Past and projected rainfall and temperature trends in a sub-humid Montane Forest in Northern Kenya based on the CMIP5 model ensemble

Citation:
Muhati GL, Olago D, Olaka L. "Past and projected rainfall and temperature trends in a sub-humid Montane Forest in Northern Kenya based on the CMIP5 model ensemble." Global Ecology and Conservation. 2018;16:e00469.

Abstract:

Abstract

This study presents past and projected temporal changes in mean temperature and rainfall around the Marsabit Forest Reserve (MFR), a sub-humid montane forest in Kenya. Rainfall data for the period 1961–2014 and temperature data for the period 1972–2011 were acquired from the Marsabit meteorological station. Future projections (2006–2100) were based on data from five models that participated in the Coupled Model Intercomparison Project Phase 5 (CMIP5) under Representative Concentration Pathways (RCPs) 4.5 and 8.5. Climate simulations for the 2071–2100 period were compared to the 1961–1990 IPCC baseline period to establish significant change. The MFR recorded a mean rainfall of 784 mm which declined annually at a rate of 6 mm over the period of the study. The long rains (March–May) recorded a mean of 379 mm and decreased annually by 10 mm while the short rains (October–December) recorded a mean of 269 mm and decreased annually by 2 mm between 1961 and 2014, with no statistically significant trend (p > 0.05).

The model ensemble reproduced the MFR bimodal rainfall pattern, but overestimated the short rains at 333 mm, compared to the actual mean of 269 mm, and underestimated the long rains at 331 mm, compared to the actual mean of 379 mm. The model ensemble simulated a historical mean rainfall of 651 mm compared to the actual mean of 784 mm. Annual rainfall is projected to increase under both scenarios with higher increases during the OND season compared to the MAM season and under RCP8.5 than under RCP4.5. The mean rainfall in the baseline year was 859 mm while the mean rainfall in the projection period for the RCP4.5 and RCP8.5 scenarios is expected to be 1022 (+19%) and 1105 (+28.7%) mm, respectively; significant enough to be characterized as climate change.

Temperatures are projected to increase at a rate of 0.2 °C and 0.5 °C per decade under RCP4.5 and RCP8.5, respectively. Between 2071 and 2100, the MFR is projected to have warmed by between 1.2–1.7 °C and 3.2–4.8 °C under RCP4.5 and RCP8.5, respectively. Extreme rainfall events are projected to increase under the RCP4.5 scenario (severe wetting 13.1%, severe drying 3%) and the RCP8.5 scenario (severe wetting 20.1%, severe drying 3%) compared to the baseline period (severe wetting 6.1%). Our results conform to the ‘East African climate paradox’, where the observed rainfall trends were declining compared to the scenario simulations projecting a wetting anomaly as local temperatures rise. Further studies to better understand the cause of the poor rainfall simulation in the general circulation models (GCMs) in the MFR and the larger East African region will be necessary.

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