Hydrological droughts in the 21st century, hotspots and uncertainties from a global multimodel ensemble experiment

Abstract

Increasing concentrations of greenhouse gases in the atmosphere are expected to modify the global water cycle with significant consequences for terrestrial hydrology. We assess the impact of climate change on hydrological droughts in a multimodel experiment including seven global impact models (GIMs) driven by biascorrected climate from five global climate models under four representative concentration pathways (RCPs). Drought severity is defined as the fraction of land under drought conditions. Results show a likely increase in the global severity of hydrological drought at the end of the 21st century, with systematically greater increases for RCPs describing stronger radiative forcings. Under RCP8.5, droughts exceeding 40% of analyzed land area are projected by nearly half of the simulations. This increase in drought severity has a strong signal-to-noise ratio at the global scale, and Southern Europe, the Middle East, the Southeast United States, Chile, and South West Australia are identified as possible hotspots for future water security issues. The uncertainty due to GIMs is greater than that from global climate models, particularly if including a GIM that accounts for the dynamic response of plants to CO 2 and climate, as this model simulates little or no increase in drought frequency. Our study demonstrates that different representations of terrestrial water-cycle processes in GIMs are responsible for a much larger uncertainty in the response of hydrological drought to climate change than previously thought. When assessing the impact of climate change on hydrology, it is therefore critical to consider a diverse range of GIMs to better capture the uncertainty.climate impact | global hydrology | evaporation | global warming T he global water cycle is expected to change over the 21st century due to the combined effects of climate change and increasing human intervention. In a warmer world, the waterholding capacity of the atmosphere will increase, resulting in a change in the frequency of precipitation extremes, increased evaporation and dry periods (1), and intensification of droughts (2). This process is represented by most global climate models (GCMs) by increased summer dryness and winter wetness over large areas of continental mid to high latitudes in the Northern Hemisphere (3), associated with a reduction in water availability at continental (4, 5) and global scales (6, 7). Because such changes have potentially very serious implications in some regions of the world, identifying areas where there is agreement in the direction and magnitude of changes in drought characteristics (hotspots) in response to climate change is essential information for water resource management aimed at ensuring water security in a changing climate.Most GCMs, however, are not able to reproduce the fine-scale processes governing terrestrial hydrology (and hence runoff) and suffer from systematic biases (8). As land-atmospheric feedbacks are not yet fully understood and reproduced by global models (9), and because full coupling ...

Future discharge drought across climate regions around the world modelled with a synthetic hydrological modelling approach forced by three general circulation models

“…They showed that largest uncertainty in the projections of future hydrological drought is found in the temperate climate and this uncertainty is mainly caused by the uncertainty in the GHMs. This large uncertainty in the GHMs was also found by Prudhomme et al (2014) for the CMIP5 climate projections in the ISI-MIP project. Prudhomme et al (2014) compared a large ensemble of GCM-GHM combinations and showed that the highest projection uncertainty could be related to the GHM runoff-generating processeswhich is supported by the work of Haddeland et al (2011) and Hagemann et al (2013).…”

“…This large uncertainty in the GHMs was also found by Prudhomme et al (2014) for the CMIP5 climate projections in the ISI-MIP project. Prudhomme et al (2014) compared a large ensemble of GCM-GHM combinations and showed that the highest projection uncertainty could be related to the GHM runoff-generating processeswhich is supported by the work of Haddeland et al (2011) and Hagemann et al (2013). It was found by Alderlieste et al (2014) that the change in the projected characteristics of future drought is larger (climate signal) than the uncertainty in the GCM-GHM combinations.…”

“…The number and spatial distribution of drought events did not clearly show a consistent change. As part of the ISI-MIP project, Prudhomme et al (2014) used an ensemble of GCM-GHM combinations and found that drought occurrence will increase globally with the exception of the snow-dominated regions. Strong increases in drought occurrence are found for the Mediterranean region, which is confirmed by this study.…”

“…Moreover, the impact of GHMs on future drought projections is significant (e.g. Haddeland et al, 2011;Van Huijgevoort et al, 2014;Prudhomme et al, 2014), which makes a detailed impact assessment of the importance of climate and catchment structure even more complicated. To investigate the relative importance of climate and catchment structure on hydrological drought, used a synthetic hydrological modelling approach to study the effects of these factors on hydrological drought characteristics on a global scale.…”

“…In that sense, it adds to the few existing impact studies (e.g. Prudhomme et al, 2014). However, we add to these studies by elaborating the projected hydrological drought in more depth: (i) distribution of different drought characteristics over major climates (e.g.…”