Sensitivity of estimated hydrological drought frequency (figure 3) to the different percentile thresholds (<em>Q</em><sub>70</sub>,<em>Q</em><sub>80</sub>, and <em>Q</em><sub>90</sub>) for pristine conditions (climate variability only) and for transient consumptive water use (transient consumption) over the period 1960–2010 over (a) the Globe, and for each continent; (b) Asia, (c) North America, (d) Europe, (e) Africa, (f) South America, and (g) Oceania

<p><strong>Figure 4.</strong> Sensitivity of estimated hydrological drought frequency (figure <a href="http://iopscience.iop.org/1748-9326/8/3/034036/article#erl471582fig3" target="_blank">3</a>) to the different percentile thresholds (<em>Q</em><sub>70</sub>,<em>Q</em><sub>80</sub>, and <em>Q</em><sub>90</sub>) for pristine conditions (climate variability only) and for transient consumptive water use (transient consumption) over the period 1960–2010 over (a) the Globe, and for each continent; (b) Asia, (c) North America, (d) Europe, (e) Africa, (f) South America, and (g) Oceania. The frequency was derived from the sum of the number of drought events below threshold levels (<em>Q</em><sub>70</sub>,<em>Q</em><sub>80</sub>, and <em>Q</em><sub>90</sub>) for each year over the globe and for each continent. The frequency was indexed per year by dividing the sum by the average drought frequency of the pristine condition calculated with each percentile threshold over the period 1960–2010.</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>