Time series of estimated global hydrological drought frequency with pristine conditions (climate variability only), with fixed consumptive water use of 1960 (1960 consumption), and with 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