2006–2015 mega-drought in the western USA and its monitoring from space data

Abstract

During 2014 and early 2015, scientific and online publications strongly focused on the multi-year drought over the western USA, showing its dramatic consequences for the US economy, environment and society. Considering such an extraordinary drought, many questions related to its beginning, duration, dynamics, intensity, genesis, extent and frequency became unanswered and even became controversial. How different is this current event from the extraordinary US drought of the 1930s and other intensive droughts? Can this drought be classified as a mega-drought? This paper attempts to answer most of these questions, by applying National Oceanic and Atmospheric Administration (NOAA) global operational satellite system estimating vegetation health. It has been shown that the latest western US drought began in 2006 and has continued for nine full years. Since vegetation stress still continues in the first few months of 2015 (when this paper is written) coming into the 10th year, this drought was classified as a “mega-drought”. In 2006, when the drought began, vegetation was stressed in over 61% of the western USA. During 2012 and 2013 (time of the drought's intensification), this area increased to 71% and 67%, respectively. All 17 states of the western two-thirds of the USA were affected by this drought, especially South Dakota, Nebraska, Oklahoma, Texas, Montana and Wyoming with up to 100% of the area affected by severe vegetation stress during 2012–2014. Compared to other catastrophic droughts of the past 100 years, the current drought during the worst year (2012), affected 71.3% of the western USA. This is comparable to the area affected by a catastrophic drought in 1934 (71.6%) and much higher than the droughts in 1956 (49%) and 1988 (31%). In terms of number of drought years, the other droughts in the western USA (1985–1986, 1988–1992, 1995–1996, and 2001–2003) were shorter and less intensive. Among western states, California was the most severely drought-affected, especially in 2014, when areas of stronger than moderate vegetation stress reached 70%.