Comparison of standardized deficit volumes (—) with (left) pristine condition and with (middle) transient human water consumption, and (right) relative contribution of human water consumption (%) for major drought events over (a)–(c) North America (2002), (d)–(f) Europe (2003), and (g)–(i) Asia (2001)

<p><strong>Figure 2.</strong> Comparison of standardized deficit volumes (—) with (left) pristine condition and with (middle) transient human water consumption, and (right) relative contribution of human water consumption (%) for major drought events over (a)–(c) North America (2002), (d)–(f) Europe (2003), and (g)–(i) Asia (2001). We tested whether the change due to human water consumption is significant by calculating the standard error from observed and simulated standardized deficit volume (under transient human water consumption) for all drought events over each basin (see supplementary material, available at <a href="http://stacks.iop.org/ERL/8/034036/mmedia" target="_blank">stacks.iop.org/ERL/8/034036/mmedia</a>). We used the average standard error over all basins as an estimate for all drought events. We then compared the change to two times average standard error (<em>p</em>-value < 0.05) to test the significance. Areas with significant change are highlighted with dark-gray lines.</p> <p><strong>Abstract</strong></p> <p>Over the past 50 years, human water use has more than doubled and affected streamflow over various regions of the world. However, it remains unclear to what degree human water consumption intensifies hydrological drought (the occurrence of anomalously low streamflow). Here, we quantify over the period 1960–2010 the impact of human water consumption on the intensity and frequency of hydrological drought worldwide. The results show that human water consumption substantially reduced local and downstream streamflow over Europe, North America and Asia, and subsequently intensified the magnitude of hydrological droughts by 10–500%, occurring during nation- and continent-wide drought events. Also, human water consumption alone increased global drought frequency by 27 (±6)%. The intensification of drought frequency is most severe over Asia (35 ± 7%), but also substantial over North America (25 ± 6%) and Europe (20 ± 5%). Importantly, the severe drought conditions are driven primarily by human water consumption over many parts of these regions. Irrigation is responsible for the intensification of hydrological droughts over the western and central US, southern Europe and Asia, whereas the impact of industrial and households' consumption on the intensification is considerably larger over the eastern US and western and central Europe. Our findings reveal that human water consumption is one of the more important mechanisms intensifying hydrological drought, and is likely to remain as a major factor affecting drought intensity and frequency in the coming decades.</p>