Downscaling
Encyclopedia
In numerical modeling
, downscaling refers to techniques that take output from the model and add information at scales smaller than the grid spacing. Global climate model
s (GCMs) are run at coarse spatial resolution (typically of the order 50000 square kilometre) and are unable to resolve important sub-grid scale features such as clouds and topography
. As a result GCMs can not be used for local impact studies. To overcome this problem downscaling methods are developed to obtain local-scale surface weather
from regional-scale atmospheric variables that are provided by GCMs. In 1997, Wilby and Wigley
divided downscaling into four categories: regression methods, weather pattern-based approaches, stochastic
weather generators and limited-area modeling. Among these approaches regression methods are preferred because of its ease of implementation and low computation requirements.
Numerical weather prediction
Numerical weather prediction uses mathematical models of the atmosphere and oceans to predict the weather based on current weather conditions. Though first attempted in the 1920s, it was not until the advent of computer simulation in the 1950s that numerical weather predictions produced realistic...
, downscaling refers to techniques that take output from the model and add information at scales smaller than the grid spacing. Global climate model
Global climate model
A General Circulation Model is a mathematical model of the general circulation of a planetary atmosphere or ocean and based on the Navier–Stokes equations on a rotating sphere with thermodynamic terms for various energy sources . These equations are the basis for complex computer programs commonly...
s (GCMs) are run at coarse spatial resolution (typically of the order 50000 square kilometre) and are unable to resolve important sub-grid scale features such as clouds and topography
Topography
Topography is the study of Earth's surface shape and features or those ofplanets, moons, and asteroids...
. As a result GCMs can not be used for local impact studies. To overcome this problem downscaling methods are developed to obtain local-scale surface weather
Weather
Weather is the state of the atmosphere, to the degree that it is hot or cold, wet or dry, calm or stormy, clear or cloudy. Most weather phenomena occur in the troposphere, just below the stratosphere. Weather refers, generally, to day-to-day temperature and precipitation activity, whereas climate...
from regional-scale atmospheric variables that are provided by GCMs. In 1997, Wilby and Wigley
Tom Wigley
Tom Wigley is a climate scientist at the University Corporation for Atmospheric Research . He was named a fellow of the American Association for the Advancement of Science for his major contributions to climate and carbon-cycle modeling and to climate data analysis, and because he is "one of the...
divided downscaling into four categories: regression methods, weather pattern-based approaches, stochastic
Stochastic
Stochastic refers to systems whose behaviour is intrinsically non-deterministic. A stochastic process is one whose behavior is non-deterministic, in that a system's subsequent state is determined both by the process's predictable actions and by a random element. However, according to M. Kac and E...
weather generators and limited-area modeling. Among these approaches regression methods are preferred because of its ease of implementation and low computation requirements.