Nobuyuki Utsumi

Projection of future world water resources under SRES scenarios: water withdrawal

Abstract Potential changes in the availability of water resources are one of the greatest concerns relating to global climate warming. Socio-economic developments will also influence water use and demands. This study was conducted to evaluate potential changes in water withdrawals and availability under various socio-economic and climate change scenarios. In the current paper, which presents the first part of the study, future potential water withdrawals are projected according to socio-economic driving factors under the scenarios A1b, A2, B1, and B2 of the Special Report on Emission Scenarios (SRES), which was released for the Fourth Assessment Report on global warming by the Intergovernmental Panel on Climate Change (IPCC-AR4) in 2000. Total world water withdrawal is currently approximately 3800 km3/year, and will likely exceed 6000 km3/year by 2055, according to all scenarios. Water withdrawal is projected to increase in the future, but change trends largely depend on the socio-economic scenarios. Scenario A2 shows the extreme situation of continuously increasing water withdrawal. The scenario with global cooperation on solutions to social, economic, and environmental issues (Scenario B1) illustrates that society can reach relatively higher economic development by using less water and thus encourages sustainable governance of world water resources. In addition, comparison with other studies is conducted to help us understand the uncertainty range when projecting world water withdrawals according to different methods and assumptions.

Projection of future world water resources under SRES scenarios: an integrated assessment

Abstract Changes in water resources availability, as affected by global climate warming, together with changes in water withdrawal, could influence the world water resources stress situation. In this study, we investigate how the world water resources situation will likely change under the Special Report on Emissions Scenarios (SRES) by integrating water withdrawal projections. First, the potential changes in water resources availability are investigated by a multi-model analysis of the ensemble outputs of six general circulation models (GCMs) from organizations worldwide. The analysis suggests that, while climate warming might increase water resources availability to human society, there is a large discrepancy in the size of the water resource depending on the GCM used. Secondly, the changes in water-stressed basins and the number of people living in them are evaluated by two indices at the basin scale. The numbers were projected to increase in the future and possibly to be doubled in the 2050s for the three SRES scenarios A1b, A2 and B1. Finally, the relative impacts of population growth, water use change and climate warming on world water resources are investigated using the global highly water-stressed population as an overall indicator. The results suggest that population and socio-economic development are the major drivers of growing world water resources stress. Even though water availability was projected to increase under different warming scenarios, the reduction of world water stress is very limited. The principal alternative to sustainable governance of world water resources is to improve water-use efficiency globally by effectively reducing net water withdrawal. Editor Z.W. Kundzewicz; Associate editor D. Gerten

Which weather systems are projected to cause future changes in mean and extreme precipitation in CMIP5 simulations

Future changes in precipitation due to climate change are of great concern to society. However, questions such as “Which weather systems will cause which changes?” and “Is the relative importance of these weather systems likely to change in the future?” have not been addressed fully yet. Here, we present the first global estimates of the relative contributions of different weather systems (i.e., tropical cyclones, extratropical cyclones including fronts, and others) to changes in annual mean and extreme precipitation in the late 21st century using multi-model projections of the Coupled Model Intercomparison Project Phase 5. Although the models present biases in tropical cyclones over southern hemisphere in particular, the representations of global weather system patterns are comparable to the reanalysis data. Total precipitation from tropical cyclones decreases (increases) in the tropics (subtropics) and that from extratropical cyclones including fronts decreases (increases) on the equatorial (poleward) side of the storm tracks. In addition the mean intensity and frequency of system-wise precipitation can change significantly even without considerable changes in annual amounts. We found that the subtropics, particularly in the Pacific and North Atlantic, are the regions where the proportions of precipitation by weather systems in annual mean and extreme precipitation displays notable changes, suggesting distinct shifts in climate regimes. These regions have a common feature: they undergo the influence of several distinct weather systems in the present climate. In regions where climate regime shifts are projected, even the weather systems that have a minor contribution to precipitation in the present climate may cause considerable changes in annual and extreme precipitation.

Climatological characteristics of fronts in the western North Pacific based on surface weather charts

Composite front climatology in the western North Pacific is determined using a newly developed 1.0° gridded data set. Here we propose a research strategy for determining the spatiotemporal distribution of fronts using weather chart images published by the Japan Meteorological Agency, one of the major data providers in the region. A preliminarily investigation of the internal data characteristics for the period of 2000–2010 is undertaken, and the final 4 years of data are used for an analysis of front climatology to avoid the effect of any spurious trends. This enables in-depth analyses to be conducted, which have not previously been possible in the region, including the composites of cross-sectional patterns for the thermal fields and precipitation near fronts, front length seasonality, and the significance of the thermal gradient near the fronts, in addition to determining the frontal frequency and spatial distribution of frontal precipitation. Pixel-wise analysis reveals that 56% of the local precipitation maximum is located on the warm side of a cold front caused by less tilted upward motion on the warm side, with the intrusion of the upper level cold dry air into the warm side. This new data set also enables a further analysis of the occluded fronts, which are not correctly distinguished in the existing objective detection method.

Relative contributions of weather systems to mean and extreme global precipitation

This study presents the first global estimates of the relative contributions of different weather systems, i.e. tropical cyclone, center and front of extratropical cyclone, and others, to mean and extreme precipitation. An objective method of classification of the precipitating weather systems was used with a reanalysis dataset and a satellite-based precipitation product for 2001–2010. Tropical cyclones, extratropical cyclones with associated fronts, and other weather systems contribute about 4%, 37%, and 59%, respectively, of the global (60°S–60°N) mean precipitation. The relative contributions of the weather systems were found to be different both in terms of the different classes of precipitation intensity and in terms of the different temporal scales of precipitation. Tropical cyclones and extratropical cyclones produced greater contributions to extreme hourly precipitation than to annual precipitation in most of the oceanic regions of their activity. The contributions of tropical cyclones to extreme precipitation showed clear peaks on temporal scales of 24–72 hours. The contributions of extratropical cyclones showed less dependence on the temporal scale than tropical cyclones. Consideration of combinations of multiple weather systems revealed that in eastern North America and East Asia, substantial portions (22% and 19%, respectively) of the extreme 24-hour precipitation related to tropical cyclones are contributed by the coexistence of tropical cyclones and fronts. However, such contributions were found rarely in other land regions. On most temporal scales, fronts at locations remote from the centers of extratropical cyclones were found to contribute to extreme precipitation as much as the centers of extratropical cyclones.