The vast majority of locally-available fresh water comes either directly from precipitation and groundwater, or indirectly through runoff from distant locations (such as snowmelt). Readily available freshwater resources are substantially altered through natural processes such as rainfall and evapotranspiration, or when the availability is changed both spatially and temporally by human processes such as water diversion and storage, deforestation, and groundwater depletion. Important climate extremes relate to how much or how little precipitation falls over time, snowmelt timing, fluctuations in land evapotranspiration, and soil moisture dynamics. From a climate perspective, it is therefore imperative to understand the natural variability of precipitation and land water exchanges and storages, as well as their susceptibility to change by external forcings.

This Grand Challenge expands on questions related to changes in water storage, both temporally and spatially, with respect to reservoirs, ground water, snowpack depth, and other sources.

More specifically this Grand Challenge embodies the following science questions:

  • What are the effects of changes in the character of precipitation (snow vs. rain, snow water equivalent, etc.)?
  • How do the temporal changes in precipitation regimes affect water availability?
  • How will changes in the mean and variability of precipitation affect human infrastructure?
  • Which regions will see an increase vs. decrease in precipitation?
  • Which regions will see an increase vs. decrease in actual and potential evapotranspiration?
  • Which regions will see an increase vs. decrease in the climatically-available water (P-E)?
  • How are groundwater recharge and availability affected?
  • In which regions can groundwater pumping be sustained in a warmer climate?
  • How is snow cover, depth, and water equivalency affected?
  • In which regions is food production endangered by the expected changes in the water cycle?
  • Which actions need to be undertaken to improve our water management and maintain viable agriculture?
  • How will climate change modify competing interests for water?
  • How are land water exchanges affected by climate change, or affecting themselves regional climate responses (e.g., temperature and precipitation means and extremes)?
  • How are changes in land use and land cover affected by water availability, and how do they affect water availability?