Drought assessment in a changing climate with the joint deficit index

2020 ◽  
Author(s):  
Hans Van de Vyver ◽  
Joris Van den Bergh ◽  
Bert Van Schaeybroeck
Keyword(s):  
Climate Model ◽  
Regional Climate ◽  
Gaussian Copula ◽  
Drought Assessment ◽  
Covariance Models ◽  
Climate Model Simulations ◽  
Joint Deficit Index ◽  
The Impact

<p>The characterization of droughts is very dependent on the time scale that is involved. To obtain an overall drought assessment, the cumulative effects of water deficits over different times need to be examined together. For instance, the joint deficit index (JDI) is based on multivariate probabilities of precipitation over various time scales from 1- to 12-months, and was constructed from empirical copulas. We examine the Gaussian copula model for the JDI, and we model the covariance across the temporal scales with a two-parameter function that is commonly used in the specific context of spatial statistics or geostatistics. The validity of the covariance models is demonstrated with long-term precipitation series.</p><p>Next, we assess the impact of climate change on future droughts, based on the JDI. We select an ensemble of CORDEX regional climate model simulations, under the emission pathways RCP4.5 and RCP8.5. The CORDEX resolution used is 0.11 degree (EUR-11). In particular, distributional changes in the JDI are analysed for the Brussels-Capital Region. This area contains climatological and synoptic stations that are operated by the Royal Meteorological Institute of Belgium, with long-term series.</p><p> </p>

scholarly journals Assessing the impact of SSTs on a simulated medicane using ensemble simulations

2018 ◽  
Author(s):  
Robin Noyelle ◽  
Uwe Ulbrich ◽  
Nico Becker ◽  
Edmund P. Meredith
Keyword(s):  
Climate Model ◽  
Regional Climate ◽  
Western Mediterranean ◽  
Tyrrhenian Sea ◽  
Western Mediterranean Basin ◽  
Minor Influence ◽  
Climate Model Simulations ◽  
Upper Level ◽  
A Minor ◽  
The Impact

Abstract. The sensitivity of the October 1996 medicane in the western Mediterranean basin to sea surface temperatures (SSTs) is investigated via 24-member ensembles of regional climate model simulations. Eleven ensembles are created by uniformly changing SSTs in a range of −4 K to +6 K from the observed field, with a 1 K step. By using a modified phase space diagram and a simple compositing method, it is shown that the SST state has a minor influence on the tracks of the cyclones, but a strong influence on their intensities. Increased SSTs lead to greater probabilities of tropical transitions, to stronger low- and upper-level warm cores, and to lower pressure minima. The tropical transition occurs sooner and lasts longer, which enables a greater number of transitioning cyclones to survive landfall over Sardinia and to re-intensify in the Tyrrhenian Sea. The results demonstrate that SSTs influence the intensity of fluxes from the sea, which leads to greater convective activity before the storms reach their maturity. These results suggest that the processes at steady-state for medicanes are very similar to tropical cyclones.

scholarly journals The climate in the Baltic Sea region during the last millennium simulated with a regional climate model

2012 ◽  
Vol 8 (5) ◽  
pp. 1419-1433 ◽  
Author(s):  
S. Schimanke ◽  
H. E. M. Meier ◽  
E. Kjellström ◽  
G. Strandberg ◽  
R. Hordoir
Keyword(s):  
Baltic Sea ◽  
Climate Model ◽  
Regional Climate ◽  
Last Millennium ◽  
Nutrient Loads ◽  
The Baltic Sea ◽  
Baltic Sea Region ◽  
The Baltic ◽  
The Impact

Abstract. Variability and long-term climate change in the Baltic Sea region is investigated for the pre-industrial period of the last millennium. For the first time dynamical downscaling covering the complete millennium is conducted with a regional climate model in this area. As a result of changing external forcing conditions, the model simulation shows warm conditions in the first centuries followed by a gradual cooling until ca. 1700 before temperature increases in the last centuries. This long-term evolution, with a Medieval Climate Anomaly (MCA) and a Little Ice Age (LIA), is in broad agreement with proxy-based reconstructions. However, the timing of warm and cold events is not captured at all times. We show that the regional response to the global climate anomalies is to a strong degree modified by the large-scale circulation in the model. In particular, we find that a positive phase of the North Atlantic Oscillation (NAO) simulated during MCA contributes to enhancing winter temperatures and precipitation in the region while a negative NAO index in the LIA reduces them. In a second step, the regional ocean model (RCO-SCOBI) is used to investigate the impact of atmospheric changes onto the Baltic Sea for two 100 yr time slices representing the MCA and the LIA. Besides the warming of the Baltic Sea, the water becomes fresher at all levels during the MCA. This is induced by increased runoff and stronger westerly winds. Moreover, the oxygen concentrations in the deep layers are slightly reduced during the MCA. Additional sensitivity studies are conducted to investigate the impact of even higher temperatures and increased nutrient loads. The presented experiments suggest that changing nutrient loads may be more important determining oxygen depletion than changes in temperature or dynamic feedbacks.

scholarly journals Where Does the Irrigation Water Go? An Estimate of the Contribution of Irrigation to Precipitation Using MERRA

2013 ◽  
Vol 14 (1) ◽  
pp. 275-289 ◽  
Author(s):  
Jiangfeng Wei ◽  
Paul A. Dirmeyer ◽  
Dominik Wisser ◽  
Michael G. Bosilovich ◽  
David M. Mocko
Keyword(s):  
Hydrological Model ◽  
Climate Model ◽  
Regional Climate ◽  
Back Trajectory ◽  
Percentage Increase ◽  
Weather Forecasts ◽  
Explicit Consideration ◽  
Precipitation Increase ◽  
Climate Model Simulations ◽  
The Impact

Abstract Irrigation is an important human activity that may impact local and regional climate, but current climate model simulations and data assimilation systems generally do not explicitly include it. The European Centre for Medium-Range Weather Forecasts (ECMWF) Interim Re-Analysis (ERA-Interim) shows more irrigation signal in surface evapotranspiration (ET) than the Modern-Era Retrospective Analysis for Research and Applications (MERRA) because ERA-Interim adjusts soil moisture according to the observed surface temperature and humidity while MERRA has no explicit consideration of irrigation at the surface. But, when compared with the results from a hydrological model with detailed considerations of agriculture, the ET from both reanalyses show large deficiencies in capturing the impact of irrigation. Here, a back-trajectory method is used to estimate the contribution of irrigation to precipitation over local and surrounding regions, using MERRA with observation-based corrections and added irrigation-caused ET increase from the hydrological model. Results show substantial contributions of irrigation to precipitation over heavily irrigated regions in Asia, but the precipitation increase is much less than the ET increase over most areas, indicating that irrigation could lead to water deficits over these regions. For the same increase in ET, precipitation increases are larger over wetter areas where convection is more easily triggered, but the percentage increase in precipitation is similar for different areas. There are substantial regional differences in the patterns of irrigation impact, but, for all the studied regions, the highest percentage contribution to precipitation is over local land.

scholarly journals Explicit Convection and Scale-Aware Cumulus Parameterizations: High-Resolution Simulations over Areas of Different Topography in Germany

2018 ◽  
Vol 146 (6) ◽  
pp. 1925-1944 ◽  
Author(s):  
Andreas Wagner ◽  
Dominikus Heinzeller ◽  
Sven Wagner ◽  
Thomas Rummler ◽  
Harald Kunstmann
Keyword(s):  
High Resolution ◽  
Land Surface ◽  
Climate Model ◽  
Regional Climate ◽  
Surface Characteristics ◽  
Radar Data ◽  
Explicit Calculation ◽  
Climate Model Simulations ◽  
Convection Parameterization ◽  
The Impact

An increase in the spatial resolution of regional climate model simulations improves the representation of land surface characteristics and may allow the explicit calculation of important physical processes such as convection. The present study investigates further potential benefits with respect to precipitation, based on a small ensemble of high-resolution simulations with WRF with grid spacings up to 1 km. The skill of each experiment is evaluated regarding the temporal and spatial performance of the simulation of precipitation of one year over both a mountainous region in southwestern Germany and a mainly flat region in northern Germany. This study allows us to differentiate between the impact of grid spacing, topography, and convection parameterization. Furthermore, the performance of a state-of-the-art convection parameterization scheme in the gray zone of convection is evaluated against an explicit calculation of convection only. Our evaluation demonstrates the following: high-resolution simulations (5 and 1 km) are generally able to represent the diurnal cycle, structure, and intensity distribution of precipitation, when compared to observational datasets such as radar data and interpolated station data. The influence of the improved representation of the topography at higher resolution (1 km) becomes apparent in complex terrain, where the localization of precipitation maxima is more accurate, although these maxima are overestimated. In flat areas, differences in spatial evaluations arise between simulations with parameterized and explicitly calculated convection, whereas smaller grid spacings (1 km vs 5 km) show hardly any impact on precipitation results.

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