309 research outputs found
CESM simulation output; postprocessed and used for Thiery et al., 2019
No full textThese CESM output files represent the basis for producing the figures shown in Thiery, W., Visser, A.J., Fischer, E.M., Hauser, M., Hirsch, A.L., Lawrence, D.M., Lejeune, Q., Davin, E.L., Seneviratne, S.I., Warming of hot extremes alleviated by expanding irrigation. In particular, the files serve as input for the analysis and plotting scripts available on the through the github repository of the Department of Hydrology and Hydraulic Engineering at VUB (https://github.com/VUB-HYDR/2019_Thiery_etal_NatComm). Together, data files and scripts allow to reproduce all figures except fig. 1, S2 and S3 of the aforementioned publication. The files are postprocessed CESM output. Scripts used to run CESM are available in the subdirectory run_cesm of the github repository, whereas scripts used to postprocess the raw CESM output are available in the subdirectory cesm_postprocessing.<br
A novel method for assessing climate change impacts in ecotron experiments
No full textAbstract: Ecotron facilities allow accurate control of many environmental variables coupled with extensive monitoring of ecosystem processes. They therefore require multivariate perturbation of climate variables, close to what is observed in the field and projections for the future. Here, we present a new method for creating realistic climate forcing for manipulation experiments and apply it to the UHasselt Ecotron experiment. The new methodology uses data derived from the best available regional climate model projection and consists of generating climate forcing along a gradient representative of increasingly high global mean air temperature anomalies. We first identified the best-performing regional climate model simulation for the ecotron site from the Coordinated Regional Downscaling Experiment in the European domain (EURO-CORDEX) ensemble based on two criteria: (i) highest skill compared to observations from a nearby weather station and (ii) representativeness of the multi-model mean in future projections. The time window is subsequently selected from the model projection for each ecotron unit based on the global mean air temperature of the driving global climate model. The ecotron units are forced with 3-hourly output from the projections of the 5-year period in which the global mean air temperature crosses the predefined values. With the new approach, Ecotron facilities become able to assess ecosystem responses on changing climatic conditions, while accounting for the co-variation between climatic variables and their projection in variability, well representing possible compound events. The presented methodology can also be applied to other manipulation experiments, aiming at investigating ecosystem responses to realistic future climate change
Modelling the water balance of Lake Victoria (East Africa) - Part 1: Observational analysis
No full text© 2018 Author(s). Lake Victoria is the largest lake in Africa and one of the two major sources of the Nile river. The water level of Lake Victoria is determined by its water balance, consisting of precipitation on the lake, evaporation from the lake, inflow from tributary rivers and lake outflow, controlled by two hydropower dams. Due to a scarcity of in situ observations, previous estimates of individual water balance terms are characterized by substantial uncertainties, which means that the water balance is often not closed independently. In this first part of a two-paper series, we present a water balance model for Lake Victoria, using state-of-the-art remote sensing observations, high-resolution reanalysis downscaling and outflow values recorded at the dam. The uncalibrated computation of the individual water balance terms yields lake level fluctuations that closely match the levels retrieved from satellite altimetry. Precipitation is the main cause of seasonal and interannual lake level fluctuations, and on average causes the lake level to rise from May to July and to fall from August to December. Finally, our results indicate that the 2004-2005 drop in lake level can be about half attributed to a drought in the Lake Victoria Basin and about half to an enhanced outflow, highlighting the sensitivity of the lake level to human operations at the outflow dam.sponsorship: We thank Daniel Kull for providing the daily outflow measurements of Lake Victoria and John Sutcliffe for his contributions. We also thank Willy Bauwens for sharing the HYDROMET lake level measurements and Seppe Deckers for the help with the classification of the hydrologic soil groups. Furthermore, we acknowledge the CLM community (clm-community.eu) for developing COSMO CLM2 and making the model code available. Computational resources and services used for the COSMO-CLM2 simulations were provided by the VSC (Flemish Supercomputer Center), funded by the Hercules Foundation and the Flemish Government department EWI. Wim Thiery was supported by an ETH Zurich postdoctoral fellowship (Fel-4515-1). The Uniscientia Foundation and the ETH Zurich Foundation are thanked for their support to this research. (Hercules Foundation, Flemish Government department EWI, ETH Zurich postdoctoral fellowship|Fel-4515-1, Uniscientia Foundation, ETH Zurich Foundation)status: Publishe
Drivers of future changes in East African precipitation
No full textPrecipitation amounts over East Africa have been declining over the last decades. These changes and future climate change over the region are highly debated. This study analyzes drivers of future precipitation changes over East Africa by applying a classification of circulation patterns on 15 historical and future members of the COordinated Regional climate Downscaling EXperiment. Typical circulation types (CTs) are obtained. Under a high emission scenario, changes in the frequency of occurrence of these CTsattribute for23%of the total change in precipitation over East Africa by the end of the century. The remaining part (77%) is not related to East African synoptics, e.g. changes in moisture content, local/mesoscale feedbacks, and changes in moisture influx. These other effects comprise increases in precipitation close to the equator and the Somali region, while decreases are found over northwestern Ethiopia, the Sudan region and the lake areas.sponsorship: We thank two anonymous referees for reviews that markedly improved our paper. This work was financially supported by the Belgian Science Policy Office (BELSPO) through the research project EAGLES. Wim Thiery is an ETH Zurich postdoctoral fellow, Matthias Demuzere is a postdoctoral fellow at the Research Foundation Flanders (FWO). The authors declare no conflict of interest. All data and methods to reproduce the results of this study are described in section 2 and the supporting information. The COST733class software is freely available and can be downloaded on the following web page http://cost733.geo.uni-augsburg.de/cost733class-1.2. CORDEX model data is freely available from the ESGF servers (http://esgf.llnl.gov/), ERA-Interim data from ECMWF (http://www.ecmwf.int/en/research/climate-reanalysis/era-interim) and PERSIANNCDR from NOAA (https://www.ncdc.noaa.gov/cdr/atmospheric/precipitation-persiann-cdr). (Belgian Science Policy Office (BELSPO))status: Publishe
Modelling the water balance of Lake Victoria (East Africa) - Part 2: Future projections
No full text© 2018 Author(s). Lake Victoria, the second largest freshwater lake in the world, is one of the major sources of the Nile river. The outlet to the Nile is controlled by two hydropower dams of which the allowed discharge is dictated by the Agreed Curve, an equation relating outflow to lake level. Some regional climate models project a decrease in precipitation and an increase in evaporation over Lake Victoria, with potential important implications for its water balance and resulting level. Yet, little is known about the potential consequences of climate change for the water balance of Lake Victoria. In this second part of a two-paper series, we feed a new water balance model for Lake Victoria presented in the first part with climate simulations available through the COordinated Regional Climate Downscaling Experiment (CORDEX) Africa framework. Our results reveal that most regional climate models are not capable of giving a realistic representation of the water balance of Lake Victoria and therefore require bias correction. For two emission scenarios (RCPs 4.5 and 8.5), the decrease in precipitation over the lake and an increase in evaporation are compensated by an increase in basin precipitation leading to more inflow. The future lake level projections show that the dam management scenario and not the emission scenario is the main controlling factor of the future water level evolution. Moreover, inter-model uncertainties are larger than emission scenario uncertainties. The comparison of four idealized future management scenarios pursuing certain policy objectives (electricity generation, navigation reliability and environmental conservation) uncovers that the only sustainable management scenario is mimicking natural lake level fluctuations by regulating outflow according to the Agreed Curve. The associated outflow encompasses, however, ranges from 14m 3 day -1 (-85 %) to 200m 3 day -1 (C100 %) within this ensemble, highlighting that future hydropower generation and downstream water availability may strongly change in the next decades even if dam management adheres to he Agreed Curve. Our results overall underline that managing the dam according to the Agreed Curve is a key prerequisite for sustainable future lake levels, but that under this management scenario, climate change might potentially induce profound changes in lake level and outflow volume.sponsorship: We acknowledge the CLM-community (https://www.clm-community.eu/, last access: 16 October 2018) for developing COSMO CLM2 and making the model code available. Computational resources and services used for the COSMO-CLM2 simulations were provided by the VSC (Flemish Supercomputer Centre), funded by the Hercules Foundation and the Flemish Government department EWI. In addition, we are grateful to the World Climate Research Programme (WRCP) for initiating and coordinating the CORDEX-Africa initiative and to the modelling centres for making their downscaling results publicly available through ESGF. Wim Thiery was supported by an ETH Zurich postdoctoral fellowship (Fel-45 15-1). The Uniscientia Foundation and the ETH Zurich Foundation are thanked for their support to this research. (Hercules Foundation, Flemish Government department EWI, ETH Zurich postdoctoral fellowship|Fel-45 15-1, Uniscientia Foundation, ETH Zurich Foundation)status: Publishe
Breeze effects at a large artificial lake: summer case study
No full textNatural lakes and big artificial reservoirs can affect the weather regime of surrounding areas but, usually,consideration of all aspects of this impact and their quantification is a difficult task. The Alqueva reservoir, the largest artificial lake in western Europe, located on the south-east of Portugal, was filled in 2004. It is a large natural laboratory that allows the study of changes in surface and in landscape and how they affect the weather in the region. This paper is focused on a 3-day case study, 22–24 July 2014, during which an intensive observation campaign was carried out. In order to quantify the breeze effects induced by the Alqueva reservoir, two simulations with the mesoscale atmospheric model Meso-NH coupled to the FLake freshwater lake model has been performed. The difference between the two simulations lies in the presence or absence of the reservoir on the model surface. Comparing the two simulation datasets, with and without the reservoir, net results of the lake impact were obtained. Magnitude of the impact on air temperature, relative humidity, and other atmospheric variables are shown. The clear effect of a lake breeze (5–7 m s −1 ) can be observed during daytime on distances up to 6 km away from the shores and up to 300 m above the surface. The lake breeze system starts to form at 09:00 UTC and dissipates at 18:00-19:00 UTC with the arrival of a larger-scale Atlantic breeze. The descending branch of the lake breeze circulation brings dry air from higher atmospheric layers (2–2.5 km) and redistributes it over the lake. It is also shown that despite its significant intensity the effect is limited to a couple of kilometres away from the lake borders
Climate change, hydrological variability, and declining cost of renewables reduce economic viability of African hydropower potential
No full textDeclining cost of renewables and climate change curb the need for African hydropower expansion
No full textAcross continental Africa, more than 300 new hydropower projects are under consideration to meet the future energy demand that is expected based on the growing population and increasing energy access. Yet large uncertainties associated with hydroclimatic and socioeconomic changes challenge hydropower planning. In this work, we show that only 40 to 68% of the candidate hydropower capacity in Africa is economically attractive. By analyzing the African energy systems' development from 2020 to 2050 for different scenarios of energy demand, land-use change, and climate impacts on water availability, we find that wind and solar outcompete hydropower by 2030. An additional 1.8 to 4% increase in annual continental investment ensures reliability against future hydroclimatic variability. However, cooperation between countries is needed to overcome the divergent spatial distribution of investment costs and potential energy deficits
Drought characteristics in Mediterranean under future climate change
No full textAbstract The present work aims to address the physical properties of different drought types under near-future climates in the Mediterranean. To do so, we use a multi-model mean of the bias-adjusted and downscaled product of five Earth System Models participating in the Coupled Model Intercomparison Project—phase6 (CMIP6), provided by Inter-Sectoral Impact Model Intercomparison Project (ISIMIP), under four shared socioeconomic pathways (SSP1–2.6, SSP2–4.5, SSP3–7.0, and SSP5–8.5) for the period 2021–2060, to estimate the Standardized Precipitation Evapotranspiration Index (SPEI) at 1-, 6-, and 12-month time scales, and address the meteorological, agricultural, and hydrological drought, respectively. Additionally, SPEI is calculated from the bias-adjusted CMIP6 historical simulations and the reanalysis ‘WFDE5’ for 1980–2014 as a historical and reference period. The comparison of the CMIP6 with WFDE5 reveals a consistently increasing tendency for drought occurrences in the Mediterranean, particularly for agricultural and hydrological drought time scales. Nonetheless, an overestimation in historical trend magnitude is shown by the CMIP6 with respect to WFDE5. The projection results depict drought frequencies ranging between 12 and 25% of the studied period 2021–2060, varying with regions and climate scenarios. The tendency to increase the drought frequency is more pronounced in the southern than northern Mediterranean countries. Drought severity is remarkable in the aggregated time scales; consequently, more pressure is foreseen in the food and water sectors. Drought seasonality reveals a higher tendency for drought occurrences in summer (autumn) months for the meteorological (agricultural) droughts. The driving factor(s) for drought occurrence strongly depends on regional climate characteristics
Neglected implications of land-use and land-cover changes on the climate-health nexus
No full textClimate change can substantially affect temperature-related mortality and morbidity, especially under high greenhouse gas emission pathways. Achieving the Paris Agreement goals require not only drastic reductions in fossil fuel-based emissions but also land-use and land-cover changes (LULCC), such as reforestation and afforestation. LULCC has been mainly analysed in the context of land-based mitigation and food security. However, growing scientific evidence shows that LULCC can also substantially alter climate through biogeophysical effects. Little is known about the consequential impacts on human health. LULCC-related impact research should broaden its scope by including the human health impacts. LULCC are relevant to several global agendas (i.e. Sustainable Development Goals). Thus, collaboration across research communities and stronger stakeholder engagement are required to address this knowledge gap
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