Daniel Collins (via haiku!) notes the important point that water folks are increasingly raising about climate change: it’s not just whether rainfall goes up or down. Increased evaporation and transpiration as the climate warms is the critical water supply variable. From Cai and others in GRL – since 1950, nearly half the reduction in soil moisture in Australia’s Murray Darling Basin can be attributed to increased temperatures:

A relationship exists between soil moisture and temperature independent of rainfall, particularly in austral spring and summer. Annually, a rise of 1°C leads to a 9% reduction in soil moisture over the southern MDB, contributing to the recent high sensitivity. Since 1950, the impact from rising temperature contributes to 45% of the total soil moisture reduction. In a warming climate, as the same process also leads to an inflow reduction, the reduced water availability can only be mitigated by increased rainfall. Other implications for future climate change are discussed.