(a) Comparison of per drought event simulated deficit volumes (m³) under pristine conditions (climate variability only) and under transient human water consumption with those calculated from observed streamflow in a logarithmic scale over 23 major river basins that are affected by human water consumption

<p><strong>Figure 1.</strong> (a) Comparison of per drought event simulated deficit volumes (m³) under pristine conditions (climate variability only) and under transient human water consumption with those calculated from observed streamflow in a logarithmic scale over 23 major river basins that are affected by human water consumption. The observed streamflow was taken from the selected GRDC stations closest to outlets. (b) Frequency distribution of correlation coefficient and slope per river basin from (a). Five worst drought events were selected from each of 23 major river basins. Note that for fair comparison, deficit volume was calculated with the threshold level <em>Q</em>₈₀ that was derived respectively from each streamflow time series: from the GRDC observations; from the simulated streamflow under pristine conditions; from the simulated streamflow under transient human water consumption. River basins (GRDC stations; station number; available period used) selected: Orinoco (Puente Angostura; 3206720; 1960–1990), Parana (Corrientes; 3265300; 1960–1992), Nile (El Ekhsase; 1362100; 1973–1985), Blue Nile (Khartoum; 1663100; 1960–1983), White Nile (Malakal; 1673600; 1960–1996), Orange (Vioolsdrif; 1159100; 1964–1987), Zambezi (Katima Mulilo; 1291100; 1964–2002), Murray (below Wakool Junction; 5304140; 1960–2002), Mekong (Mukdahan; 2969100; 1960–1994), Brahmaputra (Bahadurabad; 2651100; 1969–1993), Ganges (Hardinge Bridge; 2646200; 1965–1993), Indus (Kotri; 2335950; 1967–1980), Yangtze (Datong; 2181900; 1960–1989), Huang He (Sanmenxia; 2180700; 1960–1989), Mississippi (Vicksburg; 4127800; 1960–2000), Columbia (The Dalles; 4115200; 1960–2000), Mackenzie (Norman Wells; 4208150; 1961–2002), Colorado (Yuma; 4152050; 1965–1990), Volga (Volgograd Power Plant; 6977100; 1960–2002), Dnieper (Dnieper Power Plant; 6980800; 1960–1985), Danube (Ceatal Izmail; 6742900; 1960–2002), Rhine (Rees; 6335020; 1960–2002), Elbe (Wittenberge; 6340150; 1960–2002).</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

Sensitivity of estimated hydrological drought frequency (figure 3) to the different percentile thresholds (<em>Q</em>₇₀,<em>Q</em>₈₀, and <em>Q</em>₉₀) 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>₇₀,<em>Q</em>₈₀, and <em>Q</em>₉₀) 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>₇₀,<em>Q</em>₈₀, and <em>Q</em>₉₀) 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

Previous data and model based assessments of hydrological drought

<p><b>Table 1.</b>  Previous data and model based assessments of hydrological drought. </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

Modeling the Response of the Langtang Glacier and the Hintereisferner to a Changing Climate Since the Little Ice Age

This study aims at developing and applying a spatially-distributed coupled glacier mass balance and ice-flow model to attribute the response of glaciers to natural and anthropogenic climate change. We focus on two glaciers with contrasting surface characteristics: a debris-covered glacier (Langtang Glacier in Nepal) and a clean-ice glacier (Hintereisferner in Austria). The model is applied from the end of the Little Ice Age (1850) to the present-day (2016) and is forced with four bias-corrected General Circulation Models (GCMs) from the historical experiment of the CMIP5 archive. The selected GCMs represent region-specific warm-dry, warm-wet, cold-dry, and cold-wet climate conditions. To isolate the effects of anthropogenic climate change on glacier mass balance and flow runs from these GCMs with and without further anthropogenic forcing after 1970 until 2016 are selected. The outcomes indicate that both glaciers experience the largest reduction in area and volume under warm climate conditions, whereas area and volume reductions are smaller under cold climate conditions. Simultaneously with changes in glacier area and volume, surface velocities generally decrease over time. Without further anthropogenic forcing the results reveal a 3% (9%) smaller decline in glacier area (volume) for the debris-covered glacier and a 18% (39%) smaller decline in glacier area (volume) for the clean-ice glacier. The difference in the magnitude between the two glaciers can mainly be attributed to differences in the response time of the glaciers, where the clean-ice glacier shows a much faster response to climate change. We conclude that the response of the two glaciers can mainly be attributed to anthropogenic climate change and that the impact is larger on the clean-ice glacier. The outcomes show that the model performs well under different climate conditions and that the developed approach can be used for regional-scale glacio-hydrological modeling