Weather Research and Forecasting (WRF) model simulations are performed over Russia for July and December 2005, 2006 to create a ''dataset'' to assess the impact of network density and design on regional averages. Based on the values at all WRF grid points, regional averages for various quantities are calculated for 2.88 3 2.88 areas as the ''reference.'' Regional averages determined based on 40 artificial networks and 411 ''sites'' that correspond to the locations of a real network are compared with the reference regional averages. The 40 networks encompass 10 networks of 500, 400, 200, or 100 different randomly taken WRF grid points as sites. The real network's site distribution misrepresents the landscape. This misrepresentation leads to errors in regional averages that show geographical and temporal trends for most quantities: errors are lower over shores of large lakes than coasts and lowest over flatland followed by low and high mountain ranges; offsets in timing occur during frontal passages when several sites are passed at nearly the same time. Generally, the real network underestimates regional averages of sea level pressure, wind speed, and precipitation over Russia up to 4.8 hPa (4.8 hPa), 0.7 m s 21 (0.5 m s 21 ), and 0.2 mm day 21 and overestimates regional averages of 2-m temperature, downward shortwave radiation, and soil temperature over Russia up to 1.9 K (1.4 K), 19 W m 22 (14 W m 22 ), and 1.5 K (1.8 K) in July (December). The low density of the ten 100-site networks causes difficulties for sea level pressure. Regional averages obtained from the 30 networks with 200 or more randomly distributed sites represent the reference regional averages, trends, and variability for all quantities well.
ABSTRACT:The Canadian Prairies have experienced severe and extended droughts that have had significant impacts on agriculture, energy and other socio-economic sectors; it is therefore desirable to assess future changes to drought characteristics in this drought prone region, in the context of a changing climate. This study addresses validation and projected changes to short-and long-term drought characteristics, i.e. severity, frequency and duration, over the Canadian Prairies, using an ensemble of ten Canadian RCM (CRCM) simulations, of which five correspond to the current 1971-2000 period and the other five are the matching simulations for the future 2041-2070 period. These five pairs of current and future CRCM simulations were driven by five different members of a Canadian Global Climate Model ensemble. Validation of CRCM simulated precipitation suggests that the model reproduces the observed precipitation distribution for all seasons, except summer, across a large portion of the Canadian Prairies. However, comparison of CRCM simulated drought characteristics with those observed suggests that the model has difficulties in reproducing observed severity, frequency and duration of drought events, particularly those associated with longer events, possibly due to the overestimation of summer precipitation by the model. Analysis of projected changes to precipitation and drought characteristics between the 1971-2000 and 2041-2070 periods suggests a decrease in mean precipitation in summer and an increase for the other seasons, while the severity, frequency and maximum duration of both short-and long-term droughts are projected to increase over the southern Prairies, with the largest projected changes associated with longer drought events. Classification of the watersheds spanning the southern Prairies based on changes to both severity and frequency further reveal the vulnerability of this region in a changing climate.
An index of North Atlantic tropical cyclone (TC) damage potential due to winds and coastal surge is developed using seasonal climate variables of relative sea surface temperature and steering flow. These climate variables are proxies for the key damaging TC parameters of intensity, size, and forward speed that constitute an existing cyclone damage potential index. This climate-based approach has the advantage of sidestepping the need for data on individual TCs and explains 48 % of the variance in historical cyclone damage potential. The merit of the cyclone damage potential is in assessments relative to past events or past periods, and may be translated to actual damage using relationships between the damage potential index and specific exposure and vulnerability characteristics. Spread in the change in damage potential over the 21st century among climate simulations under representative concentration pathways 4.5, 6.0, and 8.5 is found to be less than the spread due to internal variability, as assessed using a climate model initial condition large ensemble. This study highlights the importance of accounting for internal climate variability in future climate impact assessments.
The 2012 drought was the most severe and extensive summertime U.S. drought in half a century with substantial economic loss and impacts on food security and commodity prices. A unique aspect of the 2012 drought was its rapid onset and intensification over the Southern Rockies, extending to the Great Plains during late spring and early summer, and the absence of known precursor large‐scale patterns. Drought prediction therefore remains a major challenge. This study evaluates relationships among snow, soil moisture, and precipitation to identify sources of potential predictability of the 2012 summer drought using observations and a Weather Research and Forecasting model multiphysics ensemble experiment. Although underestimated in intensity, the drought signal is robust to the way atmospheric physical processes are represented in the model. For the Southern Rockies, soil moisture exhibits stronger persistence than precipitation in observations and the ensemble experiment. Correlations between winter/spring snowmelt and concurrent and following season soil moisture, and between soil moisture and concurrent and following season precipitation, in both observations and the model ensemble, suggest potential predictability beyond 1 and 2 month lead‐time reside in the land surface conditions for apparent flash droughts such as the 2012 drought.
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