A COMPARISON OF DELTA CHANGE AND DOWNSCALED GCM SCENARIOS FOR THREE MOUNTAINOUS BASINS IN THE UNITED STATES¹

Abstract

Simulated daily precipitation, temperature, and runoff time series were compared in three mountainous basins in the United States: (1) the Animas River basin in Colorado, (2) the East Fork of the Carson River basin in Nevada and California, and (3) the Cle Elum River basin in Washington State. Two methods of climate scenario generation were compared: delta change and statistical downscaling. The delta change method uses differences between simulated current and future climate conditions from the Hadley Centre for Climate Prediction and Research (HadCM2) General Circulation Model (GCM) added to observed time series of climate variables. A statistical downscaling (SDS) model was developed for each basin using station data and output from the National Center for Environmental Prediction/National Center for Atmospheric Research (NCEPINCAR) reanalysis regridded to the scale of HadCM2. The SDS model was then used to simulate local climate variables using HadCM2 output for current and future conditions. Surface climate variables from each scenario were used in a precipitation‐runoff model. Results from this study show that, in the basins tested, a precipitation‐runoff model can simulate realistic runoff series for current conditions using statistically down‐scaled NCEP output. But, use of downscaled HadCM2 output for current or future climate assessments are questionable because the GCM does not produce accurate estimates of the surface variables needed for runoff in these regions. Given the uncertainties in the GCMs ability to simulate current conditions based on either the delta change or downscaling approaches, future climate assessments based on either of these approaches must be treated with caution.

Impacts of climate change, land-use change and phosphorus reduction on phytoplankton in the River Thames (UK)

“…Fifteen uniform changes (i.e. using a delta change method, see for example Hay et al, 2000) were applied to the current precipitation series (2011)(2012)(2013)(2014), from -30% to +40% with a 10% step, providing fifteen altered precipitation series. Similarly, fifteen uniform changes were applied to the current air temperature series (2011)(2012)(2013)(2014), from -1°C to +6°C with a 0.5°C step, obtaining fifteen altered air temperature series.…”

Tropical forests and adaptation to climate change: in search of synergies

“…The downscaling technique we used was the simple delta change method. There may be some inaccuracies in this (Gyalistras et al, 1994;Hay et al, 2000) but it is a relatively simple method and can be used quickly for large areas. The difference of the rainfall temperature and diurnal temperature range from the HadCM2 model for the present and 2055 (mean of 2040 to 2069) were calculated ( Figure 2).…”

“…This was added in to the 1975 climate grid. This stage is therefore a simple delta change downscaling (Hay et al, 2000). The MarkSim climate patterns of the 702 clusters can be considered a form of weather typing, see Wilby (1995).…”

Downscaling of Short-Term Precipitation Time Series for Climate Change Impact Assessment

“…precipitation or temperature), as estimated from climate model data, are transferred to historical observations of the same variable [5]. In the SUDPLAN application, future changes of the frequency distribution of 30-min precipitation intensities, which is the shortest time step available in climate model data, are transferred to historical short-term rainfall observations.…”