high-tech environmental satellites that scan the Earth from space. EO is now more important than ever due to the dramatic impact that modern human civilization is having on the global environment.

Utilising EO is therefore no longer a luxury for nations, but is increasingly becoming a need, that more countries have to benefit from. This is why KRCS’ solution is focused primarily on EO and its components and how it can be impactful to understanding and solving the inherent disaster challenges. 

The study mentions that with impacts arising whenever major flood and mudslide events occur, the uptake of EO satellites within the humanitarian sector has happened at an unprecedented rate over the last decade. Obtaining reliable information by gathering evidence on the ground is often limited in flood and mudslide situations due to limited accessibility and time criticality. In such a context, remote sensing can improve hazard assessment and management. Remote sensing is a cost-effective technology where one can accurately extract information about a disaster, e.g. a flood, from an area using satellites without having direct contact to this location.

It notes further that, remote sensing has proven to be a cost-effective asset for humanitarian aid. This is as highlighted in table 1 below. The table highlights the benefits of remotely sensed data as compared to conventional ground mapping in enhancing humanitarian action during disaster events.

Satellite imagery has been employed to guide humanitarian response to natural disasters, including floods and mudslides, for example, in response to the Philippines landslides and the south-east Asia tsunami. Within the context of the south-east Asia tsunami in 26th December 2004, two post-disaster and pre-disaster high spatial resolution satellite imageries allowed easy and quantitative damage assessment through visual change detection. The post-disaster imagery was a satellite archive captured in 30th January 2003 while the pre-disaster imagery was acquired in 29th December 2004 – 3 days after the disaster event. This enabled delineation of tsunami-affected areas and thus enabled disaster managers to assess the damage and to supply local logistic teams to affected areas. On 17th February 2006, a landslide triggered by heavy rains buried the village of Saint Bernard in the Philippines. Several satellite sensors were used to derive a landside extent layer that delineated areas affected by the mudslide. The landslide extent was derived by means of on-screen digitization. The two global examples highlight how satellite imageries are applied in the rapid mapping of disasters and thereby enhancing crisis management support in a timely and cost-effective manner.

How the EO data was deployed

The study notes that the Airbus Foundation has enabled KRCS to task optical and radar satellites in inaccessible and remote areas that have been greatly affected by a disaster within a short timeframe without necessarily dispatching rescue teams on the ground to assess the extent of damage through conventional ground surveys. In so doing, KRCS has been able to accurately conduct disaster assessments to communities affected in a cost-effective and timely manner. This was the case during the Solai Dam burst in 2018, where the timely acquisition of the Pleiades imagery from the Airbus foundation enabled the extraction of 223 households that were affected by the dam burst. With this accurate figure, KRCS was able to disburse unconditional cash to the 223 affected households in Solai to access safe and dignified alternative housing. 

With ground assessments to determine the magnitude of damage greatly hampered by harsh weather conditions and impassable roads, on the 28th of November 2019, KRCS once again resorted to the use of earth observation satellites from the Airbus Foundation. The aim of this was to acquire two post-disaster and pre-disaster satellite imageries to allow quantitative damage assessment through visual change detection, thus enabling delineation of floods and mudslide affected areas by means of on-screen digitization. KRCS tasked the Pleiades satellite to capture imageries over affected areas. 

Visual analysis and comparison of Pleiades imageries allowed for the identification of landslide scars and flood extents. These were consequently used to determine areas affected by both hazards. At 0.5m resolution, it was possible to create a detailed outline of freshly exposed soils, flood-movement, swollen rivers and concave structures identified as possible landslide scars in a number of locations, indicating potentially unstable slopes. Change detection analysis undertaken through image enhancement and visual interpretation revealed destruction of natural vegetation and farmlands such as uprooting of trees and shrubs and burying of crops. Other adverse impacts on the environment that were interpreted from the acquired EO satellites included waterlogging that compromised on the surface and underground water systems. Indicative of the devastation to settlements, farmlands, natural vegetation and waterlogging as a result of mudslides and floods, maps generated from this study provided useful information on areas that need humanitarian support in terms of recovery and rehabilitation.

The spatial analysis results for the covered areas indicate that 180 houses were completely destroyed by both floods and mudslide hazards, while 95 houses were partially damaged. In addition, 2.1 kilometres of roads were cut-off by the events. Therefore, the affected communities and infrastructure destroyed can be accurately detected within a short-timeframe and lead an effective response. The mudslide and flood hazard maps were used by KRCS to initiate shelter re-construction in the 275 houses that were destroyed by both floods and mudslide hazards. The results obtained using remote sensing appear very promising, especially since the technology allows mapping of flooded areas and hazard exposure analysis to identify residents marooned by floodwaters, damaged structures and inaccessible roads due to the floods and mudslides. This study has demonstrated the valuable use of satellite imageries from the Airbus Foundation to KRCS through the provision of timely and accurate information on impacts of mudslides and floods in remote and inaccessible areas in a cost-effective manner. This strongly concurs with the benefits of remote sensing in humanitarian action. During disasters, such high-resolution data can be used as reference maps suitable for early assessments and emergency response.

How the Kenyan solution can be replicated across-continent

The KRCS study has proven the role of EO before the occurrence of a disaster, during the occurrence and after the occurrence. It also covers how governments can respond to disasters in the future, and why they need to use EO data in proferring solutions. Conclusively, the study mentions that KRCS and other national societies should utilize satellite products for post-disaster assessment since the affected areas may be inaccessible due to the hazard. At the same time, the interpretation of satellite imagery can provide a timely perspective on the extent of the hazard. This would improve their capacity for conducting post-disaster assessments in a cost-effective and timely manner. Additionally, it would strengthen humanitarian data preparedness by extracting accurate information on hazard extent and accurate identification of affected households which is imperative for effective disaster response.