L A B ARCA FANTASMA

This section will review the state of knowledge of climate change impacts on water resources, agriculture and biodiversity in East Africa.

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2.3.1 Temperature and Precipitation

Many studies conclude that temperatures across Africa are projected to increase faster than the global average (Joshi et al., 2011; James and Washington, 2013). Projections of changes to precipitation in East Africa are more uncertain than projections of temperature changes (Rowell, 2012). Alterations to precipitation across East Africa are likely to be extremely complex, with significant seasonal and spatial variations (Orlowsky and Seneviratne, 2012). de Wit and Stankiewicz (2006) show that large parts of East Africa may experience an increase in annual average rainfall with climate change. Hulme et al. (2001) and Dessu and Melesse (2013) further this argument, suggesting that in general, precipitation across East Africa is likely to increase between December and February. By contrast, Patricola and Cook (2010) projected lower rainfall across much of East Africa for August and September.

Adhikari et al. (2016) compared the results of previous projections of precipitation change for the East African countries. They found that increases in precipitation are projected for Ethiopia, Kenya, Tanzania, Uganda and Rwanda by the 2090s. By contrast, no substantial changes to rainfall were projected for Malawi,

Mozambique or Zambia. However, substantial uncertainty in the projections, due to the different emissions scenarios and climate models, was also apparent. There are still large uncertainties in GCM projections of large-scale precipitation changes across Africa (Hulme et al., 2001). In East Africa, rain can occur in isolated

patches or broad bands (Douglas et al., 2008). Rain falling in discrete patches would be more difficult to project using large-scale climate models.

2.3.2 Water Resources

Climate change is projected to bring elevated levels of runoff in some countries of East Africa. Runoff is a particularly important part of understanding water

resources, as it will be affected by both changes in temperature (through

evapotranspiration) and precipitation. Areas that experience increases in runoff during the rainy seasons may not also experience a reduction in water shortages (Githui et al., 2009). Instead, as these increases in runoff only occur over short time periods (from rainfall in single storms), they are more likely to lead to flooding. Milly et al. (2005) compared the results of 12 different climate models and found that runoff in eastern African is likely to increase by between 10 and 40%.

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As precipitation and runoff evolve, so will the volume and timing of water entering and travelling through the river network. Arnell (1999) used the HadCM3 model to examine changes in water resources with climate change. Results showed that across East Africa, high flows are likely to increase whereas low flows are

projected to decrease significantly by the 2050s. This conclusion is supported by the smaller-scale research of Githui et al. (2009), who modelled future flows in the Nzoia River Basin, Kenya. High flows were projected to increase in the future, with greater increases in the 2050 period. However, there was also greater uncertainty between the different models in the 2050 period than the 2020s. The highest increases in baseflows were seen in the December to February rainy season. Dessu and Melesse (2013) have shown similar results, using the SWAT model to show that river flows in the Mara River Basin (Kenya/Tanzania) in the wet seasons are likely to increase but little change is projected for the dry seasons. Mati et al. (2008) also examined the Mara River, finding evidence that high flow incidents are increasing in frequency and occurring earlier in the season. Kim and Kaluarachchi (2009) projected changes in annual runoff of between -25 and +32% for the Upper Nile basin by the 2050s. This shows that there is a significant amount of

uncertainty in the projections for this area. These studies show that there is a large amount of spatial variability in projected changes, suggesting both increases and decreases in flows could occur in the East African region.

2.3.3 Agricultural Change

Research into the potential impacts of climate change on agriculture in East Africa is less developed than global scale research. Overall, climate change is expected to reduce crop yields in Africa due to shorter growing sessions, increased

occurrence of pests and diseases and increased water stress (Niang et al., 2014). Adhikari et al. (2015) reviewed previous studies on the potential impacts of climate change on fourteen staple and cash crops in eastern Africa. They found

substantial reductions in yields, with wheat the most vulnerable of the crops. Thornton et al. (2009) found considerable spatial and temporal variation in crop response across the East African region. Mountainous areas may experience increases in crop yields, whereas lowland areas are more likely to see reductions in yields. In the past, the relatively lower temperatures limited crop yields at higher elevations, but as the climate changes, these areas may become more suitable for crop growth. There are large uncertainties in the response of some crops (Lobell

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2030s across food-insecure regions of the world. For East Africa, models

projected decreases in production for cowpea, beans, sugarcane, with cowpea the most negatively affected. Contrastingly, increases in production were projected for wheat. Lobell et al. (2008) found that the models disagreed on the sign of the change in production for maize and sorghum. As maize is the most widely cultivated crop in sub-Saharan Africa (Smale et al., 2011), there is a significant volume of research into how it may be affected by climate change. Most studies conclude that maize will be negatively affected (Lobell and Field, 2007; Nelson et

al., 2009). Similarly, sorghum is an important crop in East Africa as it is able to

grow in a wide range of temperatures and rainfall patterns (Wortmann et al., 2009). Previous studies have shown that sorghum is likely to be more resilient to changes in climate than maize, but that reductions in yields are still possible (Liu et

al., 2008; Nelson et al., 2009; Knox et al., 2012).

Some studies focus on high value crops. Jaramillo et al. (2011) found that the coffee berry borer (Hypothenemus hampei) was already benefiting from higher temperatures and could significantly impact coffee production in East Africa. The negative effects of climate change on Coffea arabica yields in East Africa was also noted by Craparo et al. (2015), who focused on the Tanzanian highlands. Areas suitable for both tea and coffee production are expected to shift towards higher altitudes (Adhikari et al., 2015).

2.3.4 Biodiversity Loss

Research into biodiversity change on the regional scale for Africa is limited, as studies tend to focus on smaller regions or single ecosystems within the individual countries. However, East Africa is identified as an area of concern in some global- scale analyses (Foden et al., 2013). Research has also shown that a large

proportion of East African species are already facing threats. The IPBES (2018) shows that nearly 40% of species endemic to East Africa are classed as

‘vulnerable’ or higher risk (i.e. endangered, critically endangered, extinct in the wild or extinct) by the IUCN Red List. This is the highest proportion for any region of Africa.

2.3.5 The Importance of Extreme Climatic Events

ECEs produce a disproportionately large volume of climate-related damages, although many impact assessments focus on the mean change in climate (Katz and Brown, 1992; Seneviratne et al., 2012). Flooding is a regular occurrence in

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many parts of East Africa, with the two wet seasons often leading to biannual flooding along many major rivers. Haile et al. (2013) examined damage from flooding in Ethiopia and found that although large floods occurred several times in the last decade, the most damage was done by the 2007 inundation, where heavy rainfall extended for around 8 weeks. As urban populations continue to expand and anthropogenic impacts on the land and drainage intensify, the risk of flooding in East African towns and cities increases (Douglas et al., 2008). However, as Whitfield (2012) correctly notes, detecting changes in flood regimes that are due to anthropogenic climate change is extremely difficult as natural variability is also important.

Studies of droughts in East Africa are fairly limited in comparison (Hastenrath et

al., 2007), but research has shown that historically drought-prone regions are likely

to experience a greater risk in the future (Fu and Feng, 2014; Prudhomme et al., 2014; Lehner et al., 2017). Droughts can be broadly classified into three

categories: meteorological drought, agricultural drought and hydrological drought. Droughts can affect both surface and groundwater resources, and therefore need to be carefully considered when discussing water resources management. 9 out of the top 10 disasters in Kenya from 1900 to 2018 in terms of total number affected have been droughts (EM-DAT, 2018). 4 of these droughts have occurred in the last 10 years. By contrast, floods cause more economic damage. A similar

situation is seen for Tanzania and Uganda, with the majority of top 10 disasters in terms of numbers affected being either a flood or drought (EM-DAT, 2018). Once again, the floods caused more economic damage.

Extreme heat is also projected to affect African countries in the future. Russo et al. (2016) found that many African countries are projected to experience regular heat waves by the 2040s. Similarly, Weber et al. (2018) found that longer and more frequent heat waves are likely even if the global mean temperature rise remains below 2°C. Heat waves will have indirect impacts on multiple sectors, including human health and agriculture.

Furthermore, as well as understanding the changes in ECE occurrence, it is necessary to understand the vulnerability of the local people. Adger et al. (2003) showed that the populations of developing countries have traditionally been the most resilient to both droughts and floods. However, Dai (2011) argues that

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ECEs do increase in magnitude and frequency in the future, East Africans may be unable to effectively deal with the consequences.