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Observed climate change
Mountains are one of the most sensitive ecosystems
to climate change in the world (Kohler and
Maselli, 2012). Globally, mountainous regions have
experienced above average warming during the
twentieth century, a trend that is likely to continue
in the future (IPCC, 2007). Scientists, therefore,
often refer to mountains as early warning systems as
they may provide an indication of the changes that
lowland ecosystems can expect in the future (Kohler
and Maselli, 2012). Specific data on climate change
observations and trends in East Africa’s mountainous
areas are, however, limited; the available data is
mainly for the region as whole. As noted in the
IPCC’s Fifth Assessment Report (2013), there is a gap
in the research on the long-term climate trends for
mountain ecosystems in Africa.
According to the IPCC’s Fifth Assessment Report,
Africa has seen an increase in temperature by 0.5
°C or more during the last 50 to 100 years. The
temperature changes in East Africa are in line with
UNDP Climate Change Country Profiles, which
indicate that both Tanzania and Kenya have had
an increase in temperature of 1.0 °C between 1960
and 2003, while Uganda and Ethiopia have seen an
increase of 1.3 °C over the same period (McSweeny
et al., 2012 a, b, c, d). Data from weather stations
east of the Rwenzori Mountains, located between
960 and 1,869 metres above sea level, indicate an
increase in temperature of 0.5 °C per decade since the
1960s (Taylor et al., 2006). Similarly, an increase in
Climate change trends and scenarios and their effect
on mountain ecosystems
temperature of 0.27 °C per decade has been recorded
near Mount Kilimanjaro (Buytaert et al., 2011). In the
northern part of the Ethiopian Highlands, the average
annual minimum temperature has increased by 0.76
°C between 1954 and 2008, while average annual
maximum temperatures have increased by 0.36 °C
over the same period. This is significantly higher
than the national average of 0.25 °C and 0.10 °C,
respectively (Gebrehiwot and van der Veen, 2013).
There is less certainty on the observed trends in
rainfall across East Africa due to climate models’
difficulties with incorporating the processes affecting
the rainfall patterns in the region. Studies presented
in the IPCC’s Fifth Assessment Report (2013) show
a reduction in rainfall over East Africa during the
past 30 years during the ‘long rains’ between March
and May/June. Similar findings are reported across
the region from Tanzania (Hemp, 2005) and Rwanda
(MoNR, 2012) to Ethiopia (William and Funk, 2011).
Lower rainfall has also been recorded at Mount
Kilimanjaro. Data from three weather stations on
the southern slope of Mount Kilimanjaro indicate
that precipitation has decreased by up to 39 per cent
between 1911 and 2004 (Hemp, 2005). For some areas,
the average annual rainfall has remained more or less
the same, but records show shifts in the rainy seasons
and prolonged dry spells as well as increases in the
intensity of rainfall. There is evidence that extreme
weather events – both heavy rainfall and droughts
– have increased in frequency during the past 30
to 60 years. Based on data from the International
Emergency Disaster Database, Shongwe et al. (2010)
noted a significant increase in hydro-meteorological
disasters in East Africa, from an average of three
events per year in the 1980s to almost 10 per year
between 2000 and 2006. The biggest increase was in
floods, with an increase from one event per year in
the 1980s to seven per year between 2000 and 2006.
These disasters affected about 2 million people a year.
Future climate scenarios
Projections of the future impacts of climate change on
East Africa indicate that the current warming trend
will continue throughout the twenty-first century.
According to the medium-emission scenario of the
IPCC’s Fourth Assessment Report, East Africa can
expect an average increase in annual temperature of
3.2 °C by 2080; ranging between 1.8 °C and 4.3 °C
(IPCC, 2007). The highest increase in temperature
is expected in June, July and August. Based on the
medium-emission scenario, the temperature will
increase by as much as 3.4 °C (ranging between 1.6
and 4.7 °C). Data on climate extremes indicate that the
region will experience an increase in warm days and
nights as well as an increase in the frequency of heat
waves and warm spells (IPCC, 2012; CDKN, 2012).
The IPCC (2013) notes that changes in precipitation
will greatly affect the climate in Africa. There is a
general agreement between the Fourth and Fifth
IPCC Assessment Reports (2007; 2013) that East
Africa will become wetter, both during the ‘long’ and
‘short’ rainy seasons. Future scenarios predict that the
current trend towards a drier climate will reverse. As