# Projections for Temperature and Rainfall

Inputs for temperature and rainfall for the climate change scenarios were based on analysis of a subset of nine GCMs<sup>17</sup> and three emission scenarios (SRES A2, A1b, and B1)<sup>18</sup> used for IPCC AR4. In order to synthesize the myriad of climate projections, which often have conflicting messages,<sup>19</sup> a step-by-step process was followed. First, pattern downscaling (daily timescale Bias-Corrected Spatial Disaggregation) was applied to project maximum monthly temperature and total monthly rainfall for each GCM and emission scenario for 2050.<sup>20</sup> Second, we ranked the models from low to high based on their median projections. Finally, to capture the uncertainty of the extent of climate change, three GCMs (IPS-CM4L, MIROC3.2, and ECHO-G) with the highest, medium, and lowest ranks and the corresponding projections were selected.

The scenario projections include a temperature increase in Bangladesh of about 2.6 to 8 percent for the A2 scenario, 3.3 to 8.2 percent for the A1b scenario, and 3.3 to 7.1 percent for the B1 scenario by 2050. The rainfall projections for 2050 are the following ranges: 30.9 percent decrease to 26.4 percent increase for the A2 scenario, 6.9 percent decrease to 21.9 percent increase for the A1b scenario, and 23.4 percent decrease to 21.2 percent increase for the B1 scenario (see Table 3).<sup>21</sup> 17CCCMA-GCM3.1 is the Canadian Centre for Climate Modeling and Analysis; CNRM-CM3 is the Centre National de Recherches Météorologiques, Météo France, France; ECHAM5/MPI-OM is the Max Planck Institute for Meteorology, Germany; ECHO-G is the Meteorological Institute of the University of Bonn (Germany) and the Institute of KMA (Republic of Korea) and Model and Data Group; GFDL-CM2.0 and CM2.1 are the Geophysical Fluid Dynamics Laboratory, NOAA, USA; IPS-CM4L is the Institut Pierre Simon Laplace, France; MIROC-MIROC3.2 is the CCSR/NIES/FRCGC, Japan; and MRI-CGCM2.3.2 is the Meteorological Research Institute, Japan.

> **18** The A1b scenarios are characterized by rapid economic growth, global population that reaches nine billion in 2050 and then gradually declines, quick spread of new and efficient technologies, a convergent world (income and way of life converge between regions), extensive social and cultural interactions worldwide, and balanced emphasis on all energy sources. The A2 scenarios are characterized by a world of independently operating, self-reliant nations; continuously increasing population; and regionally oriented economic development. The B1 scenarios are characterized by rapid economic growth as in A1, but with rapid changes toward a service and information economy; population rising to nine billion in 2050 and then declining as in A1; **r** eduction **s** in material intensity and the introduction of clean and resource efficient technologies; and emphasis on global solutions to economic, social, and environmental stability. 19For the Ganges basin, although climate models somewhat agree that temperatures will increase significantly, there is wide variation in the direction and magnitude of rainfall predictions.

20 Provided by the climatewizard.org website http://climateknowledgeportal.climatewizard.org/ and the World Bank Group’s Climate Change Knowledge Portal, <u>http://climateknowledgeportal.worldbank.org.</u> 21It should be noted that for the Ganges basin, predictions regarding rainfall vary widely; and different GCMs point to the possibility of either increasing or decreasing rainfall (World Bank 2013).

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