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For example, an increase in precipitation in time does not necessarily imply an increase in river water availability-if accompanied by a steep increase in evaporation by more thermal energy availability, runoff can in fact decrease. Although absolute hydroclimatic variables and their changes are interrelated by the conservation of water mass and energy, their magnitude of change may not be consistent. In general, ‘wetter’ implies an increase in water fluxes such as precipitation and runoff or in water stocks such as soil moisture and surface water volume, while ‘drier’ implies the opposite. For example if a given yearly amount of precipitation is confined to only winter months (i.e., snow during dormant season), it has very different implications for the ecosystem compared to if it would fall during summer (i.e., rain during growing season), or within only a few days (i.e., extreme weather events). So it is not only the overall amount of a variable that matters, but also its spatial and temporal distribution. large-scale), but also temporally (e.g., long-term totals vs. Moreover, hydroclimatic patterns vary not only spatially (e.g., ocean vs. It is worth noting that the ‘dry gets drier, wet gets wetter’ paradigm is mostly based on oceanic data and apparently does not hold for changes over land. However, confusion appears to be arising within the multidisciplinary climate change community because of the inconsistent use of the terms ‘wetter’ and ‘drier’ to describe changes in a broad range of hydroclimatic trends and their effects on ecosystems, agriculture, and water supply for societies. On the contrary, an estimate of potentially wetter conditions appears to reduce the threat of expected catastrophic droughts, but can raise concern and awareness in the population to experience more flooding events and intense rains. An estimate of potentially drier conditions would motivate authorities to prepare for drought and reductions in the freshwater resource required for private households, industry, energy and agriculture sectors. Predictions of drier or wetter conditions should be communicated carefully and accurately both among scientists and to the public, especially to stakeholders and populations who depend directly on that water resource. Hence, the terms ‘drier’ and ‘wetter’ are now used widely across disciplines, with studies describing historical or future changes in water availability. This question is also related to the paradigm ‘dry gets drier, wet gets wetter’, agreeing with the general concept of the intensification of the water cycle. One of the main questions in climate change studies therefore is whether a specific region will increase or decrease its amount of water.

Such hydrological changes can affect society either directly, e.g., through catastrophic damage, or indirectly, e.g., through reduced crop productivity. For example, reduced precipitation can cause droughts, higher temperatures can turn snowfall into rainfall, and increased runoff can lead to floods. In this way, we hope that the terms ‘wetter’ and ‘drier’ used in scientific studies are easier to relate to hydroclimatic processes, which should facilitate the application by authorities and policy makers.Ĭlimate change-induced alterations of the global hydrological cycle can have substantial impacts on local climate, ecosystems, and societies. In order to facilitate meta-analyses across disciplines, we therefore highlight the need to explicitly state which hydroclimatic variables authors are referring to. Some studies do not define the terms at all. We found that although precipitation is prevalently used to describe ‘wetter’ and ‘drier’ conditions, many other variables are also used to refer to changes in water availability between research fields, pointing to a varied perspective on the use of these terms. We conducted a literature review of almost 500 recent climate change studies to quantitatively investigate the consistency of the use of these terms across disciplines, regarding the hydroclimatic variables they are related to. In terrestrial ecosystems, these changes are usually described with the terms ‘wetter’ and ‘drier’, which refer to the change in the quantity and/or presence of water, either as water fluxes or stocks.

Ongoing and future hydroclimatic changes have large environmental and societal impacts.