How the MBDI Compares
Funder & Affiliates
The Moisture Balance Drought Index (MBDI) yields values in square pixels of roughly 4,000 acres – about the size of Willcox, Arizona. At this scale, the portion of Arizona in the Colorado River Basin has nearly 22,000 pixels. How do climatologists get values for so many pixels from the 170 weather stations in the state? By considering how elevation, slope and other factors influence local climate using the PRISM approach – designed specifically for mountainous regions.
Precipitation and temperature vary with elevation and other factors. To fill in data gaps between stations, the PRISM model overlays a 2.5 mile by 2.5 mile grid on a three-dimensional relief map of the U.S. and marks the grid-boxes containing weather stations. It then assigns the observed values for precipitation, temperature, and other variables to each box with an established station.
PRISM gets values for remaining pixels by considering how climate differs based on factors such as elevation, proximity to the coast, the topographic lay of the land, the distance to weather stations, and mountainside position in relation to the sun and prevailing winds. The PRISM equations are designed based on observations of how climate varies in mountainous regions.
Developed by Oregon State University researchers, PRISM data covers the continental United States from 1895 to the present. Like the MBDI, coverage exists at the monthly scale. For more details, see the PRISM home page.
PRISM equations work to fill in the spaces between weather stations, resulting in coverage in grid boxes measuring roughly 4-kilometers by 4-kilometers, or 2.5-miles by 2.5 miles.
Credit: Graphic design by Jorge Arteaga