Impact of the North Sea–Caspian pattern on meteorological drought and vegetation response over diverging environmental systems in western Eurasia

Emerging drought stress on vegetation over western Eurasia is linked to varying teleconnection patterns. The North Sea–Caspian Pattern (NCP) is a relatively less studied Eurasian teleconnection pattern, which has a role on drought conditions and the consequence of changing conditions on vegetation. Between 1981 and 2015, we found that the Standardized Precipitation Index (SPI) and the Normalized Difference Vegetation Index (NDVI) have different trend patterns over various parts of western Eurasia. Specifically, the vegetation greenness is linked with wetter conditions over Scandinavia, and vegetation cover decreases over a drying central Asia. However, western Russia and Franceare paradoxically becoming greener under drier conditions. Using the Budyko framework, such paradoxical patterns are found in energy-limited environmental systems, where vegetation growth is primarily promoted by warmer temperatures. While most studies focused on the impacts of the North Atlantic Oscillation (NAO), we test whether the NCP explains better the variability of meteorological drought and vegetation response over western Eurasia. We hypothesised that the positive phases of the NCP are correlated to high pressure anomalies over the North Sea, which can be associated with weakening onshore moisture advection, leading to warmer and dryness conditions. These conditions are driving vegetation greening, as western Eurasia is mainly energy limited. However, we show that as the climate is warming along with the teleconnection impacts, the future ecosystem over western Eurasia will be transferred from energy-limited to water-limited systems. This suggests that the observed vegetation greening over past three decades is unlikely to sustain in the future

Atmospheric Exchanges of Riparian Vegetation in a Semi-Arid Environment

The relationship between photosynthesis and transpiration from riparian vegetation in a semi-arid region is the primary focus of interest in this study. An eddy covariance system was used to measure fluxes of energy, momentum, and carbon over an extended period which included a monsoon season and a subsequent prolonged dry period. The photosynthetic portion of the measured CO2 flux was obtained by subtracting the mean value of nighttime CO2 flux (respiration) from the daytime CO2 flux, and the resulting photosynthesis estimates were then compared with transpiration and other variables. Because the data revealed a somewhat complex relationship between photosynthesis and transpiration on both an hourly and a daily basis, a further analysis was made involving both the calculation of the canopy conductance and a 'stand alone' version of the Simple Biosphere (SiB2) Model. The results showed the assumed relationship between canopy photosynthesis and canopy conductance used in SiB2 is inconsistent with observations, however Monteith's suggestion that the ratio of the CO2 concentration inside leaves to that outside leaves is approximately constant, which leads to a linear relationship between canopy conductance and photosynthesis, is consistent with observations.Digitized from paper copies provided by the Department of Hydrology & Atmospheric Sciences

Improving the parameterization of land-surface interactions in GCMs using field data

General Circulation Models are important tools in the study of the earth's climate system. The terrestrial surface forms the lower boundary to such models over continents and a well-defined lower boundary is crucial for reliable climate simulations because the Earth interacts with the atmosphere via this boundary. The primary motivation for this research is to improve the parameterization of these interactions in General Circulation Models using field data and calibration techniques. For this purpose, a recent version of Biosphere-Atmosphere Transfer Scheme was selected, studied, and then calibrated for five different vegetation types using multi-criteria calibration techniques. The associated parameter sets were then tested in a ten-year climate integration with Version 3 of the Community Climate Model. The present study explored the methodology needed to use the growing number of relevant field data sets effectively and efficiently better to parameterize the land surface in a GCM. It showed that such field data can, indeed, be used in this way, not only to improve simulations but also to understand models' capabilities and deficiencies. Calibrating the land surface parameterization significantly improved simulations relative to the original default parameterization but several physically based land surface models studied, once calibrated, were found to give equally good simulations of the land surface processes. The primary results are that it is possible to obtain a single preferred parameter sets for different vegetation types using multi-criteria calibration, and that using calibrated parameter sets in climate models can improve the representation of surface exchanges and the modeled climate given by a GCM

Projected river discharge in the Euphrates−Tigris Basin from a hydrological discharge model forced with RCM and GCM outputs

Artículo de publicación ISIThe hydrological discharge (HD) model of Max Planck Institute for Meteorology is forced by a variety of climate model datasets to investigate the future of discharge in the Euphrates−Tigris Basin. The data include daily time series of surface runoff and sub-surface runoff outputs of 2 global climate models (GCMs) (the SRES A1B scenario simulation of ECHAM5/MPIOM and the RCP 4.5 scenario simulation of MPI-ESM-LR) and the dynamically downscaled outputs of ECHAM5/MPIOM and NCAR-CCSM3 scenario (SRES A1FI, A2 and B1) simulations. The suite of simulations enables a comprehensive analysis of the projected river discharge, and allows a comparison between CMIP5 simulations of MPI-ESM-LR and CMIP3 results from its predecessor ECHAM5/MPIOM on a basin scale. We demonstrate that HD simulations forced with relatively low-resolution GCM outputs are not good at reproducing the seasonal cycle of discharge, which is typically characterized by less flow in the peak season and an earlier peak in annual discharge. Simulations forced with the MPI-ESM-LR yield more robust information on the annual cycle and timing of the annual peak discharge than ECHAM5-forced simulations. In contrast to GCM-forced simulations, high-resolution RCM-forced simulations reproduce the annual cycle of discharge reasonably well; however, overestimation of discharge during the cold season and bias in the timing of springtime snowmelt peaks persist in the RCM-forced simulations. Different RCM-forced scenario simulations indicate substantial decreases in mean annual discharge for the Euphrates and Tigris Rivers by the end of the century, ranging from 19−58%. Significant temporal shifts to earlier days (3−5 wk by the end of the 21st century) in the center time of the discharges are also projected for these rivers. As the basin is considered water-stressed and the region is strongly influenced by water-scarcity events, these unfavorable changes may potentially increase water disputes among the basin countries

The merit of the North Sea - Caspian Pattern in explaining climate variability in the Euro-Mediterranean region

Teleconnection patterns are one of the key features of understanding high-frequency natural climate variability. The North Sea - Caspian Pattern (NCP) was identified as a middle tropospheric dipole and, its hydroclimatological implications were substantially restricted to the Eastern Mediterranean region. Thus, hydroclimatological influences of the NCP in the Euro-Mediterranean region were investigated in a comparative approach with dominant tropospheric teleconnections in the Eurasian region, and synoptic features such as ridge-trough positioning and strength. By using high-resolution ERA5 reanalysis data, cross-correlations between indexes, anticorrelations at 500 hPa, and composite anomaly maps for seasonally representative months were produced to understand the working mechanism of NCP. Comparisons included East Atlantic / Western Russian (EAWR), a rotated principal component analysis (RPCA) variant of NCP which utilizes pole-based representation Analysis revealed that NCP was correlated well with the Mediterranean trough displacement, and the strength of the East Asian trough. Climate anomalies indicated by NCP were greater and more spatially consistent compared to other teleconnections. NCP also had higher contrast of temperature and precipitation than EAWR based on the composite anomaly maps. In conclusion, NCP explained climate variability in all seasons linking remote centers of action within Eurasia's east and west extremes

Climate change impacts in the Euphrates-Tigris Basin based on different model and scenario simulations

Hydro-climatic effects of future climate change in the Euphrates-Tigris Basin are investigated using dynamically downscaled outputs of different GCM (ECHAM5, CCSM3 and HadCM3) - emissions scenario (A1FI, A2 and B1) simulations. The suite of simulations (total five) enables an analysis taking into account the A2 emission scenario simulations of three different GCMs and another analysis based on the three different emissions scenario (A1FI, A2 and B1) simulations of one GCM (CCSM3). All scenario simulations indicate winter surface temperature increases in the entire basin, however, the increase is larger in the highlands. The greatest increase in the annual temperature by the end of century belongs to the CCSM3 A1FI simulation with an increment of 6.1 degrees C in the highlands. There is a broad agreement amongst the simulations in terms of the winter precipitation decrease in the highlands and northern parts and increase in the southern parts of the basin. A remarkable impact of warming could be seen on the snow water equivalent in the highlands where each simulation points out statistically significant decreases ranging from 55% (lower emissions) to 87% (higher emissions). Statistically significant declines (25-55%) are found for the annual surface runoff of the main headwaters area. Moreover, significant temporal shifts to earlier days (between 18 and 39 days depending on the scenario) are projected to occur in the surface runoff timing in the headwaters region. Projected annual surface runoff changes in all simulations suggest that the territories of Turkey and Syria within the basin are most vulnerable to climate change as they will experience significant decreases in the annual surface runoff. Eventually, however, the downstream countries, especially Iraq, may suffer more as they rely primarily on the water released by the upstream countries. The substantial changes in the hydro-climate of the basin, therefore, are likely to increase the challenges associated with the management of several dam reservoirs and hydropower plants in the basin in addition to causing further impacts on physical and biological components of the ecosystems along these rivers

Impact of the North Sea–Caspian pattern on meteorological drought and vegetation response over diverging environmental systems in western Eurasia

International audienceEmerging drought stress on vegetation over western Eurasia is linked to varying teleconnection patterns. The North Sea-Caspian Pattern (NCP) is a relatively less studied Eurasian teleconnection pattern, which has a role on drought conditions and the consequence of changing conditions on vegetation. Between 1981 and 2015, we found that the Standardized Precipitation Index (SPI) and the Normalized Difference Vegetation Index (NDVI) have different trend patterns over various parts of western Eurasia. Specifically, the vegetation greenness is linked with wetter conditions over Scandinavia, and vegetation cover decreases over a drying central Asia. However, western Russia and Franceare paradoxically becoming greener under drier conditions