CLIMATE CHANGE AND DROUGHT (Q FU, SECTION EDITOR) Climate Change and Drought: the Soil Moisture Perspective Alexis Berg 1 & Justin Sheffield 2 # Springer International Publishing AG, part of Springer Nature 2018 Abstract Purpose of review We review the extensive and sometimes conflicting recent literature on drought changes under global warming. We focus on soil moisture deficits, which are indicative of associated impacts on ecosystems. Soil moisture is a key state variable of the land surface, reflecting complex interactions between the water, energy, and carbon cycles. Recent findings Offline projections relying on soil moisture proxy metrics indicate dramatic future drought increases, often interpreted as primarily driven by warming-induced increases in evaporative demand. However, such results appear inconsistent with other trends in the land–atmosphere system, including soil moisture, vegetation, and evapotranspiration. Recent studies begin to explain these discrepancies, highlighting the importance of soil–vegetation–atmosphere coupling, unaccounted for in offline projections. Summary Future changes in soil moisture droughts should preferably be assessed with prognostic model outputs rather than offline heuristics and be interpreted in the context of the coupled soil–vegetation–atmosphere system. Keywords Drought . Climate change . Soil moisture Introduction Drought is an anomalous lack of water at the land–atmo- sphere interface. It begins with a reduction of precipitation (known as meteorological drought) and can propagate, as it persists, into soil moisture (agricultural drought) and stream flow, lake levels, and groundwater (hydrological drought). Drought can have huge impacts on all aspects of human activities, including water resources, agricultural production, energy generation, and industrial output. For example, the recent drought in California caused $2.2B in losses with agricultural losses alone of $810M [1] and led to multiple further effects, such as on water restrictions [2] and land subsidence [3]. Drought also has large impacts on ecosystems, contributing to, for example, tree die-off [4]. In the developing world, where livelihoods are dependent on agriculture, drought can have devastating impacts, lead- ing to famine, migration, and potential conflict [5–7]. As a result, the potential for increasing drought severity, and more generally, a shift in the mean level of aridity over land, is perhaps one of the more concerning possible con- sequences of global warming. We generally have a good understanding of the drivers of meteorological drought variability, that is, a combina- tion of sea surface temperature variability and land–atmo- sphere feedbacks, in addition to random, and unpredict- able, weather fluctuations [8–10]. With climate change, it is expected that this will continue; but as the global cli- mate system changes, drought risk will be altered by the interaction of mean changes with changes in variability and land–atmosphere feedbacks. These potential alter- ations and related trends have been the focus of numerous articles since the 1990s and have been increasingly discussed by Intergovernmental Panel on Climate Change (IPCC) reports beginning with the third assess- ment report [11]. While the last IPCC report [12] indicates that current global trends in droughts are uncertain, it indicates likely increases in regional drought in the future based on climate model projections. In addition, in recent This article is part of the Topical Collection on Climate Change and Drought * Alexis Berg ab5@princeton.edu 1 Department of Civil and Environmental Engineering, Princeton University, Princeton, NJ, USA 2 Geography and Environment, University of Southampton, Southampton, UK Current Climate Change Reports https://doi.org/10.1007/s40641-018-0095-0