Overview & Applicability
The National Climate Change Viewer allows users to visualize projected changes in climate (maximum and minimum air temperature and precipitation) and the water balance (snow water equivalent, runoff, soil water storage and evaporative deficit) for any state, county and USGS Hydrologic Units (HUC) in the continental United States. USGS HUCs are hierarchical units associated with watersheds and analogous to states and counties that span multistate areas. HUC levels 2, 4 and 8 are used in the viewer. The viewer provides a number of useful tools for characterizing climate change including:
- Maps, climographs (plots of monthly averages), histograms that show the distribution or spread of the model simulations, monthly time series spanning 1950-2099, and tables that summarize changes in the quantiles (median and extremes) of the variables.
- Comprehensive, summary reports in PDF format, and CSV files of the temperature and precipitation data for each geographic area.
The National Climate Change Viewer was designed to aid in interpreting output from many climate models in time and space. The USGS developed the tool based on a statistically-downscaled dataset developed by the Climate Analytics Group and NASA Ames Research Center using the NASA Earth Exchange. The initial online launch of the tool was in 2013, and the update with water balance information was released in 2014.
Inputs and Outputs
National Climate Change Viewer offers a straightforward interface for visualizing temperature, precipitation, and water balance data for both past climate and future climate models and scenarios for the years 1950-2099. Users can download PDF summaries for any state, county, or hydrologic unit in the continental United States. CSV files of temperature and precipitation time series are also available for download. Resolution of the climate projections are 800m, however downloadable summaries and data are spatially averaged to the geographic unit (e.g., state, county and watershed).
The main window of the NCCV displays maps of future change (the difference between the historical period and the selected period) in the climate or water balance variables and two accompanying graphs. The map provides a general impression of the spatial variability of change across the continental United States. The climograph compares monthly averages with standard deviations, which are a measure of variability, for the present and future periods. The histogram displays the distribution of change for all model simulations over the selected geographic area.
The Scenario and Time Period tab allows the user to select either the RCP4.5 (stabilized emissions) or the RCP8.5 (unchecked emissions) scenario and a time period of interest:
- 2025-2049 versus 1950-2005
- 2050-2074 versus 1950-2005
- 2075-2099 versus 1950-2005
The dropdown menus across the top of the application are used to select either annual or monthly means, the average of all 30 models (Mean Model) or an individual model (models are listed) and variable of interest. Region Types are selected as states, counties or HUCs and a region of interest is selected under Region.
Basic climate data available are (in English and metric units):
- Maximum air temperature
- Minimum air temperature
Four water-balance variables are included in the viewer (in English and metric units):
- Snow water equivalent, the liquid water stored in the snowpack
- Soil water storage, the water stored in the soil column,
- Evaporative deficit, the difference between potential evapotranspiration, which is the amount of evapotranspiration that would occur if unlimited water were available, and actual evapotranspiration which is what occurs when water is limited
- Runoff, the sum of direct runoff that occurs from precipitation and snow melt and surplus runoff which occurs when soil moisture is at 100% capacity.
Restrictions and Limitations
- The summaries and outputs are static. Therefore, there is no way to produce a customized summary for an area other than a state, county, or hydrologic unit.
- Data are not available for Alaska, Hawaii, or any US territories.
- There is no statistical analysis of past change available. However, users can download time series data to do their own analyses.
- Currently only two Representative Concentration Pathways (RCP) greenhouse gas (GHG) emission scenarios are available.
- Data cannot be downloaded directly from the tool into GIS. Temperature and precipitation data can be downloaded from NASA directly or from the USGS Geo Data Portal and loaded into GIS. The water balance data grid are not available for download yet.
- The approach used in generating the NEX-DCP30 dataset inherently assumes that the relative spatial patterns in temperature and precipitation observed from 1950 through 2005 will remain constant under future climate change.
These limitations should be kept in mind when viewing the water balance components:
- The water holding capacity of the soil column is fixed everywhere at 150 mm (5.9 in),
- Evapotranspiration is computed by a temperature-dependent equation
- The model does not simulate or account for groundwater
- There is no routing of runoff between grid cells so the viewer displays the spatial average runoff within a region
- The parameters used in the model are spatially homogenous and independent of land use, vegetation and elevation
- Because the data are spatially averaged and on monthly time steps, short-term and spatially specific events, such as peak runoff that occurs over several days in high elevation sites, are not resolved.
More discussion on the limitations of the tool can be found at http://www.usgs.gov/climate_landuse/clu_rd/apps/nccv_documentation_v1.pdf