Examination of change factor methodologies for climate change impact assessment

Abstract

[1] A variety of methods are available to estimate values of meteorological variables at future times and at spatial scales that are appropriate for local climate change impact assessment. One commonly used method is Change Factor Methodology (CFM), sometimes referred to as delta change factor methodology. Although more sophisticated methods exist, CFM is still widely applicable and used in impact analysis studies. While there are a number of different ways by which change factors (CFs) can be calculated and used to estimate future climate scenarios, there are no clear guidelines available in the literature to decide which methodologies are most suitable for different applications. In this study several categories of CFM (additive versus multiplicative and single versus multiple) for a number of climate variables are compared and contrasted. The study employs several theoretical case studies, as well as a real example from Cannonsville watershed, which supplies water to New York City, USA. Results show that in cases when the frequency distribution of Global Climate Model (GCM) baseline climate is close to the frequency distribution of observed climate, or when the frequency distribution of GCM future climate is close to the frequency distribution of GCM baseline climate, additive and multiplicative single CFMs provide comparable results. Two options to guide the choice of CFM are suggested. The first option is a detailed methodological analysis for choosing the most appropriate CFM. The second option is a default method for use under circumstances in which a detailed methodological analysis is too cumbersome.

A watershed-scale study of climate change impacts on groundwater recharge (Annapolis Valley, Nova Scotia, Canada)

“…There are a number of other bias correction methods that can be used to account for the systematic mismatch between observed and simulated climate variables (e.g. Anandhi et al 2011, Stoll et al 2011, Sulis et al 2012. Assessments of different techniques and their limitations can be found in Hagemann et al (2011) and Ehret et al (2012).…”

High-resolution Med-CORDEX regional climate model simulations for hydrological impact studies: a first evaluation of the ALADIN-Climate model in Morocco

“…The so-called "delta change" or perturbation method belongs to this type of approach (Anandhi et al, 2011;Ruelland et al, 2012): it consists in perturbing the observed precipitation and temperature series to reproduce the changes observed between the control and future climatic simulations from climate models. The hypothesis behind is that climate models are not necessarily good at reproducing the present climate in a realistic manner (contrary to weather forecast models, they do not assimilate observations for example) but are mainly designed to simulate the trends of the earth climate system related to external forcing (green-house gases, aerosols, solar variation, volcanic eruption).…”

Evaluation of a multi-site weather generator in simulating precipitation in the Qiantang River Basin, East China

“…CFM is a very common method for estimating climate change (Anandhi et al, 2011). Although more complicated methods exist, CFM is still widely applied in many studies.…”

“…Different mathematical formulations are used for different variables. For example, additive change factor (CF) is often used for temperature and multiplicative CF is often used for precipitation (Anandhi et al, 2011). Multiplicative is also used for standard deviation of temperature.…”