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[en] Regional climate models (RCMs) have been used to dynamically downscale global climate projections at high spatial and temporal resolution in order to analyse the atmospheric water cycle. In southern Africa, precipitation pattern were strongly affected by the moisture transport from the southeast Atlantic and southwest Indian Ocean and, consequently, by their sea surface temperatures (SSTs). However, global ocean models often have deficiencies in resolving regional to local scale ocean currents, e.g. in ocean areas offshore the South African continent. By downscaling global climate projections using RCMs, the biased SSTs from the global forcing data were introduced to the RCMs and affected the results of regional climate projections. In this work, the impact of the SST bias correction on precipitation, evaporation and moisture transport were analysed over southern Africa. For this analysis, several experiments were conducted with the regional climate model REMO using corrected and uncorrected SSTs. In these experiments, a global MPI-ESM-LR historical simulation was downscaled with the regional climate model REMO to a high spatial resolution of 50 × 50 km2 and of 25 × 25 km2 for southern Africa using a double-nesting method. The results showed a distinct impact of the corrected SST on the moisture transport, the meridional vertical circulation and on the precipitation pattern in southern Africa. Furthermore, it was found that the experiment with the corrected SST led to a reduction of the wet bias over southern Africa and to a better agreement with observations as without SST bias corrections.
[en] The book on the climatic change in Germany includes contributions to the following issues: global climate projections and regional projections in Germany and Europe: observation of the climatic change in Central Europe, regional climate modeling, limits and challenges of the regional climate modeling; climatic change in Germany - regional features and extremes: temperature and heat waves, precipitation, wind and cyclones, sea-level increase, tides, storm floods and sea state, floods, definition uncertainties, draughts, forest fires, natural risks; consequences of the climatic change in Germany: air quality, health, biodiversity, water resources, biochemical cycles, agriculture, forestry, soils, personal and commercial transport, cities and urban regions, tourism, infrastructure, energy and water supplies, cost of the climatic change and economic consequences; overall risks and uncertainties: assessment of vulnerabilities, literature review, climatic change as risk enhancement in complex systems, overall risks and uncertainties, decision making under uncertainties in complex systems; integrated strategies for the adaptation to the climatic change: the climate resilient society - transformations and system changes, adaptation to the climatic change as new political field, options for adaptation strategies.
[en] Dry years and dry summers in Hungary have been analyzed using the regional climate model REMO for the time periods 1961-2000 and 2001-2100. Dry periods were determined and classified by intensity, considering modeled and observed precipitation and temperature data. The intensity of dry events was defined according to the negative precipitation deviation and positive temperature deviation from the climate period 1961-90. The proportion of dry years and dry summers is equivalent in the model and observations in the past. On average, the intensity of dry years simulated by the regional climate model REMO is the same as observed, whereas dry summers have more extreme conditions in the model. Based on the results of three IPCC scenario simulations (B1, A1B, A2), the probability of dry events will be higher in the second half of the 21st century. In the scenarios A1B and A2 a dry summer may happen every second year and the consecutive dry periods will last longer. For 2051-2100 the intensity of dry events increases significantly in all scenarios compared to the control period. From the analyzed scenarios B1 has the lowest future greenhouse gas emission rates, so that the smallest changes are also projected for the second half of the 21st century
[en] Climatic effects of forest cover change have been investigated for Hungary. For the time period 2071–100 we have analyzed whether the climate change signal for summer precipitation and the probability of droughts can be reduced assuming maximal afforestation for the entire country (forests covering all vegetated areas). The biogeophysical effects of land cover change have been assessed using the results of an A1B IPCC-SRES emission scenario from REMO (regional climate model at the Max Planck Institute for Meteorology, Hamburg). The simulation results indicate that afforestation may reduce the projected climate change through higher evapotranspiration and precipitation as well as lower surface temperature for the entire summer period. The magnitude of the feedback of the forest cover increase on precipitation differs among regions. The strongest effects are visible in the northeastern part of the country. Here, half of the projected precipitation decrease can be relieved and the total number of drought events can be reduced, assuming maximal afforestation. Afforestation brings about the smallest climatic effect in the southwestern region, in the area that shows the strongest climate change. The results can help to identify areas where forest cover increase should most effectively support the alleviation of climate change effects.
[en] A new high-resolution regional climate change ensemble has been established for Europe within the World Climate Research Program Coordinated Regional Down-scaling Experiment (EURO-CORDEX) initiative. The first set of simulations with a horizontal resolution of 12.5 km was completed for the new emission scenarios RCP4.5 and RCP8.5 with more simulations expected to follow. The aim of this paper is to present this data set to the different communities active in regional climate modelling, impact assessment and adaptation. The EURO-CORDEX ensemble results have been compared to the SRES A1B simulation results achieved within the ENSEMBLES project. The large-scale patterns of changes in mean temperature and precipitation are similar in all three scenarios, but they differ in regional details, which can partly be related to the higher resolution in EURO-CORDEX. The results strengthen those obtained in ENSEMBLES, but need further investigations. The analysis of impact indices shows that for RCP8.5, there is a substantially larger change projected for temperature-based indices than for RCP4.5. The difference is less pronounced for precipitation-based indices. Two effects of the increased resolution can be regarded as an added value of regional climate simulations. Regional climate model simulations provide higher daily precipitation intensities, which are completely missing in the global climate model simulations, and they provide a significantly different climate change of daily precipitation intensities resulting in a smoother shift from weak to moderate and high intensities. (authors)
[en] A global warming of 2 °C relative to pre-industrial climate has been considered as a threshold which society should endeavor to remain below, in order to limit the dangerous effects of anthropogenic climate change. The possible changes in regional climate under this target level of global warming have so far not been investigated in detail. Using an ensemble of 15 regional climate simulations downscaling six transient global climate simulations, we identify the respective time periods corresponding to 2 °C global warming, describe the range of projected changes for the European climate for this level of global warming, and investigate the uncertainty across the multi-model ensemble. Robust changes in mean and extreme temperature, precipitation, winds and surface energy budgets are found based on the ensemble of simulations. The results indicate that most of Europe will experience higher warming than the global average. They also reveal strong distributional patterns across Europe, which will be important in subsequent impact assessments and adaptation responses in different countries and regions. For instance, a North–South (West–East) warming gradient is found for summer (winter) along with a general increase in heavy precipitation and summer extreme temperatures. Tying the ensemble analysis to time periods with a prescribed global temperature change rather than fixed time periods allows for the identification of more robust regional patterns of temperature changes due to removal of some of the uncertainty related to the global models’ climate sensitivity. (paper)
[en] A number of studies have shown that added value is obtained by increasing the horizontal resolution of a regional climate model to capture additional fine-scale weather processes. However, the mechanisms leading to this added value are different over areas with complicated orographic features, such as the Tibetan Plateau (TP). To determine the role that horizontal resolution plays over the TP, a detailed comparison was made between the results from the REMO regional climate model at resolutions of 25 and 50 km for the period 1980–2007. The model was driven at the lateral boundaries by the European Centre for Medium-Range Weather Forecasts Interim Reanalysis data. The experiments differ only in representation of topography, all other land parameters (e.g., vegetation characteristics, soil texture) are the same. The results show that the high-resolution topography affects the regional air circulation near the ground surface around the edge of the TP, which leads to a redistribution of the transport of atmospheric water vapor, especially over the Brahmaputra and Irrawaddy valleys—the main water vapor paths for the southern TP—increasing the amount of atmospheric water vapor transported onto the TP by about 5%. This, in turn, significantly decreases the temperature at 2 m by > 1.5 °C in winter in the high-resolution simulation of the southern TP. The impact of topography on the 2 m temperature over the TP is therefore by influencing the transport of atmospheric water vapor in the main water vapor paths.
[en] The Hengduan Mountains and Tibetan Plateau possess unique topographical characteristics that serve as an effective blocking of the movement of the westerly wind in the middle and lower troposphere towards East China. This study examines results from a regional climate model (REMO) at the resolutions of 25 and 50 km for the period 1980–2012. The model is run using lateral boundary conditions from ERA-Interim (European Centre for Medium-Range Weather Forecasts interim reanalysis). There are only a few differences between 25 and 50 km in land surface/vegetation characteristics, but the major differences in this region are due to the orography. Results show that the high-resolution simulation performance is poor in winter, when southwesterly wind prevails, whereas it performs well in summer, when the westerly wind is substantially weakened in southern China. In comparison to the ERA-Interim wind field, the high-resolution simulation overestimates the air flow over the Hengduan Mountains near the ground surface, which influences the transport of atmospheric water vapor in the downstream region, i.e., over southern China. Specifically, with the help of the overestimated southwesterly wind, the amount of atmospheric water vapor transported increases considerably perennially by up to 20% in southern China, while it decreases remarkably by more than 5% throughout the year in a large area of Central and North China. These features lead to excessive precipitation and underestimated cloud cover in southern China, which probably causes the overestimated 2-m temperature in southern China. Our study emphasizes that, in such high-resolution-model studies for East Asia, special attention should be paid to the near-surface winds over the Hengduan Mountains.
[en] An ensemble of regional climate model (RCM) runs from the EU HighNoon project are used to project future air temperatures and precipitation on a 25 km grid for the Ganges basin in northern India, with a view to assessing impact of climate change on water resources and determining what multi-sector adaptation measures and policies might be adopted at different spatial scales. The RCM results suggest an increase in mean annual temperature, averaged over the Ganges basin, in the range 1-4 oC over the period from 2000 to 2050, using the SRES A1B forcing scenario. Projections of precipitation indicate that natural variability dominates the climate change signal and there is considerable uncertainty concerning change in regional annual mean precipitation by 2050. The RCMs do suggest an increase in annual mean precipitation in this region to 2050, but lack significant trend. Glaciers in headwater tributary basins of the Ganges appear to be continuing to decline but it is not clear whether meltwater runoff continues to increase. The predicted changes in precipitation and temperature will probably not lead to significant increase in water availability to 2050, but the timing of runoff from snowmelt will likely occur earlier in spring and summer. Water availability is subject to decadal variability, with much uncertainty in the contribution from climate change. Although global social-economic scenarios show trends to urbanization, locally these trends are less evident and in some districts rural population is increasing. Falling groundwater levels in the Ganges plain may prevent expansion of irrigated areas for food supply. Changes in socio-economic development in combination with projected changes in timing of runoff outside the monsoon period will make difficult choices for water managers. Because of the uncertainty in future water availability trends, decreasing vulnerability by augmenting resilience is the preferred way to adapt to climate change. Adaptive policies are required to increase society's capacity to adapt to both anticipated and unanticipated conditions. Integrated solutions are needed, consistent at various spatial scales, to assure robust and sustainable future use of resources. For water resources this is at the river basin scale. At present adaptation measures in India are planned at national and state level, not taking into account the physical boundaries of water systems. To increase resilience adaptation plans should be made locally specific. However, as it is expected that the partitioning of water over the different sectors and regions will be the biggest constraint, a consistent water use plan at catchment and river basin scale may be the best solution. A policy enabling such river basin planning is essential.