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Extreme hot spells can have significant impacts on human society and ecosystems, and therefore it is important to assess how these extreme events will evolve in a changing climate. In this study, the impact of climate change on hot days, hot spells, and heat waves, over 10 climatic regions covering Canada, based on 11 regional climate model (RCM) simulations from the North American Regional Climate Change Assessment Program for the June to August summer period is presented. These simulations were produced with six RCMs driven by four Atmosphere-Ocean General Circulation Models (AOGCM), for the A2 emission scenario, for the current 1970-1999 and future 2040-2069 periods. Two types of hot days, namely HD-1 and HD-2, defined respectively as days with only daily maximum temperature (Tmax) and both Tmax and daily minimum temperature (Tmin) exceeding their respective thresholds (i.e., period-of-record 90th percentile of Tmax and Tmin values), are considered in the study. Analogous to these hot days, two types of hot spells, namely HS-1 and HS-2, are identified as spells of consecutive HD-1 and HD-2 type hot days. In the study, heat waves are defined as periods of three or more consecutive days, with Tmax above 32 °C threshold. Results suggest future increases in the number of both types of hot days and hot spell events for the 10 climatic regions considered. However, the projected changes show high spatial variability and are highly dependent on the RCM and driving AOGCM combination. Extreme hot spell events such as HS-2 type hot spells of longer duration are expected to experience relatively larger increases compared to hot spells of moderate duration, implying considerable heat related environmental and health risks. Regionally, the Great Lakes, West Coast, Northern Plains, and Maritimes regions are found to be more affected due to increases in the frequency and severity of hot spells and/or heat wave characteristics, requiring more in depth studies for these regions to facilitate appropriate adaptation measures. [ABSTRACT FROM AUTHOR]

During the 1970s, Laguna Mar Chiquita (Argentina) experienced a dramatic hydroclimatic anomaly, with a substantial rise in its level. Precipitations are the dominant driving factor in lake level fluctuations. The present study investigates the potential role of remote forcing through global sea surface temperature (SST) fields in modulating recent hydroclimatic variability in Southeastern South America and especially over the Laguna Mar Chiquita region. Daily precipitation and temperature are extracted from a multi-member LMDz atmospheric general circulation model (AGCM) ensemble of simulations forced by HadISST1 observed time-varying global SST and sea-ice boundary conditions from 1950 to 2005. The various members of the ensemble are only different in their atmospheric initial conditions. Statistical downscaling (SD) is used to adjust precipitation and temperature from LMDz ensemble mean at the station scale over the basin. A coupled basin-lake hydrological model ( cpHM) is then using the LMDz-downscaled (LMDz-SD) climate variables as input to simulate the lake behavior. The results indicate that the long-term lake level trend is fairly well depicted by the LMDz-SD- cpHM simulations. The 1970s level rise and high-level conditions are generally well captured in timing and in magnitude when SST-forced AGCM-SD variables are used to drive the cpHM. As the LMDz simulations are forced solely with the observed sea surface conditions, the global SST seems to have an influence on the lake level variations of Laguna Mar Chiquita. As well, this study shows that the AGCM-SD- cpHM model chain is a useful approach for evaluating long-term lake level fluctuations in response to the projected climate changes. [ABSTRACT FROM AUTHOR]

ABSTRACT Spatial structures of hourly precipitation fields were studied from three simulations of the Canadian Regional Climate Model ( CRCM) and observations of the National Centers for Environmental Prediction ( NCEP) Stage IV analysis. Each precipitation structure, defined as a contiguous area of precipitation above a given threshold, was analysed through geometric characteristics (position, area, major and minor axes, eccentricity, orientation) and intensity characteristics (volume, mean and maximum intensities, precipitation distribution within the structure) for 16 climatic regions covering North America. While providing new insights on the spatial facet of precipitation, this study aimed to: (1) assess the performance of the CRCM to reproduce observed precipitation structures and (2) analyse the changes in precipitation structures between historical (1961-1990) and future (2071-2100) periods. In addition, the effect of internal variability was investigated using two CGCM-driven CRCM simulations. In order to assess the CRCM performance, a reanalysis-driven CRCM simulation was first compared with observations and then with CGCM-driven CRCM simulations. Results suggest that reanalysis-driven CRCM precipitation structures displayed intensities spatially more homogeneous than observed ones for the central and eastern United States and showed significantly lower precipitation volumes, intensities and areas. However, annual cycles of characteristic values were well reproduced. In addition, CGCM-driven CRCM showed significantly lower precipitation volumes and intensities during summer months for southeastern regions when compared to reanalysis-driven CRCM. Precipitation structures were also larger and shifted further north. Boundary conditions seemed to influence mainly central and eastern regions of North America. In future climate, results suggest more convective summer precipitations for central and eastern regions (increases in volumes, intensities and heterogeneity of structures), drier spring and summer conditions for southwestern regions (decreases in numbers of structures), wetter winter and spring conditions for northern regions (increases in numbers of structures) and wetter autumn conditions for southeastern regions (increases in volumes and intensities). [ABSTRACT FROM AUTHOR]