Global Distribution of Climatic Aridity

Aridity exerts fundamental controls on terrestrial hydrology with impacts on ecosystems and society. Here we show that the global distribution of dryness index is dominated by the exponential variability of precipitation. The resulting distribution of the dryness index only has one parameter describing the balance between global mean atmospheric water demand and supply. Its shape, with a minus two power-law tail, is well supported by observations and appears to be robust to future changes in aridity, making it a possible benchmark for Earth System Models.