No abstract

[1] Thirty-three snowpack models of varying complexity and purpose were evaluated across a wide range of hydrometeorological and forest canopy conditions at five Northern Hemisphere locations, for up to two winter snow seasons. Modeled estimates of snow water equivalent (SWE) or depth were compared to observations at forest and open sites at each location. Precipitation phase and duration of above-freezing air temperatures are shown to be major influences on divergence and convergence of modeled estimates of the subcanopy snowpack. When models are considered collectively at all locations, comparisons with observations show that it is harder to model SWE at forested sites than open sites. There is no universal ''best'' model for all sites or locations, but comparison of the consistency of individual model performances relative to one another at different sites (and vice versa). Calibration of models at forest sites provides lower errors than uncalibrated models at three out of four locations. However, benefits of calibration do not translate to subsequent years, and benefits gained by models calibrated for forest snow processes are not translated to open conditions.

River floods are among some of the costliest natural disasters [1], but their socioeconomic impacts under contrasting warming levels remain little explored [2]. Here, using a multi-model framework, we estimate human losses, direct economic damage, and subsequent indirect impacts (welfare losses) under a range of temperature (1.5°C, 2°C, and 3°C [3]) and socioeconomic scenarios, assuming current vulnerability levels and in absence of future adaptation. At 1.5°C, depending on the socioeconomic scenario, it is found that human losses from flooding could rise by 70 to 83%, direct flood damage by 160 to 240%, with a relative welfare reduction between 0.23 to 0.29%. In a 2°C world, by contrast, the death toll is 50% higher, direct economic damage doubles, and welfare losses grow to 0.4%. Impacts are notably higher under 3C warming, but at the same time, variability between ensemble members also increases, leading to greater uncertainty regarding flood impacts at higher warming levels. Flood impacts are further shown to have uneven regional distribution, with greatest losses observed over the Asian continent at all specific warming levels. It is clear that increased adaptation and mitigation effortsperhaps through infrastructural investment [4]is needed to offset increasing river flood risk in the future.

Simulated daily discharge derived from a relatively high-resolution (approximately 1.1-degree) general circulation model was used to investigate future projections of extremes in river discharge under global warming. The frequency of floods was projected to increase over many regions, except those including North America and central to western Eurasia. The drought frequency was projected to increase globally, while regions such as northern high latitudes, eastern Australia, and eastern Eurasia showed a decrease or no significant changes. Changes in flood and drought are not explained simply by changes in annual precipitation, heavy precipitation, or differences between precipitation and evapotranspiration. Several regions were projected to have increases in both flood frequency and drought frequency. Such regions show a decrease in the number of precipitation days, but an increase in days with heavy rain. Several regions show shifts in the flood season from springtime snowmelt to the summer period of heavy precipitation.Key words drought; flood; global warming; river discharge Projections globales des changements dans les risques de crues et de sécheresses liés au changement climatiqueRésumé Les débits journaliers simulés à partir d'un modèle de circulation générale d'une résolution relativement haute (approximativement 1.1 degré) ont été utilisés pour étudier les projections futures des extrêmes des débits de rivières dans le contexte du réchauffement global. Une augmentation de la fréquence des crues est projetée pour de nombreuses régions, à l'exception des régions incluant l'Amérique du Nord et l'Eurasie centrale à occidentale. L'augmentation de la fréquence des sécheresses est projetée globalement, alors que les régions des hautes latitudes boréales, de l'Australie orientale et de l'Eurasie orientale présentent une décroissance ou une absence de changement significatif. Les changements pour les crues et les sécheresses ne s'expliquent pas simplement par des changements dans les précipitations annuelles, les fortes précipitations ou les différences entre précipitation et évapotranspiration. Les projections de plusieurs régions présentent des augmentations à la fois dans la fréquence des crues et dans celle des sécheresses. De telles régions présentent une décroissance dans le nombre de jours de précipitation, mais une augmentation des jours de forte précipitation. Plusieurs régions présentent des décalages de la saison des crues, de la période printanière de fonte nivale vers la période estivale de fortes précipitations.