The main causes of floods are intense and/or long-lasting precipitation, snow/ice melt, a combination of these causes, dam break (e.g., glacial lakes), reduced conveyance due to ice jams or landslides, or by a local intense storm [3]. Floods depend on precipitation (not all) intensity, volume, timing, phase (rain or snow), antecedent conditions of rivers and their drainage basins (e.g., presence of snow and ice, soil character and status (frozen or not, saturated or unsaturated), wetness, rate and timing of snow/ice melt, urbanization, existence of dikes, dams and reservoirs [4]. Flooding susceptibility also depends on the topography, i.e. slope of the terrain. Although some flood disasters occur annually, most happen unexpectedly [5].

Floods can destroy critical infrastructure, buildings, roads, and bridges; tear out trees; devastate agriculture; cause mudslides; and threaten human lives [7]. Extreme flooding affects water management, conservation efforts, and hydro morphological altercations of the ecosystem services and human life. The mitigation of the effects of floods requires monitoring of location, extent, time, and depth of the floods [8].

Every year, flooding causes billions of Dollars’ worth of damage across the globe. According to statistics provided by NOAA National Centers for Environmental Information (NCEI), the average annual cost of flooding from 1980 to 2022 in the United States is approximately $4.0 Billion US Dollars. However, the data from the last 5 years shows that flooding nowadays costs $5.9 Billion US Dollars per year [9].

Africa is exceptionally vulnerable to climate variability and change compared to many other regions [10]. Floods represent a major natural hazard in Africa [11], and have strong impacts on the population and their activities, claiming a large toll in terms of fatalities and economic damage [12]. Flood‐related fatalities in Africa, as well as associated economic losses, have increased dramatically over the past half‐century [13]. 

In Africa, more losses occur due to floods than in earthquakes or wildfires. EM-DAT data revealed over 32 000 deaths and approximately 8.7 million affected people in over 1 100 flood events from 1927 to 2022 [14]. Statistics for the reported economic losses due to natural disasters in Africa, for the 1970 – 2019 period, revealed that the cost of floods is around 13.09 billion U.S. Dollars, covering 34% of the total. As presented in Figure 2, floods cover 60% of the total disasters in the depicted period, and 4% of the reported deaths [10]. However, the data shows only reported economic losses; therefore, the actual economic damage caused by floods in African countries is considered to be more severe.

Trans-boundary Floods

Floods do not respect borders, and some rivers even determine national borders. Therefore, trans-boundary flooding is an important topic to focus on. In this case, the approach to floods might change as other parameters are involved in the process. Riparian countries should engage in joint flood management to broaden the knowledge and information base, which in itself will increase their strategic options and allow for better and more cost-effective solutions [15]. It might not be challenging for instance in the European Union, where all countries in the union can take a part in all related processes and embrace a collective approach. However, it is a significant phenomenon for some riparian countries that are strict about their national borders and internal dynamics; i.e. policy, risk management, etc. In this context, some countries tend to avoid joint flood management due to national, financial, historical, and/or other reasons and deal with it internally; i.e. building excessive dams in significant locations to avoid a potential hazard that might come from a riparian country – rather than approaching the risk jointly. Even though riparian countries are involved in joint projects for flood risk management, it is mostly in a technical manner and generally insufficient due to lack of political support which is needed to make technical cooperation sustainable, long-term and effective in the field of trans-boundary water management. In many cases, it is not the technical capacity that is missing, i.e. for flood forecasting, early warning and possible measures, but rather the institutionalization of trans-boundary flood risk management through bilateral and multilateral agreements and continued cooperation [15].

Maritsa River (known as Evros in Greece, and Meriç in Turkey) is amongst the few trans-boundary rivers where floods are the major issue. Not only is the Maritsa River flood-prone, but it also has a strategic importance as it is a border between Greece and Turkey, and hence the European Union (EU) and Turkey [16]. In this context, two EU countries (Bulgaria and Greece) and a non-EU country (Turkey) are riparian and have not yet managed to establish a sufficient joint flood management system and failed in river management and policy due to several reasons in the region/and between these countries including historical, hydro-political and financial issues. Even though Bulgaria and Greece are part of the European Union, it still makes it harder to work jointly against the potential floods due to the geographical power of Bulgaria within the basin, internal issues, national interests, refugee crises, having a non-EU country in the deal, and insufficient support from the EU, etc [16]. Therefore, cooperation between all three riparian states appears to be difficult, inter alia due to differences in institutional structures. Communication between politicians is another challenge [15].

In Africa, Nigeria is one of the countries significantly affected by trans-boundary floods. The country is the flood plain of the trans-boundary Niger and Benue Rivers, which have a number of upstream dams in other countries [17]. Flood flows from the Niger River comes from Guinea, and the Benue River comes from Cameroon and Chad threaten Nigeria and cause severe floods, damage settlements, economy, livelihoods, and cause loss of lives [18]. In 2012, heavy rains between July and October, combined with rising water levels resulting from the runoff contributed to the flooding of human settlements located downstream of the Kainji, Shiroro, and Jebba dams on the Niger River; the Lagdo dam in Cameroon on the Benue River; the Kiri dam on the Gongola River; and several other irrigation dams. In some cases, the dams were damaged; in others, water had to be released at full force to avert an overflow. According to the National Emergency Management Agency of Nigeria (NEMA), 363 people were killed, more than 5 800 were injured, and around 3 900 000 were affected and displaced due to the large-scale trans-boundary floods. Floods in this period caused over $16 Billion in economic damage to Nigeria [19], [20]. Bursting dams, existing urban and regional planning, and insufficient actions aggravate the flooding problem in Nigeria [17]. Cooperation and communication between Nigeria and riparian countries are essential as it will help the region to reduce the damage of trans-boundary floods in the future.

On the other hand, the Grand Ethiopian Renaissance Dam has led to a long political standoff between riparian countries in the region: Ethiopia, Sudan, and Egypt. The Nile Basin river system flows through eleven countries, the Blue Nile and White Nile merge in Sudan before flowing into Egypt and then into the Mediterranean Sea [22]. The massive hydropower plant, the largest in Africa, on the Blue Nile has arisen discussions over time: regarding the control and utilization of the Nile River, power dynamics in the region, energy, and natural hazards such as flood and drought. In early 2022, the project started electricity production as downstream countries, Sudan and Egypt, have been considering the dam as a threat [23]. Sudan hopes that the dam can have a positive effect on flood mitigation during the rainy season, which has not been observed yet [24], and could gain from the dam’s electricity generation [22]. However, Sudan is concerned about the safety of the dam as it is placed just on the other side of its border with Ethiopia, as well as potential damage to its own dams due to the presence of the Grand Dam. Egypt relies on the Nile river for at least 90% of its freshwater, therefore fears that the dam will reduce its share of the Nile waters [22], and is concerned about the management of drought during the years of filling and operating the dam, as well as in the years that follow a natural drought [25]. Egyptian claims are mainly based on the agreement made in 1959 [26]. Ethiopia sees the dam as essential for its development [23], and supposes that the dam would reduce flooding, therefore will protect settlements from flood damage [27]. Ethiopia also depicts that it has been taking the interests of both riparian countries into account, and finds some of the requirements of the Egyptian side unrealistic [22]. The project has also been a field to study a potential failure of the dam, either structural or operational, which might lead to severe flooding and loss of lives, farmlands, and infrastructure in the downstream areas [28].

Floods in Africa – An Overview

53 countries in Africa were affected by flooding from 1927 to 2022. Algeria leads the statistic with 4 895 deaths and 53 events, followed by Somalia with 2 950 deaths and 47 events, and Mozambique with 2 392 deaths and 42 events [14].

Although there were fewer deaths in Nigeria compared to the countries such as Algeria, Somalia, etc., the country ranks first place in total number of people affected by floods, with around 11.75 million people. Detailed statistics by country are presented in Table 1 – sorted by most fatalities [14].

The Role of Earth Observation

Conventional monitoring systems in hydrology have limited capabilities in forecasting, mapping and emergency response in floods. Considering the fact that the cost of maintaining rain and stream gauging stations can be a limiting factor, using freely available earth observation (EO) data can be complementary for adequate flood warning, and allow measuring the spatial extent of the flood over large areas [7]. Rapid delineation of the spatial extent of flooding is of great importance for the dynamic monitoring of flood evolution and corresponding emergency strategies [1]. Remote sensing systems have been widely recognized as suitable resources to offer a synoptic view over large areas and provide valuable information on flood extent and dynamics [29].

Remote sensing techniques offer effective tools for monitoring, analyzing and assessing flooding in various stages of the hazard. EO data from space can help stakeholders, scientists and individuals to monitor, manage and assess flood events in a wide spatial extent since it provides near real-time information without direct contact with the flood area. With the help of remote sensing, it is possible to obtain information to parameterize flood models, delineate flood extent, and estimate flood damage, as well as risk analysis and mitigation. Flood hazard, exposure, and vulnerability modeling at local and regional levels, as well as at a national level, can be supported by remote sensing [30]. Geographical Information Systems (GIS) provide powerful tools for dealing with space data. They are very effective for archiving, displaying, analyzing and modeling geographic data when combining socio-political data such as inhabited areas, these tools are useful for supporting decision-making processes [31]. GIS analysis (with the integration of the Analytical Hierarchy Process) can be used for modeling the magnitude of flood risk areas with rainfall, elevation and slope, drainage network and density, land use, land cover and soil types data [30], [32].

These techniques are not only beneficial during the event, but also during the pre and post stages of the hazard. The stages are commonly divided into the different steps in the disaster management cycle. Figure 4 illustrates the disaster management cycle which has been a crucial and common reference for disaster management [33], [34].

Pre-event activities include prevention, mitigation, and preparedness, whereas the response activities usually include rescue and relief activities, and post-event activities include recovery and development [33]. The prevention stage includes all actions at minimizing future losses that can be caused by floods, the preparedness stage aims at the preparation to the threat of floods and managing them, finally during the event (crisis) and the post-event stages aim at saving lives, minimizing potential impacts, and the improvement/recovery of infrastructure, environment, and human activities [34]. The recovery or development stage can last from months to years depending on the severity of a particular flood hazard, regional/national dynamics, and a country’s resilience.

Both active and passive remote sensing techniques can be used for flood assessment, providing different capabilities and accuracy [35]. Passive (optical sensors) remote sensing rely on solar illumination and measure reflected energy from the sun. Optical sensors measure spectral radiance from the visible through the shortwave infrared spectrum. The near-infrared (NIR) region is the most suitable to distinguish water from dry surfaces due to the strong absorption of water [3], [35]. The Normalized Difference Water Index (NDWI) developed by McFeeters in 1996 [46] has been commonly used for flood mapping. With the calculation of both before and after flood NDWIs, it is possible to expose the extent of a particular flood. NDWI is calculated using Equation 1. 

Modified NDWI variants are able to achieve better output accuracy, such as the Modified Normalized Difference Water Index (MNDWI) introduced by Xu in 2006. MNDWI uses short-wave infrared band (SWIR or MIR) band instead of NIR. The Modified NDWI can enhance open water features while efficiently suppressing and even removing built-up land noise as well as vegetation and soil noise.

Thus, MNDWI overcomes the overestimation of extracted water area that is often mixed with built-up land noise [36]. MNDWI is calculated using Equation 2. 

With the growing number of SAR missions in orbit offering high temporal resolution, data acquired by the SAR sensors is the most commonly used in flood mapping due to their day-night and all-weather imaging capability, facilitating rapid flood mapping in the context of emergency response [29]. In this context, constellations such as Sentinel-1, COSMO-SkyMed, RADARSAT-2, and KOMPSAT-5 provide adequate spatial and temporal resolutions – and TerraSAR-X, which even provides better (sub-meter) resolution [39]. The future of these SAR missions is brighter, with the recent commercial SAR missions such as ICEYE’s microsatellites, and Capella Space, being of great interest to authorities for many needs. SAR-based flood assessment techniques include methods such as threshold-based, image segmentation, statistical active contouring, rule-based classification and data fusion approaches. Among these, threshold-based methods are the most commonly used for flood assessment due to their ease of application [1].

Often, the most appropriate type of sensor for flood assessment is the radar sensor since it can acquire images in cloudy scenes, which is mostly the case during flooding events. However, the processing and analysis of radar data is challenging and requires particular software and expertise [40]. Additionally, SAR-derived flood extent may be underestimated in areas with complex land covers and terrain such as urban areas, forested areas and mountainous areas, due to the side-looking geometry of the sensor that leads to geometric distortions such as foreshortening and layover [1].

Recent Floods in Africa
2022 Malawi Floods

In January 2022, the passage of tropical storm named “Ana” over southern Malawi with heavy rainfall caused rivers overflow, floods and landslides (Figure 7) [41]. Heavy flooding caused by the storm affected the districts in the southern region. Among the 19 affected districts, Chikwawa, Mulanje, Nsanje and Phalombe were the most affected ones as shown in Figure 7. According to the update of United Nations on 11 February 2022, the event caused 46 deaths and 206 injuries, affected about one million and displaced more than 152 000 people [42].

2022 Sudan Floods
Since the beginning of the rain season in June, Sudan experienced a set of destructive floods across the country. In August, when the flooding was the strongest, the hazard caused 146 deaths and 122 injuries - affected about 349 000 people, destroyed at least 24 800 homes and damaged another 48 200 [43].

Among the 18 affected states, the most affected ones were South Darfur, Gedaref, Central Darfur, White Nile, and Kassala, followed by Northern, West Darfur, River Nile, North Kordofan, Aj Jazirah, West Kordofan, South Kordofan, Sennar, and East Darfur. On the other hand, Khartoum and North Darfur were less affected [43].

2020 East Africa Floods
In the first few months of the Coronavirus outbreak, East African countries faced challenging flood events from March to May 2020. The hazard affected countries such as Kenya, Rwanda, the Democratic Republic of the Congo, Ethiopia, Somalia, Uganda, Djibouti, Tanzania, and Burundi. Heavy rainfall that began in March had led to massive flooding and landslides in these countries. The hazard caused about 450 deaths, and thousands of injuries - affected millions, and displaced hundreds of thousands of people [44].

Kenya was the most affected country experiencing severe flood events in April and May, with about 237 deaths and 800 000 affected people. For two months, from March to May, Rwanda had to face challenging flooding events after heavy rain, lightning and thunderstorm. The chain of flooding events took about 97 lives and affected thousands of people across the country. The Democratic Republic of the Congo was also among the most affected countries in this period; 44 people lost their lives and another 200 were injured. Heavy flooding destroyed thousands of buildings, especially households in South Kivu province, and left 64 000 people homeless [44].

In May 2020, after heavy rainfall, Uganda faced a set of destructive floods in the western and northern parts of the country. About 11 people lost their lives, thousands of people were affected, about 5 000 were displaced and many buildings were destroyed across the country. On 9 May 2020, EMS was activated over the hazard in Uganda, and a total of 14 maps were produced and a sample of one of the maps is shown in Figure 9 [44], [45].

References
[1]   M. Zhang, F. Chen, D. Liang, B. Tian, and A. Yang, “Use of Sentinel-1 GRD SAR Images to Delineate Flood Extent in Pakistan,” Sustainability, vol. 12, no. 14, p. 5784, Jul. 2020, doi: 10.3390/su12145784.

[2]   C. B. Field et al., “Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation,” Cambridge, England, 2012.

[3]   L. C. Smith, “Satellite remote sensing of river inundation area, stage, and discharge: a review,” Hydrol. Process., vol. 11, no. 10, pp. 1427–1439, Aug. 1997, doi: 10.1002/(SICI)1099-1085(199708)11:10<1427::AID-HYP473>3.0.CO;2-S.

[4]   B. C. Bates, Z. W. Kundzewicz, S. Wu, and J. P. Palutikof, “Climate Change and Water,” IPCC, Geneva, Switzerland, Technical Report, 2008.

[5]   T. De Groeve, “Flood monitoring and mapping using passive microwave remote sensing in Namibia,” Geomat. Nat. Hazards Risk, vol. 1, no. 1, pp. 19–35, Mar. 2010, doi: 10.1080/19475701003648085.

[6]   J. Bishop, Flooding. 2020. [Online]. Available: https://unsplash.com/photos/4zxp5vlmvnI

[7]   V. Klemas, “Remote Sensing of Floods and Flood-Prone Areas: An Overview,” J. Coast. Res., vol. 314, pp. 1005–1013, Jul. 2015, doi: 10.2112/JCOASTRES-D-14-00160.1.

[8]   F. Carreño Conde and M. De Mata Muñoz, “Flood Monitoring Based on the Study of Sentinel-1 SAR Images: The Ebro River Case Study,” Water, vol. 11, no. 12, p. 2454, Nov. 2019, doi: 10.3390/w11122454.

[9]   A. B. Smith, “U.S. Billion-dollar Weather and Climate Disasters, 1980 - present (NCEI Accession 0209268).” NOAA National Centers for Environmental Information, 2020. doi: 10.25921/STKW-7W73.

[10] “State of the Climate in Africa,” World Meteorological Organization, 2020. [Online]. Available: https://library.wmo.int/doc_num.php?explnum_id=10929

[11] Y. Tramblay, G. Villarini, and W. Zhang, “Observed changes in flood hazard in Africa,” Environ. Res. Lett., vol. 15, no. 10, p. 1040b5, Oct. 2020, doi: 10.1088/1748-9326/abb90b.

[12] Y. Tramblay, G. Villarini, E. M. Khalki, G. Gründemann, and D. Hughes, “Evaluation of the Drivers Responsible for Flooding in Africa,” Water Resour. Res., vol. 57, no. 6, Jun. 2021, doi: 10.1029/2021WR029595.

[13] G. Di Baldassarre, A. Montanari, H. Lins, D. Koutsoyiannis, L. Brandimarte, and G. Blöschl, “Flood fatalities in Africa: From diagnosis to mitigation: FLOOD FATALITIES IN AFRICA,” Geophys. Res. Lett., vol. 37, no. 22, p. n/a-n/a, Nov. 2010, doi: 10.1029/2010GL045467.

[14] D. Guha-Sapir, R. Below, and P. Hayois, “EM-DAT: International Disaster Database,” University Cathol. Louvain, Brussels, Belgium, Database. [Online]. Available: http://www.emdat.be.

[15] United Nations, Ed., Transboundary flood risk management: experiences from the UNECE region. New York ; Geneva: United Nations, 2009.

[16] A. S. Mehta and J. F. Warner, “Multi-level hegemony in transboundary Flood Risk Management: A downstream perspective on the Maritsa Basin,” Environ. Sci. Policy, vol. 129, pp. 126–136, Mar. 2022, doi: 10.1016/j.envsci.2021.12.014.

[17] N. Odume, “Why Nigeria is not prepared to deal with flooding,” The Conversation, 2018. https://theconversation.com/why-nigeria-is-not-prepared-to-deal-with-flooding-104018

[18] H. Aminu Tukur, “Nigerian Hydrological Services Agency’s Efforts Towards Flood Mitigation,” 2021. [Online]. Available: https://www.un-spider.org/sites/default/files/2_NIGERIAN%20HYDROLOGICAL%20SERVICES%20AGENCY%E2%80%99S%20EFFORTS%20TOWARDS%20FLOOD%20MITIGATION_KP.pdf

[19] The Federal Government of Nigeria, The World Bank, and The United Nations, “Nigeria: Post Disaster Needs Assessment - Floods in 2012,” 2013. [Online]. Available: https://www.gfdrr.org/sites/default/files/publication/pda-2012-nigeria.pdf

[20] J. Gbenga, “The Flooding Crisis in Nigeria,” Twentyten Daily, 2020. https://twentytendaily.com/the-flooding-crisis-in-nigeria/

[21] The United Nations, “Reducing industrial pollution in the Niger River Basin.” [Online]. Available: https://www.unido.org/news/reducing-industrial-pollution-niger-river-basin

[22] Aljazeera, “Ethiopia’s Blue Nile mega-dam explained,” Aljazeera, 2022. https://www.aljazeera.com/news/2021/7/8/explainer-ethiopias-massive-nile-dam

[23] Aljazeera, “Ethiopia starts electricity production at Blue Nile mega-dam,” Aljazeera, 2022. https://www.aljazeera.com/news/2022/2/20/ethiopia-electricity-production-gerd-blue-nile-mega-dam

[24] N. Eltahir, “Sudan says Ethiopian dam made no impact on floods this year,” Reuters, 2021. [Online]. Available: https://www.reuters.com/world/africa/sudan-says-ethiopian-dam-made-no-impact-floods-this-year-2021-08-25/

[25] A. M. Melesse, W. Abtew, and S. A. Moges, Eds., Nile and Grand Ethiopian Renaissance Dam: Past, Present and Future. Cham: Springer International Publishing, 2021. doi: 10.1007/978-3-030-76437-1.

[26] I. H. Abdalla, “The 1959 Nile Waters Agreement in Sudanese-Egyptian Relations,” Middle East. Stud., vol. 7, no. 3, pp. 329–341, 1971.

[27] “Grand Ethiopian Renaissance Dam,” Wikipedia. 2022. [Online]. Available: https://en.wikipedia.org/wiki/Grand_Ethiopian_Renaissance_Dam

[28] M. R. Mahmoud, H. Fahmy, and L. A. Garcia, “Potential impacts of failure of the Grand Ethiopian Renaissance Dam on downstream countries,” J. Flood Risk Manag., vol. 15, no. 2, Jun. 2022, doi: 10.1111/jfr3.12793.

[29] L. Yu, “Flood mapping in rural and urban areas with multi-temporal SAR intensity and InSAR coherence,” PHD Thesis, Ludwig-Maximilians-Universität München, Munich, Germany, 2019. [Online]. Available: https://elib.dlr.de/138921/2/Li_Yu.pdf

[30] Y. Wang, “Advances in Remote Sensing of Flooding,” Water, vol. 7, no. 11, pp. 6404–6410, Nov. 2015, doi: 10.3390/w7116404.

[31] N. Suárez Kozov, D. Trujillo Osorio, and J. Giraldo Osorio, “Application of remote sensing for monitoring of flood areas,” RUDN J. Eng. Res., vol. 20, no. 1, pp. 66–78, Dec. 2019, doi: 10.22363/2312-8143-2019-20-1-66-78.

[32] Y. Ouma and R. Tateishi, “Urban Flood Vulnerability and Risk Mapping Using Integrated Multi-Parametric AHP and GIS: Methodological Overview and Case Study Assessment,” Water, vol. 6, no. 6, pp. 1515–1545, May 2014, doi: 10.3390/w6061515.

[33] I. A. Rana, M. Asim, A. B. Aslam, and A. Jamshed, “Disaster management cycle and its application for flood risk reduction in urban areas of Pakistan,” Urban Clim., vol. 38, p. 100893, Jul. 2021, doi: 10.1016/j.uclim.2021.100893.

[34] G. Le Cozannet et al., “Space-Based Earth Observations for Disaster Risk Management,” Surv. Geophys., vol. 41, no. 6, pp. 1209–1235, Nov. 2020, doi: 10.1007/s10712-020-09586-5.

[35] F. Foroughnia, S. M. Alfieri, M. Menenti, and R. Lindenbergh, “Evaluation of SAR and Optical Data for Flood Delineation Using Supervised and Unsupervised Classification,” Remote Sens., vol. 14, no. 15, p. 3718, Aug. 2022, doi: 10.3390/rs14153718.

[36] H. Xu, “Modification of normalised difference water index (NDWI) to enhance open water features in remotely sensed imagery,” Int. J. Remote Sens., vol. 27, no. 14, pp. 3025–3033, Jul. 2006, doi: 10.1080/01431160600589179.

[37] “Comparison of optical and radar imagery, Lake Constance, Germany,” European Space Agency, EO College, 2017. [Online]. Available: https://eo-college.org/courses/echoes-in-space/lessons/history/topic/comparison-to-optical-images/

[38] “Floods imaged by Copernicus Sentinel-1,” European Space Agency, 2019. [Online]. Available: https://www.esa.int/ESA_Multimedia/Images/2019/03/Floods_imaged_by_Copernicus_Sentinel-1#.X5w0pnb7xYc.link

[39] L. Landuyt, A. Van Wesemael, G. J.-P. Schumann, R. Hostache, N. E. C. Verhoest, and F. M. B. Van Coillie, “Flood Mapping Based on Synthetic Aperture Radar: An Assessment of Established Approaches,” IEEE Trans. Geosci. Remote Sens., vol. 57, no. 2, pp. 722–739, Feb. 2019, doi: 10.1109/TGRS.2018.2860054.

[40] T. Perrou, A. Garioud, and I. Parcharidis, “Use of Sentinel-1 imagery for flood management in a reservoir-regulated river basin,” Front. Earth Sci., vol. 12, no. 3, pp. 506–520, Sep. 2018, doi: 10.1007/s11707-018-0711-2.

[41] “EMSR561: Floods in Malawi,” COPERNICUS Emergency Management Service - Mapping, 2022. [Online]. Available: https://emergency.copernicus.eu/mapping/list-of-components/EMSR561/ALL/ALL

[42] “Malawi: Tropical Storm Ana Response, Flash Update No. 2,” United Nations Malawi, Malawi, 2022. [Online]. Available: https://malawi.un.org/sites/default/files/2022-02/Malawi%20Floods%20Flash%20Update%20-%2011%20Feb%202022.pdf

[43] “Sudan Situation Report,” UN Office for the Coordination of Humanitarian Affairs, 2022. [Online]. Available: https://reports.unocha.org/en/country/sudan/

[44] “2020 East Africa Floods,” Wikipedia, 2022. https://en.wikipedia.org/wiki/2020_East_Africa_floods

[45] “EMSR438: Flood in Uganda,” COPERNICUS Emergency Management Service - Mapping, 2020. [Online]. Available: https://emergency.copernicus.eu/mapping/list-of-components/EMSR438

[46]S. K. McFEETERS (1996) The use of the Normalized Difference Water Index (NDWI) in the delineation of open water features, International Journal of Remote Sensing, 17:7, 1425-1432, DOI: 10.1080/01431169608948714