ABOUT MBDI
Calculating MBDI
How the MBDI Compares
Using MBDI
Funder & Affiliates
Introduction: Timing is everything
Drought grips the landscape at different scales, from a short-term effect on the greenness of plants to a long-term effect on the height of groundwater in wells. What’s more, timing matters when it comes to precipitation supply and evaporative demand – some months or seasons wield a greater influence than others on how drought affects natural resources.
So, for instance, reservoir levels are more likely to be affected by a longer-term drought, often on the scale of years. Meanwhile, the overall greenness or health of vegetation as measured by satellite imagery tends to reflect shorter term climatic conditions of three to six months.
The ongoing investigation into the effectiveness of the MBDI for predicting drought impacts has so far focused on three key areas of research:
1) Water Resource Fluctuations
2) Wildfire Hazard
3) Vegetation Greenness
In some cases, the importance of the cool season versus the warm season depends on geography. In mountainous areas where snow can cover the landscape, winter precipitation may have a greater influence on the MBDI ranking of an area. In low desert, on the other hand, summer climate may have a bigger influence on the annual MBDI ranking.
The amount of variance in water year drought explained by conditions in winter (November-April) averages about 55 percent throughout the Colorado River Basin, while the amount explained by summer conditions (July-September) averages about 31 percent. Subtracting the amount explained by summer variance from winter variance highlights how winter conditions dominate in water year values for topographically complex high elevations, while summer conditions play an important role in deserts, including low-elevation deserts and high-elevation desert plateaus in northeastern Arizona and eastern Utah.
Beyond the vagaries of geography, climatic conditions during some months may be more influential than during others for certain drought impacts. For instance, an unusually dry period from April through May can spark numerous large fires, even if precipitation was above normal that preceding winter. In fact, a wet winter can lead to abundant fires in low-lying desert because it promotes the growth of grasses that convert into tinder upon drying.
Researchers continue to explore which time scales and seasons best relate to different landscape impacts. Scientists interested in testing MBDI rankings against their own data are encouraged to contact the MBDI team.
Caption for intext graphic: The amount of variance in water year drought explained by conditions in winter (November-April) averages about 55 percent throughout the Colorado River Basin, while the amount explained by summer conditions (July-September) averages about 31 percent. Subtracting the amount explained by summer variance from winter variance highlights how winter conditions dominate in water year values for topographically complex high elevations, while summer conditions play an important role in deserts, including low-elevation deserts and high-elevation desert plateaus in northeastern Arizona and eastern Utah.
Credit: Andrew Ellis and Jorge Arteaga
