206
D. O. Olago et al.
which occurred in 1961, and/or in the early 1900s (Schagerl and Renaut 2016, and
references therein).
Box 2: Why the rise in water levels in Kenya rift lakes since 2011?
Several hypotheses from formal and informal discussions were proposed in
2013 to explain the rising lake levels in recent times—they are the opinions
(not scientific findings) of several scientists who have researched the lakes.
These hypotheses may have inter-related causes; exact cause(s) are currently
being investigated.
Hypotheses for the rise in water levels in the lakes include
1. A primarily climatological effect affecting Rift lakes that are all situated in
the same climate region. Their hydrological character as ‘amplifier lakes’
implies that relatively minor changes in the amount and seasonal distribution of (catchment-wide) rainfall and evaporation results in strong lake
level response.
2. Intensified land use in recent decades and the resulting land degradation,
which is severe in some areas, have resulted in higher rainfall runoff from
land, and less percolation of it into groundwater systems, leading to larger
volumes of water flowing directly and rapidly from the land surface into
the lakes.
3. The rainfall runoff over degraded lands and enhanced soil erosion as well
as degradation of the lakes’ riparian zones has decreased the depths of
the lakes through enhanced sediment inputs, shallowing them very rapidly.
Thus, while volumes of water flow into the lakes and volume retention
within them may remain essentially the same, there is an increase in the
lake levels due to the shallowing effect of rapid sedimentation (similar to
the siltation effect in man-made dams).
4. The impact of land degradation and related runoff flows to the lakes is
enhanced because it causes more water to flow into the lakes via (faster)
river inflow than via (slower) shallow groundwater input.
5. Geological factors such as tectonic uplift.
6. Inter/multi-decadal to centennial scale cyclical variability of the climate
system in the lake region has been inferred from geological records, and
cannot be captured from the short instrumental records that currently exist
in the country.
Satellite monitoring of surface area fluctuations in Lakes Bogoria, Nakuru, and
Elementaita reveals temporally congruent responses during the period 2000–2013,
while Lake Logipi showed a response that was different to these lakes, but similar
to Lake Natron (Emma Jayne Tebbs 2014). Whether or not the change in rainfall
is the main driver of lake level changes is still, however, inconclusive, because the
cause(s) of the rise in the other lakes has not been ascertained. It can be seen, for
example, that from the mid-1950s up to the year 2005, discharge fluctuations in the
D. O. Olago et al.
which occurred in 1961, and/or in the early 1900s (Schagerl and Renaut 2016, and
references therein).
Box 2: Why the rise in water levels in Kenya rift lakes since 2011?
Several hypotheses from formal and informal discussions were proposed in
2013 to explain the rising lake levels in recent times—they are the opinions
(not scientific findings) of several scientists who have researched the lakes.
These hypotheses may have inter-related causes; exact cause(s) are currently
being investigated.
Hypotheses for the rise in water levels in the lakes include
1. A primarily climatological effect affecting Rift lakes that are all situated in
the same climate region. Their hydrological character as ‘amplifier lakes’
implies that relatively minor changes in the amount and seasonal distribution of (catchment-wide) rainfall and evaporation results in strong lake
level response.
2. Intensified land use in recent decades and the resulting land degradation,
which is severe in some areas, have resulted in higher rainfall runoff from
land, and less percolation of it into groundwater systems, leading to larger
volumes of water flowing directly and rapidly from the land surface into
the lakes.
3. The rainfall runoff over degraded lands and enhanced soil erosion as well
as degradation of the lakes’ riparian zones has decreased the depths of
the lakes through enhanced sediment inputs, shallowing them very rapidly.
Thus, while volumes of water flow into the lakes and volume retention
within them may remain essentially the same, there is an increase in the
lake levels due to the shallowing effect of rapid sedimentation (similar to
the siltation effect in man-made dams).
4. The impact of land degradation and related runoff flows to the lakes is
enhanced because it causes more water to flow into the lakes via (faster)
river inflow than via (slower) shallow groundwater input.
5. Geological factors such as tectonic uplift.
6. Inter/multi-decadal to centennial scale cyclical variability of the climate
system in the lake region has been inferred from geological records, and
cannot be captured from the short instrumental records that currently exist
in the country.
Satellite monitoring of surface area fluctuations in Lakes Bogoria, Nakuru, and
Elementaita reveals temporally congruent responses during the period 2000–2013,
while Lake Logipi showed a response that was different to these lakes, but similar
to Lake Natron (Emma Jayne Tebbs 2014). Whether or not the change in rainfall
is the main driver of lake level changes is still, however, inconclusive, because the
cause(s) of the rise in the other lakes has not been ascertained. It can be seen, for
example, that from the mid-1950s up to the year 2005, discharge fluctuations in the