Das Projekt "Scientific Support for Regional Downscaling of Precipitation and Temperature Data for Climate Change Impact Assessment in the Nile Equatorial Lakes Region" wird vom Umweltbundesamt gefördert und von Universität Stuttgart, Institut für Wasserbau durchgeführt. The goal of this study was to enable a prognosis on the future rainfall conditions of the Nile Equatorial Lakes regions by delivering time-series of monthly rainfall sums for the time-period from 2021 to 2050 that can be used for all kinds of applications. One example might be the dimensioning of hydraulic structures. In these very long lasting investments, future climatic conditions have to be considered during present planning and construction.The principal sources of information on future climate conditions are General Circulation Models (GCMs). These are physically based atmospheric models that resemble a numerical weather prediction system but on a much coarser scale. This forecast cannot be perfect. Especially, it cannot predict single values, e. g. if January 2050 will be rather wet or dry, but only climatic references, i.e. state, if Januaries in general will become wetter or dryer in the future. Even if the predictions of a GCM were perfect, its output could not be used directly for hydrological purposes, due to its coarse resolution. The monthly precipitation values that are provided by the GCM present the spatially averaged precipitation over a grid cell of several thousand square kilometres. This 'block rainfall' can differ significantly from rainfall measured at the ground. Rain gauges are influenced by local effects like micro climatic conditions or orographic effects of mountain ranges that GCMs are not able to resolve.This study combined the information from different data sources. As global trend information, monthly precipitation values from two GCMs (ECHAM5 and HadCM3) were used. Three CO2-emission scenarios (A1b, A2 and B1) were considered in this data. As local ground reference observed monthly rainfall sums from several rain gauges in East Africa as well as from three reanalysis projects (Climate Research Unit, University of Delaware and GPCC) were used.At each rain gauge or observation point in the reanalysis a technique called 'Quantile-Quantile-Transformation' was applied to establish a relationship between the Cumulative Distribution Function (CDF) of the GCMs and that of the ground references during the calibration period from 1961-1990. The CDFs were fitted by non-parametric Kernel-Smoothing. To account for potential shifts in the annual cycles of GCMs and ground references, the transformations was done separately for each month.Assuming that the relation between Global Model and local response will be constant in the future, the global predictions of the GCM can be downscaled to local scale, leading to future rainfall scenarios that are coherent with observed past rainfall.Combining the data from three CO2-emission scenarios of two GCM with three reanalysis data sets, an ensemble of 18 different rainfall time-series was created for each observation point. The range of this ensemble helps to estimate the possible uncertainties in the prognosis of future monthly precipitation sums from 2021 to 2050.
Das Projekt "Fire, climate change and human impact in tropical ecosystems: long-term biodiversity and stand dynamics of tropical vegetation" wird vom Umweltbundesamt gefördert und von Universität Bern, Departement Biologie, Institut für Pflanzenwissenschaften durchgeführt. Forecasted change in precipitation may lead to an increase of biomass in area covered by savannah and to a consequent increase in biomass burning, affecting the carbon emissions at global scale. Understanding how tropical ecosystems will react to those changes is relevant particularly for East Africa, where population density is the highest of the continent. We generated high-resolution sediment charcoal data spanning the last 2000 years across a climatic gradient (wet to dry savannah) to assess the long-term impact of fire, climate and land use on tropical savannah ecosystems. Records of biomass burnings show contrasting fire pattern among the two regions. In wet savannah ecosystems, fire was limited by wetter periods until the colonial period (AD 1800), when biomass removal led to a decrease in burning. In contrast, in the dry setting of Kenya, fire conditions during the last 2k years peaked at intermediate rainfall, and increased in recent times following land use intensification. On the basis of our data we hypothesize that under a future scenario with increased rainfall fire will increase in the wet savannah and decrease in the (eastern) dry savannah, unless fuel will be limited by agriculture practices. Yet, it is not understood how important vegetation properties and ecosystem services such as plant biomass and diversity will respond to inter-annual to seasonal variation in the moisture balance, and how tropical species will cope with extreme events, such as droughts. The following proposal addresses highly relevant questions for todays key issues of biodiversity and the adaptation of vulnerable communities to global change. Additionally, it will contribute to ongoing multi-proxy research concerning the magnitude, frequency, and rates of past climate change in equatorial East Africa. Finally, the project will improve our understanding of tropical ecosystem functioning and its interaction with cultural and economic systems at local to regional scales.
Das Projekt "Fire, climate change and human impact in tropical ecosystems: paleoecological insights from the East African region" wird vom Umweltbundesamt gefördert und von Universität Bern, Departement Biologie, Institut für Pflanzenwissenschaften durchgeführt. Fire is an important ecological factor of disturbance in African tropical ecosystems, driving vegetation dynamics and regulating nutrient cycling and biomass. The significance of wildfires for future environmental processes is underlined by recent projections of global warming, which predict more frequent and more intense extremes of natural events. Particularly in East Africa, where population growth and natural resource exploitation are among the highest in the world, strategies for sustainable economic development will have to deal with environmental changes at regional to continental scales. Understanding such complex responses to global change requires long-term records, since only they provide a way to observe the response of ecosystems to large-magnitude environmental change on decadal and longer time scales. We use high-resolution charcoal data from lake-sediment cores to reconstruct past fire/climate/human interactions in East Africa, aiming in particular 1) to understand how the fire regime influenced vegetation dynamics during the last millennia in savannah-type and sub-humid tropical ecosystems, 2) to test whether changes in fire regime are coupled with episodes of past climatic extremes inferred from the available sedimentological data, and 3) to detect early human deforestation and the timing of increased fire frequencies beyond its natural variability. Additionally, we will apply novel techniques such as molecular markers (benzene polycarboxylic acids, BPCAs) to complement the standard sedimentary approaches to reconstruct Holocene fire history. The proposed research addresses new, highly relevant questions for today's key issue of sustainability (economic development, natural resource management, adaptation of vulnerable communities to global change). Additionally, it will contribute with new high-quality data to ongoing multi-proxy research concerning the magnitude, frequency, and rates of past climate change in equatorial East Africa. Finally, the project will contribute to our understanding of tropical ecosystem functioning and its interaction with regional, cultural, and economic systems.