Extreme Rainfall and Flooding in the East Usambaras – Challenges and Solutions

Extreme rainfall in recent weeks in the East Usambara Mountains, one of AFRICAP’s study sites in Tanzania, has led to severe cases of flooding and landslides. Whilst seasonal rainfall is usual for this time of year in the Usambaras, such a high level of rainfall is unprecedented.  

As part of The AFRICAP programme of work, we are working with local and Government organisations in Tanzania to understand the effects of climate change on food and agricultural systems. Part of this process is the development of a robust evidence base, to support informed decision-making. In this blog, AFRICAP researchers Hemant Tripathi, Joseph Galani, Samuel Eze, Sarah Chapman and Harriet Smith reflect on their current research in the East Usambaras, and provide insights on likely outcomes and potential support systems, to help cope and adapt to such extreme rainfall events. 

What are the impacts of extreme rainfall? 

Extreme rainfall and flooding has multiple direct and indirect consequences on agricultural systems, such as impacts on soil, crop pests and fungal contamination. These all have multiple and complex outcomes for rural livelihoods. For example, flooding reduces the soil’s capacity to support crop production and breaks down soil structure, which makes the soil unstable and can result in landslides. Flooding accelerates soil erosion, which causes physical damage to crops and trees, spread of soil-borne pathogens and loss of organic matter and nutrient-laden topsoil. Muddy runoff is a sign of accelerated soil erosion; in the East Usambaras, much of the topsoil from the highlands ends up in Sigi River, which supplies water to the Regional Capital of Tanga. 

Local Agricultural Extension Officers, Mr Florence Moshaand Mr Manzil Ally, have reported that many of the crop fields in highland areas have experienced extensive gully erosion, and it is highly likely that the recent flood events in the East Usambara Mountain have worsened the soil health and stability of the area. Landslides occurred in multiple areas; soils that took millions of years to form were lost entirely. The loss of soil is not the only impact however, as landslides can devastate farms. The picture below shows a landslide that occurred in a spice farm; spice farms take decades to cultivate and provide essential and reliable income generation for many families in the East Usambaras. In one event, a lifetime of investment and a family’s livelihood can be ruined. 


Landslide in a spice farm in the East Usambara Mountain, Amani area (photo taken October 2019).
Landslide in a spice farm in the East Usambara Mountains, Amani area (photo taken October 2019)


On-going AFRICAP research in the Usambara Mountains is examining the impacts of climatic events, including heavy rain and flooding, on farming systems and livelihood outcomes. Interviews with farmers have highlighted multiple challenges arising from extreme, and unpredictable rainfall, ranging from reduced harvests, increased food insecurity, reduced access to markets and financial loss, with consequential impacts on planned household spending.  

For example, as one farmer states: “the rainfall during the month of May (2019) was too much and also delayed from the usual time of March. This affected the productivity of our farms. Too much rainfall also destroyed the roads making it difficult to sell any crops. This affected my family’s income, and delayed the construction of our family home. 

And, as another farmer explains: “The major [challenge] I have faced is too much rain, which occurred last year in 2018. […] The situation has brought a big loss to my family because I won’t harvest what I expected. This has led my family to face food shortages, and caused me to run out of money and I was unable to hire labourers to assist me in my farming activities. 


Damage to roads disrupts access within mountain regions (photo taken in the East Usambara Mountains, Amani area – October 2019)


Floods and intense rains are also associated with decreases in abundance, biomass, and diversity of invertebrate communities. Impacts of the recent flooding event may result in a reduction in species and functional diversity, which can disrupt critical ecosystem services such as pest control, nutrient cycling, and pollination. Flooding events can also devastate local ecological communities, leading to the survival of the few species well adapted to recolonizing the disturbed environments. This results in a more homogenized community dominated by generalist insect groups, such as crickets and beetles, which aggravate pest crop damage.  

Crop pest control is already an issue for many smallholder farmers in the Usambara Mountains: “There are pests we call Shongo (cereal stem borers), they are very destructive. These pests occur every year. There are impacts to the family as well because it ran us into shortage of food.”  

Changes in climate are known to affect the prevalence of certain pests, which some farmers are already observing: “Insects continued to affect because of the climatic changes, maize crops were highly affected. They led to decline of harvest hence decline of income.”  

Mycotoxins are toxin contaminants of crops such as maize, groundnuts and spices, which are produced by moulds or fungi. Fungal contamination usually occurs in fields throughout the cropping season. During this time, the fungus develops and subsequently produces high amount of toxins during postharvest processing and storage. Environmental factors that increase fungal contamination and mycotoxin production are warmer temperatures and higher moisture or water activity. It is possible that the recent heavy rains have generated moist conditions that promote fungal growth. Heavy rains and flooding can keep farmers out of their fields, leaving their harvest in the field for longer than anticipated, which can lead to further mycotoxin contamination.


An example of soil erosion in the East Usambara Mountains, Amani area (Photo taken October 2019).
Soil erosion in the East Usambara Mountains, Amani area (Photo taken October 2019)


What does the future look like? 

Through the AFRICAP programme of work, we are modelling projections of future climate change. Examination of a number of climate models (CORDEXCP4 and P25) suggest that by the end of the century consecutive wet days are expected to decrease. However, extreme rainfall (high intensity, in a short amount of time), similar to recent events, is expected to increase in the wet seasons across Tanzania. The models suggest larger increases in the October-December (OND) rainy season, particularly on the northeast coast where the Usambara Mountains are located. March-May (MAM) extreme rainfall is also expected to increase, though to a lesser degree than OND rainfall. The higher resolution model CP4 suggests that rainfall intensity in MAM will increase more in the East Usambara Mountains than in the West; OND rainfall will increase similarly across both areas. The fact that multiple models show similar projections increases the confidence in these results. 


Difference between historical and end of century high intensity rainfall for CORDEX multi-model mean, CP4 and P25 high emission scenario, business as usual (RCP8.5)
Difference between historical and end of century high intensity rainfall for CORDEX multi-model mean, CP4 and P25 high emission scenario, business as usual (RCP8.5)


How can farmers adapt to increased prevalence of extreme rainfall and flooding 

One possible approach to minimise the impacts of extreme rainfall and flooding, and also help farmers cope and adapt to increasingly erratic rainfall, is climate-smart agriculture (CSA). CSA is an approach that unites the agendas of climate change, development and agriculture, and ensures consideration of climate-induced risks in agricultural planning. It typically integrates a suite of practices that help farmers cope with increased climate variability and climate-induced shocks and stresses. 

Certain CSA practices have been promoted in the East Usambara area, as part of The European Union’s Global Climate Change Alliance (GCCA+) climate adaptation programme. These include the construction of terraces, contour planting and growing grass strips, which all help to stabilise the soil and reduce erosionAgroforestry, through the planting of spice trees has been promoted as an alternative livelihood strategy to crop farming and to sequester carbon. Planting trees in mountain areas can also help support soil structure. However, as recent events have shown, trees alone cannot prevent landslides.

The programme promoted use of manure and organic homemade pesticides and has introduced and supported farmers on the use of improved seed varieties that are faster maturing, so can cope better with rainfall fluctuations. The programme has also promoted triple-lined crop storage bags, which protect stored crops from pest damage and fungal (including mycotoxin) contamination. 

Despite the benefits of CSA practices however, farmers still face challenges with their adoption. Unpredictable weather affects how people understand and value CSA practices, as one farmer explained: “I have not received any of the significant benefits from [CSA] farming practices, due to challenges with unreliable rainfall. Even if you use all of the proper practices, if the rain is not coming you will not get any production from the farm. So I don’t know which practice is more effective and which ones are less effective.”  

Another critical challenge to farmers adopting practices is often due to their financial and labour capacities, despite their desire to implement CSA. For example, one farmer described how: “This year, there was too much rain. As a result, there has been little harvest. This has encouraged me to make terraces and grow improved seed varieties. However, I am facing a challenge with financial income. If I had money, I would have sought for some labourers to assist me [to build the terraces], but I do not have that money.” 

Our ongoing interdisciplinary research across AFRICAP aims to develop better understanding of how CSA practices are performing and how farmers can be supported, in order to enhance the evidence-base on CSA. Generating and sharing new learning on what does and does not works on farms, and what support farmers need and want, is essential to developing more resilient livelihoods and food security in this region, and more broadly across Tanzania.