© Crown copyright Met Office Providing High-Resolution Regional Climates for Vulnerability Assessment and Adaptation Planning Joseph Intsiful, African Adaptation Programme

© Crown copyright Met Office Climate scenario “A scenario is a coherent, internally consistent and plausible description of a possible future state of the world. It is not a forecast; rather, each scenario is one alternative image of how the future can unfold.” Key point 1: Internal consistency Socio-Economic scenario → Emissions scenario → Climate scenario Key point 2: Scenarios are NOT the same as ‘predictions’: we can have many plausible scenarios. Climate scenarios

© Crown copyright Met Office Types of climate scenarios Incremental scenarios for sensitivity studies Analogue scenarios Scenarios based on outputs from Climate Models

© Crown copyright Met Office Particular climatic elements are changed incrementally by plausible though arbitrary amounts. Use for testing system sensitivity Use for identifying critical thresholds or discontinuities in climate Potentially leads to unrealistic scenarios Not related to anthropogenic emissions 1. Incremental scenarios

© Crown copyright Met Office Identify recorded climate regimes which may resemble the future climate in a given region. Spatial analogues Temporal analogues Palaeoclimatic Instrumental Not related to anthropogenic emissions Often physically implausible 2. Analogue scenarios

© Crown copyright Met Office Coupled Atmosphere-Ocean Global Climate Models (AOGCMs) Coarse resolution, and often have large biases Based on physics Internally consistent Dynamically downscaled AOGCMs High resolution GCMS (e.g. PRECIS) Require large computer resources Can inherit biases from AOGCM Statistically downscaled AOGCMs Statistical methods are based on current climate and trained on short-term variability Difficult to develop internally consistent climate variables 3. Scenarios based on outputs from Climate Models

© Crown copyright Met Office Predicting impacts IPCC National research centres You! CORDEX

© Crown copyright Met Office … from a global climate model (GCM) grid to the point of interest. Downscaling

© Crown copyright Met Office 300km Global Model 25km Regional Model 50km Regional Model Observed 10km Winter precipitation over Britain

© Crown copyright Met Office Regional climate models (RCMs) simulate high resolution weather

© Crown copyright Met Office RCMs simulate extreme events e.g. tropical cyclones

© Crown copyright Met Office Represent smaller islands Projected changes in summer surface air temperature between present day and the end of the 21st century.

© Crown copyright Met Office What is a Regional Climate Model? Mathematical model of the atmosphere and land surface (and sometimes the ocean) ‘High’ resolution: Produces data in grid cells < 50km in size Spans a limited area (region) of the globe Contains representations of many of the important physical processes within the climate system Cloud Radiation Rainfall Atmospheric aerosols Soil hydrology etc.

© Crown copyright Met Office Boundary conditions Limited area regional models require meteorological information at their edges (lateral boundaries) These data provide the interface between the regional model’s domain and the rest of the world The climate of a region is always strongly influenced by the global situation These data are necessarily provided by global general circulation models (GCMs) or from observed datasets with global coverage

© Crown copyright Met Office More adverse than beneficial impacts on ecological and socioeconomic systems are projected

© Crown copyright Met Office Evaluation of the detrimental and beneficial consequences of climate change on natural and human systems. Impacts models require climate scenarios as inputs. The impact of the climate change is determined by contrasting the effect of the observed/baseline climate with that of the future climate (scenario) on the exposure unit Impacts Assessment

Using climate model scenarios with impact models To assess an impact a baseline needs to be established, i.e. the impacts model needs to be run with baseline climate information This baseline climate information can either be taken from a climate model simulation of present-day conditions or directly from observations If the baseline climate information is taken from a model simulation of current climate then the future climate scenario can be derived directly from a future climate simulation If the baseline climate is taken from observations then climate change scenario information from a climate projection needs to be combined with this baseline to provide the future climate scenario The impacts model is then run either of these future climate scenarios and the results compared with the impact baseline © Crown copyright Met Office

One approach to combining climate observations and simulations If, as a result of systematic biases in the GCM/RCM simulations, the impact baseline is unrealistic then a simple approach is to apply the model change factor rather than the model output directly Model change factor = Model future – Model baseline: or Model change factor =(model future / model baseline) *100 We can then add the change factor to an observed record to get a future scenario with the bias seen in the baseline removed Future climate scenario = Observed + model change factor: or Future climate scenario = Observed * model change factor (%) This approach may provide impact results which are more reasonable but the simple change factor applied does not account for changes in variability and may result in inconsistent future climates © Crown copyright Met Office

Example: Modelling Impacts of climate change on agriculture Use of PRECIS and the crop model CERES to simulate yield changes per hectare of three grain crops (rice, wheat, maize) in China when applying one future climate scenario and a representation of CO2 fertilization Xiong et al, 2007, Climate change and critical thresholds in China’s food security, Climatic Change, 81:

© Crown copyright Met Office Example: modelling climate change impacts on Hydrology Change in water stress in the Ganges-Brahmaputra-Meghna Basin derived using the Global Water Availability Assessment (GWAVA) model (CLASIC project – work with CEGIS) 2020s 2050s

© Crown copyright Met Office Example: Modelling Storm Surge under climate scenarios Simulated tropical cyclone and resulting storm surge. Produced using PRECIS and POLCOM storm surge model SLR projections from GCM

© Crown copyright Met Office An impacts case-study

© Crown copyright Met Office Climate change scenarios from a recent climate model: estimating change in runoff in southern Africa Nigel Arnell (Dept. of Geography, University of Southampton, U.K.) Debbie Hudson and Richard Jones (Hadley Centre for Climate Prediction and Research)

© Crown copyright Met Office Methods Runoff: calculated from water balance runoff = precipitation – evaporation – absorption by soil Two sets of models - a climate model and a runoff model Baseline climate → Run-off model → Baseline Run-off Future climate → Run-off model → Future Run-off Compares different methods of constructing future climate scenario

© Crown copyright Met Office Mean temperature and rainfall Average annual rainfall is systematically over- estimated by the model

© Crown copyright Met Office Rainfall variability is accurately represented by the model

© Crown copyright Met Office Constructing the baseline and future timeseries of data required by the runoff model. For example: …these are just some of the possibilities Some different methods for CCS construction

© Crown copyright Met Office

The best method CCS construction in this case?

© Crown copyright Met Office Summary There are several techniques for producing future climate information Only climate model based climate change predictions can be used for providing climate scenarios which are plausible and self consistent Even when using a single climate model (or family of models) there are many different ways to provide climate change information for impacts studies The method of climate scenario construction adds a further uncertainty in assessing impacts of climate change

© Crown copyright Met Office Questions and answers