Looking Up or Looking Down? Hydrologic and Atmospheric Perspectives on Precipitation and Evaporation Variability.

Precipitation and evapotranspiration, respectively, an input and an output for hydrologists and ocean scientists, but the opposite for meteorologists, quantify the intensity of vertical water exchange between land, ocean, and the atmosphere. The interesting paper by Dagan et al. (2019, https://doi.org/10.1029/2019GL084173) analyzed important constraints between such fluxes as a function of spatial scales. This commentary aims to provide a complementary, hydrologic point of view, emphasizing how their intermittency at different spatial and temporal scales is essentially related to the contrasting water storage capacities of the atmosphere and the Earth's surface. Alterations of such storage due to global warming and land cover change are a challenge for the geophysical community and beyond. Plain Language Summary: With the common goal of understanding the water cycle, hydrologists look up at the atmosphere and consider precipitation as an input, whereas meteorologists look down at the surface and think of precipitation as an output. These two perspectives on water cycle result in two distinctive yet closely related approaches, focusing on the land surface and the atmosphere, respectively. These dynamics are expected to change in response to the global warming and land use land cover change, increasing the uncertainties of predicting intense droughts and floods. Collaborative research efforts are needed to improve our understanding of the water cycle and mitigate such effects. Key Points: We add a hydrologic perspective to Dagan et al.'s atmospheric perspective on precipitation and evaporation differencesWe discuss the spatial/temporal scaling constraints imposed by the surface hydrologic cycleThese scaling properties are related to the water storage capacities in the land and atmosphere, both of which are expected to change [ABSTRACT FROM AUTHOR]