Key Terms for Climate Modeling:
Climate scenario: A climate scenario provides a time series of synthetic weather data with the goal that the statistics of the time series rather than the time series itself will look similar to real-world data.
Global Climate Model (GCM): GCMs are numerical models of physical processes covering the entire globe that is built upon fundamental laws of physics. Models require an initial condition and updates to external forcing mechanisms (such as changes to solar intensity) in order to produce a climate simulation.
Regional Climate Model: Regional climate models are numerical models of physical processes covering a region of the globe that is built upon fundamental laws of physics. Models require an initial condition and updates at the boundaries of the simulation domain. Either an analysis of observations or a global climate model provides data at the boundaries.
Downscale: Downscaling is a modeling technique that creates local or regional data from coarse input data.
Key Terms for Hydrology Modeling
Hydrology: The scientific study of the waters of the earth, especially with relation to the effects of precipitation and evaporation upon the occurrence and character of water in streams, lakes, and on or below the land surface.
Surface Water Hydrologic Models: These are a class of hydrologic models that simulate land surface mass balance for water and, in some models, energy fluxes. Subsurface and soil representation in surface water hydrologic models tend to reflect only shallow-depth soil layers, which contain the more actively “flexed” soil water reservoirs and determine the time-lag between precipitation falling on the watershed and streamflow observed at a downstream location. Examples include: WEAP21 (Physical Module), SAC-SMA/Snow17, and VIC.
WEAP21 – PHYSICAL MODULE: The hydrology framework integrated into the Water Evaluation and Planning (WEAP) platform (www.weap21.org) recognizes that water supply is defined by the amount of precipitation that falls onto a watershed. Specifically the natural watershed process component of WEAP accounts for two different hydrologic realities (Purkey et al. 2007, Yates et al. 2005): (1) the concept that precipitation in upstream watersheds, with complex topography, steep slopes, and abrupt hills and valleys, contributes to gaining streams with a relatively short time lag; and, (2) downstream watersheds with flatter terrain tend to overlie alluvial aquifers, which provide supply to satisfy demands, and are linked to river systems to which they can contribute flow and from which they can receive seepage, depending on hydrologic conditions.
SAC-SMA coupled with SNOW17: The Sacramento Soil Moisture Accounting model (SAC-SMA) is one of operations available in the National Weather Service River Forecast System (NWSRFS) that represents an attempt to parameterize soil moisture characteristics in a manner that would: (1) logically distribute applied moisture in various depths and energy states in the soil, (2) have rational percolation characteristics, and (3) allow an effective simulation of streamflow. The SNOW17 snowmelt model is another operation available in NWSRFS that can be coupled to SAC-SMA, providing snowmelt runoff input to SAC-SMA simulation. It is a conceptual model in which each of the significant physical processes affecting snow accumulation and snowmelt is mathematically represented. The model uses air temperature as the sole index to energy exchange across the snow-air interface and was developed to run in conjunction with a rainfall-runoff model. (Refs. NWSRFS SAC-SMA and NWSRFS Snow17 2005).
VIC: The Variable Infiltration Capacity (VIC) model (Liang et al. 2005, http://www.hydro.washington.edu/Lettenmaier/Models/VIC/VIChome.html) is a macroscale hydrologic model that solves full surface water and energy balances. It was originally developed by Xu Liang at the University of Washington. VIC is a research model and in its various forms it has been applied to many watersheds including the Columbia River, the Ohio River, the Arkansas-Red Rivers, and the Upper Mississippi Rivers, as well as being applied globally.
