Simulation of present-day climate of tropical Africa Using the Hadley Centre

regional climate modeling system

AIACC AF 20 Project

Andre F. KAMGA , Gregory. S. Jenkins , Amadou T. Gaye , Adamou Garba , A.

Sarr, and A. Adedoyin

 

African tropics experiences a highly variable climate and

presents a significant vulnerability to probable

climate change.

Acquiring knowledge of possible future climate change for the next decades will facilitate design and

implementation of adaptation strategies.

• Numerical simulations with Global Circulation Models (GCMs) are appropriate tools to address global to sub-continental scale climate change and impacts ( Giorgi et al. 2002)

• To address country, sub-country and local scale climate change consequences or impacts, high resolution climate Scenarios are required. Regional Climate Models (RCM) are tools to develop high resolution climate scenarios.

• We examine hereunder a RCM simulation of some aspects of present-day (61-90) climate of tropical Africa.

Why do we examine models simulations?

• To guide future improvements of climate models

• To facilitate interpretation and use of models climate forecasts or climate change scenarios.

The Boundary Conditions Are Provided by a 30 Year ( 1961-1990) Integration of

HADAM3H Which Is an Atmospheric Higher Resolution (150 Km) Version of

HADCM3.

Precis is a regional climate modeling system developed by UK Metoffice Hadley Centre

for climate prediction and research.The Hadley center regional climate

modeling system have been used to conduct experiments over Europe, India and

Southern Africa.

PRECIS TEMPERATURE SIMULATIONS AND

NCEP/CDAS REANALYSIS.

Temperature Climatology

• Temperatures above 30°C at sub-country scale are simulated with positive Biases up to 2°C.

• Regional monthly variability of temperature is well captured by Precis.

• Locations with high temperatures ( > 30°C) are well simulated by PRECIS RCM.

• Therefore, there may be some skill in capturing areas at a sub-country scale that may experience temperatures above a given threshold in future

climate scenarios with Precis.

PRECIS PRECIP SIMULATIONS AND CRU

ANALYSIS.

• Precipitation is overestimated over the ITCZ .

• Regional annual cycle of precipitation is well captured.

• Heavy precipitation locations in the ITCZ core are simulated.

• Therefore, there may be some skill in capturing areas that may experience heavy precipitation or flooding

with overestimation of precipitation intensity.

Discussions

• There is generally a surface temperature warm bias (1-2°C) over much of land

areas. A systematic strengthening of St Helena High as well as the low-level

monsoon winds (warm air masses) are common behavior of many GCMs.

Therefore, the warm bias in the RCM is probably related to circulation bias of the

driving GCM.

• Moreover, a tropospheric cold bias in the tropics has been noted in the driving GCM leading to a reduction of static stability, promotion of convective ascent, and intensification of the hydrological cycle.

• The observed overestimation of precipitation in the RCM over ITCZ is probably related to biases in the circulation and temperature profiles of the driving GCM.

CONCLUSION« The annual cycle of precipitation and

temperature are well simulated by the RCM from sub-continental to sub-country scales. Sub-continental to sub-country scale areas that have experienced heavy precipitation and high temperatures are reasonably well

captured. »RCM runs with Reanalysis as driving data may shed some lights on the extent to which

the main source of RCM biases are the driving GCM data.

To improve our capacity to interpret and To improve our capacity to interpret and use models, extensive validation use models, extensive validation

experiments are needed and relationships experiments are needed and relationships between scenarios verification and between scenarios verification and

scenarios value could be investigatedscenarios value could be investigated..“ If forecasts or a climate change scenarios do

not contain the information one needs, or are not presented in a manner such that one can

extract that information then one simply stops buying them and speaks badly of them in cities

wine bars or sue the forecasts vendors.”