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This study investigates the role of large-scale and local-scale processes associated with heat waves using two reanalysis products, and evaluates the performance of the regional climate model ensemble used in the North America Regional Climate Change Program (NARCCAP) in reproducing these processes. The Continental US is divided into eight different climate divisions to investigate different mechanisms associated with heat waves. At the large scale, heat waves are associated with terrestrial warm air advection to the Northeast, Midwest and Northern Great Plains, and with oceanic warm air advection for the Southeast and Southern Great Plains. Over the western US, reduced maritime cool air advection results in local warming. At the local scale, antecedent precipitation deficits lead to the continuous drying of soil, more net radiative energy is partitioned into sensible heat flux and acts to warm surface air temperature, especially over the Great Plains. NARCCAP-simulated large-scale meteorological patterns and temporal evolution of antecedent local scale terrestrial conditions are shown to be very similar to those of the reanalysis products. Even though extreme temperature is overestimated by the NARCCAP ensemble over the US, different heat wave metrics are realistically represented both in terms of the inter-annual variability and spatial representation. However, NARCCAP overestimates the magnitude of heatwaves over the Northeast, Midwest and Northern Great Plains, partially due to anomalous heat advection through large-scale forcing. [ABSTRACT FROM AUTHOR]

Transitions to terrestrial ecosystems attributable to land cover and land use change (LCLUC) and climate change can affect the climate at local to regional scales. However, conclusions from most previous studies do not provide information about local climate effects, and little research has directly quantified how LCLUC intensity within different ecoregions relates to climate variation. In this study, we present an observation-based analysis of climate sensitivity to LCLUC based on decadal LCLUC and climate data in different ecoregions. Our results revealed that variations in land surface temperature and vapor pressure were most sensitive to LCLUC across the conterminous United States, while precipitation was less sensitive. Persistent warming effects were produced from LCLUC in Appalachian and some of the central U.S., High Plains, and northwest ecoregions, but cooling effects were evident in the many southeast, northeast and some Great Lakes and Intermountain West ecoregions. Most of the warming and a few cooling ecoregions were sensitive to LCLUC. Ecoregions with increasing vapor pressure were found across the Great Plains, Intermountain West, and West Coast ecoregions and several of these regions in the Great Plains and West Coast were sensitive to LCLUC. A combination of changes in temperature, precipitation, and vapor pressure was used to characterize climate sensitivity associated with LCLUC forcing, and five major persistent patterns were found in some ecoregions. These findings suggest that climate conditions, especially temperature and vapor pressure, in some ecoregions are sensitive to LCLUC and such change should be better incorporated into regional climate assessments. • Decadal land cover and land use change (LCLUC) data has been analyzed to reveal change intensity. • Climatic sensitivity to land cover and land use change forcing has been performed. • Variations in land surface temperature and vapor pressure are relatively more sensitive to land cover and land use change than precipitation. • More warming ecoregions are sensitive than those of cooling ecoregions. • Accounting for regional changes in climate induced by LCLUC is important for climate change assessments [ABSTRACT FROM AUTHOR]