Drought Monitoring: Historical and Current Perspectives

Drought is a normal, recurring feature of climate throughout the world, with characteristics and impacts that can vary from region to region. Figure 1.1 illustrates the regular occurrence of drought within the United States between 1895 and 2010 with approximately 14% of the country, on average (plotted by black dotted line), experiencing severe to extreme drought conditions during any given year. Drought conditions can persist in a region for several years, as occurred in the United States in the 1930s, 1950s, and early 2000s, and tree ring and other proxy records confirm that multiple-year droughts are part of the long-term climate history for the United States and most other regions around the world (Woodhouse and Overpeck, 1998; Dai et al., 2004; Jansen et al., 2007). Drought has wide-ranging impacts on many sectors of society (e.g., agriculture, economics, ecosystems services, energy, human health, recreation, and water resources) and ranks among the most costly of all natural disasters. For example, in the United States, drought affects more people than any other hazard (NSTC, 2005) and has resulted in 14 “billion-dollar” events since 1980 totaling more than $180 billion (U.S.) in damages and losses (NCDC, 2011). This amount represents 25% of all losses from billion-dollar weather disasters, including hurricanes and floods. Globally, drought along with other natural disasters affects more than 255 million people each year (Guha-Sapir et al., 2004), with an estimated $932 billion (U.S.) in losses since 2001 in the 42 countries ranked highest by the United Nations in terms of the combination of life expectancy, education, and income (Guha-Sapir, 2011). In developing nations, drought impacts can transcend economic losses, triggering severe famine and potentially human mortality