The Real Drought Uncovered

Abstract:

Drought has a major impact on natural and social resources, and is caused by a prolonged deficit in available water. Possible impacts of drought are crop losses, famine, fatalities, power black outs and degraded ecosystems. This shows the need to carefully monitor drought conditions using the appropriate droughts indicators. The indicators should consider differences in drought-generating processes resulting in drought in different components of terrestrial water cycle. The objective of this study is to compare which indicators can be used for monitoring drought in each part of the terrestrial water cycle. A selection of frequently used indicators for different drought types (e.g. SPI for different accumulation periods, PDSI, threshold approach), was used to investigate potential to monitor drought on a global scale. Correlation (R) between indicators was calculated for the major climates and for the whole globe to quantify the unique information content of each indicator and their interchangeability to be used for different drought types. It was found that indicators used to monitor precipitation drought show low correlations (R = 0-0.35) although most of them are calculated in a similar way (e.g. SPI-1 and SPI-3). Indicators for soil moisture drought are more similar (R = 0.2-0.6), while indicators for streamflow drought show the highest correlation (R = 0.5-0.95). Additionally, meteorological drought indicators are not capable to correctly describe soil moisture (R = 0.1-0.6) nor streamflow drought (R = 0-0.4). These findings have implications for drought monitoring systems: (i) for each drought type, which is associated with one or more impacted sectors, a different indicator should carefully be identified; (ii) combined drought indicators are hard to be linked to a specific impact. In addition, studies on trends in drought or projections of future drought should be specific on the drought type to reduce the current confusion in how drought has developed or will develop.