In some regions, rapid increases in human uses of stored water and streamflow can reduce water availability in the long term. A 2013 study indicated that human water consumption increased the intensity of the 1988 North American hydrologic drought. The same study showed that human water consumption increases hydrologic drought frequency by 20–25 percent for North America. In the United States, much of this excess water consumption is from irrigated agriculture; the exception is the eastern United States, where most water consumption is for industrial and domestic use [16].

In a similar fashion, farming practices can impact the severity and duration of agricultural droughts by reducing soil moisture. The 1930 “Dust Bowl” was triggered by an extended period of abnormally low precipitation levels across the Midwest, made worse by farming techniques that made the soil vulnerable to increased evapotranspiration and thus reduced the soil moisture available for crops [7].

Finally, climate change can exacerbate drought triggers. Changes to climate, whether anthropogenic or natural in cause, can exacerbate drought, although scientifically modeling the exact impacts of climate change on precipitation deficits remains challenging. Scientists project increased average land surface temperatures in the western United States, and in California in particular [17]. This increase in average temperature can lead to milder winters, decreased snowpack, and increased soil moisture deficit. These factors might contribute to both hydrologic and agricultural drought in the region. Similarly, decreases in soil moisture within the top 10 cm of the soil is projected across the United States due to increasing average temperatures.

[7] National Drought Policy Commission, “Preparing for Drought in the 21st Century,” U.S. Department of Agriculture, Washington, D.C., 2000.

[16] Y. Wada, et al., “Human water consumption intensifies hydrological drought worldwide,” Environmental Research Letters, vol. 8, p. 034036, 2013.

[17] United States Global Change Research Project, “Our Changing Climate,” in Impacts, Risks, and Adaptation in the United States: Fourth National Climate Assessment, Volume II, D. Reidmiller, et al., eds., Washington, D.C.: USGCRP, 2018.