204
D. O. Olago et al.
scenarios, this would be in the range of RCP6.0 estimates (IPCC 2014). There are
large uncertainties related to evapotranspiration estimation methods (Hamon and
FAO Penman-Monteith) “since no data to properly estimate the evapotranspiration
is available” (MEWNR and JICA 2013). Changes in evapotranspiration have knockon impacts on the water balance of runoff, soil moisture, and surface and groundwater
reservoirs (Bates et al. 2008). Given these uncertainties, the NWMP 2030 adopted the
lower FAO Penman-Monteith method results as they offered a cautionary note to the
development of the water resources. Despite these uncertainties, models generally
predict that renewable water resources are likely to increase, and that, excluding
factors such as water abstractions and a shift in the P:E ratio, the volume of water
held in the lakes will increase in future.
The projected temporal and spatial distributions of the mean annual rainfall in
2030 and 2050 are similar to the climate of 2010, but the western part of Kenya is
expected to be wetter with more rainfall in the MAM season, while the eastern part
will be drier, due to potential increased evapotranspiration (MEWNR & JICA 2013).
This is consistent with the findings of Shongwe et al. (2011), based on analysis of an
ensemble of 12 CMIP3 GCMs (forced with A1B emissions), that show statistically
significant widespread increases in short season (OND) rainfall, including extreme
precipitation across East Africa. Stocker et al. (2013) also project increased short rains
in East Africa due to the pattern of Indian Ocean warming, and increased rainfall
extremes related to landfall cyclones on the east coast. Similar to the CORDEX
analysis (Misiani 2013), the model ensemble used by Shongwe et al. (2011) was
relatively poor in simulating the MAM season.
3 The Climate-Environment-Society Nexus in Lake Basins
The recent rise in water levels of the central rift lakes since 2010 (Figs. 3 and 4) and
its effects have been a key subject of discussion in the country (see Box 1). Its impacts
include submerged buildings, infrastructure, and displacement and/or disruption of
the productivity of both humans and wildlife, including aquatic species. However,
some of the infrastructures around the lakes, such as Lake Naivasha, have been built
on what was likely previously riparian land because the water levels were that high
in the first half of the twentieth century.
These discussions have taken center stage because there has been no clear change
in rainfall amounts or patterns that is perceptible to humans, as occurs during ENSO
events, and results of instrumental data analysis are ambiguous. For example, one
early report suggests that the increase in Lake Nakuru’s surface area from a low of
31.8 km
2 in January 2010 to a high of 54.7 km
2 in September 2013 was caused by
an increase in the mean annual precipitation in the period 2009–2014 (e.g., Onywere
et al. 2013). By July 2019, it had not recovered to average levels (Fig. 4). Indeed, all
the lakes in Kenya’s central rift valley (Nakuru, Bogoria, Baringo, Solai, and Logipi)
have risen since 2010 to levels not seen in the last fifty years (Fig. 3). Moreover,
some of the lakes exceeded the well-known and -documented historical high levels
D. O. Olago et al.
scenarios, this would be in the range of RCP6.0 estimates (IPCC 2014). There are
large uncertainties related to evapotranspiration estimation methods (Hamon and
FAO Penman-Monteith) “since no data to properly estimate the evapotranspiration
is available” (MEWNR and JICA 2013). Changes in evapotranspiration have knockon impacts on the water balance of runoff, soil moisture, and surface and groundwater
reservoirs (Bates et al. 2008). Given these uncertainties, the NWMP 2030 adopted the
lower FAO Penman-Monteith method results as they offered a cautionary note to the
development of the water resources. Despite these uncertainties, models generally
predict that renewable water resources are likely to increase, and that, excluding
factors such as water abstractions and a shift in the P:E ratio, the volume of water
held in the lakes will increase in future.
The projected temporal and spatial distributions of the mean annual rainfall in
2030 and 2050 are similar to the climate of 2010, but the western part of Kenya is
expected to be wetter with more rainfall in the MAM season, while the eastern part
will be drier, due to potential increased evapotranspiration (MEWNR & JICA 2013).
This is consistent with the findings of Shongwe et al. (2011), based on analysis of an
ensemble of 12 CMIP3 GCMs (forced with A1B emissions), that show statistically
significant widespread increases in short season (OND) rainfall, including extreme
precipitation across East Africa. Stocker et al. (2013) also project increased short rains
in East Africa due to the pattern of Indian Ocean warming, and increased rainfall
extremes related to landfall cyclones on the east coast. Similar to the CORDEX
analysis (Misiani 2013), the model ensemble used by Shongwe et al. (2011) was
relatively poor in simulating the MAM season.
3 The Climate-Environment-Society Nexus in Lake Basins
The recent rise in water levels of the central rift lakes since 2010 (Figs. 3 and 4) and
its effects have been a key subject of discussion in the country (see Box 1). Its impacts
include submerged buildings, infrastructure, and displacement and/or disruption of
the productivity of both humans and wildlife, including aquatic species. However,
some of the infrastructures around the lakes, such as Lake Naivasha, have been built
on what was likely previously riparian land because the water levels were that high
in the first half of the twentieth century.
These discussions have taken center stage because there has been no clear change
in rainfall amounts or patterns that is perceptible to humans, as occurs during ENSO
events, and results of instrumental data analysis are ambiguous. For example, one
early report suggests that the increase in Lake Nakuru’s surface area from a low of
31.8 km
2 in January 2010 to a high of 54.7 km
2 in September 2013 was caused by
an increase in the mean annual precipitation in the period 2009–2014 (e.g., Onywere
et al. 2013). By July 2019, it had not recovered to average levels (Fig. 4). Indeed, all
the lakes in Kenya’s central rift valley (Nakuru, Bogoria, Baringo, Solai, and Logipi)
have risen since 2010 to levels not seen in the last fifty years (Fig. 3). Moreover,
some of the lakes exceeded the well-known and -documented historical high levels