Browsing by Subject "Aufforstung"

Now showing 1 - 3 of 3

Mitigate habitat degradation in the semiarid Brazil : potential and limitation of the endemic tree Spondias tuberosa Arruda
(2017) Mertens, Jan Heiko; Sauerborn, Joachim
Semiarid regions cover 15 % of the global land mass and are inhabited by approximately one billion people. Due to the strong rural character of these regions the well-being of 13 % of the world’s population relying directly or indirectly on their ecosystem services. One of the most densely populated semiarid region is the Caatinga biome, that is located in the Brazilian Northeast. Its climate is hot semiarid (BSh) with little, erratic, and seasonal precipitation, ranging from 250 to 900 mm per year. The average annual temperatures range from 23°C to 27°C. An evapotranspiration above 2000 mm per year results in a negative water balance during 7 to 11 months. The deciduous natural Caatinga vegetation ranges from tropical dry forest to open shrubby vegetation, with a seasonal herbaceous layer. Loss of its natural vegetation due to wood extraction, pasturing, and inappropriate land-use led to habitat degradation in up to 80 % of the area of the Caatinga biome. A degraded habitat jeopardizes the ecosystem services of the biome and poses a direct threat to its dwellers. In order to mitigate further habitat degradation an alternative land-use strategy is necessary to substitute or cut back prevailing land-use. The agro-industrial utilization of the fructiferous multipurpose tree Spondias tuberosa Arruda (Anacardiaceae), endemic to the Caatinga, has the potential to be a viable alternative to current irrigation farming and extensive animal husbandry. The current utilization of S. tuberosa is limited to extractivism of its fruits that lacks sustainability and appears to be a finite resource. The natural population of S. tuberosa presents a weakening natural regeneration with a resultant over aged S. tuberosa population. Poor natural regeneration results from a multifactorial problem. At this juncture, S. tuberosa is not considered endangered based on the criteria of the International Union for Conservation of Nature, due to lacking information for a Red List of Threatened Species threat assessment. However, the combination of expected changing environmental conditions within the Caatinga and restricted natural regeneration of S. tuberosa, both discussed in literature, provides a strong evidence, that the S. tuberosa faces a high risk to become extinct. This work aims to provide a first basis for a scientifically-backed, extensive cropping system for S. tuberosa on disturbed Caatinga sites meliorated by the use of biochar, clay substrate, and goat manure. The effect of biochar, clay substrate, and goat manure with or without additional mineral fertilization as soil conditioner in planting holes were tested in a 23-months field experiment in a marginal Arenosol. Further, it was studied, whether changed soil physical conditions support establishment and development of one-year-old S. tuberosa seedlings. At given application rates neither biochar nor clay substrate significantly affected soil physical parameters of the experimental soil. The application rate of 10 % v/v clay substrate, chosen from literature, seems to be too little to be affective on the experimental Arenosol, that was poor in fine particles (< 0.02 mm). The utilized biochar were proven hydrophobic and presumingly little porous duo to a low pyrolysis temperature. Both combined could explain the absence of a significant biochar‑mediated change of soil physical parameters. Goat manure significantly increased total porosity, and significantly reduced soil bulk density. The water content at permanent wilting point, and volumetric water content within the planting holes during the experiment were significantly increased owing to melioration with goat manure. Due to a strong correlation (R2 = 0.75) of water content at field capacity and water content at permanent wilting point, the available water capacity, an important target parameter for plant production, remained unchanged. Neither stem growth nor seedling survival was significantly affected by initial nutrient supplies or melioration. Conversely, fine root growth and root tuber growth were significantly affected by melioration. Goat manure in the planting holes led to significantly reduced fine root dry matter. Since fine root dry matter showed a weak but significant negative correlation with soil water content, the fine root reduction was evidently caused by increased soil water content resulting from goat manure application. The goat manure application also affected tuber growth significantly, and led to larger tubers. In contrast to the fine roots, root tuber growth did not respond to soil water content but showed a significant correlation with soil bulk density and total porosity. Reduced soil bulk density and increased soil porosity after goat manure addition application led to higher tuber volume.
Sensitivity of land-atmosphere coupling strength in dependence of land cover and atmospheric thermodynamics over Europe
(2023) Jach, Lisa; Wulfmeyer, Volker
Biogeophysical feedbacks between the land surface and the atmosphere have been identified to heavily control the climate system. Land-atmosphere (L-A) coupling strength is a concept to quantify the feedback processes. However, the quantification is still subject to uncertainties, in particular, in the context of land surface influences on local convective precipitation. On the one hand, feedback processes are the result of a chain of complex interactions between various components in the L-A system all exhibiting spatiotemporal variability. On the other hand, L-A coupling strength is not a directly measurable quantity. It can be assessed with different scientific approaches, which makes the quantification dependent on the methodology and the availability of suitable data sets. The aim of this doctoral thesis is to investigate the impact of changes in the vegetation cover and the atmospheric thermodynamic conditions on the long-term coupling signal between the land surface and the triggering of deep moist convection during the European summer. The ‘convective triggering potential – low-level humidity index’ framework, which is a commonly used L-A coupling metric, classifies a day in favor for L-A coupling or not, based on the prevailing thermodynamic conditions in the atmosphere. The daily classifications are used to measure the frequency of days with favorable conditions during the study period, and to identify regions with high frequencies of favorable conditions as coupling hot spots. The framework is applied to model output from regional climate model (RCM) simulations with WRF-NoahMP with diverging land cover conducted over the historical period 1986-2015 for the Euro-CORDEX domain. Impacts of changes in vegetation cover are analyzed by comparing the L-A coupling strength from two sensitivity experiments with idealized extreme land use and land cover changes (LULCCs) against a simulation with realistic land cover. A posteriori modifications to the temperature and moisture output fields of the simulation with realistic land cover were implemented to analyze impacts of systematic changes in the atmospheric thermodynamic conditions. A potential coupling hot spot with predominantly positive feedbacks was identified over Eastern Europe. In Southern Europe and Europe’s coastal areas, the coupling is regularly inhibited by very dry, very wet or stable conditions in the atmosphere. The location of the hot spot appeared insensitive to LULCCs and changes in the thermodynamic conditions. None of the sensitivity tests within a realistic range of temperature and moisture modifications for a recent climate period, led to a disappearance of the hot spot or to overcome the causes for inhibiting coupling in the respective areas in summer. Nevertheless, the experiments demonstrated also considerable variance of the coupling strength within the hot spot region. LULCCs changed the turbulent heat fluxes from the land surface, and thus the atmospheric boundary layer (ABL) heating and moistening. This impacted the boundary layer development of each day. It also caused changes in the average thermodynamic characteristics during the study period, which changed the frequency of favorable pre-conditioning for convection triggering and enhanced the variance in the coupling strength in the hot spot. Both effects were identified to influence the land surface control on the occurrence of convective precipitation. Furthermore, the sensitivity tests with a posteriori modifications revealed uncertainties in the predominant atmospheric response to differently wet surfaces around the Black Sea, shown by a disagreement in the predominant coupling pathway between the modification cases. The findings further indicate uncertainty in whether the hot spot expands over Central Europe, as the feedback signal was sensitive to changes in temperature and moisture. Additionally, the model has a warm and dry bias in this area, which suggests an overestimation of the humidity deficit. The large humidity deficit, in turn, was the inhibiting factor for a high frequency of occurrence of favorable pre-conditions for deep moist convection. The analyses reveal a sensitivity of the L-A coupling strength and atmospheric response to the prevailing land surface and atmospheric conditions in the hot spot. This highlights the need to consider both the land surface state and its impact on L-A coupling strength with respect to predictions of convective precipitation events in strongly coupled regions (and periods). Given that L-A coupling provides predictive skill for climate projections and seasonal forecasts, improved understanding about causes of variability in L-A coupling strength is crucial for improvements therein.
The impact of irrigated biomass plantations on mesoscale climate in coastal arid regions
(2015) Branch, Oliver; Wulfmeyer, Volker
Large-scale agroforestry in coastal arid and semi-arid regions could provide a geoengineering solution to anthropogenic climate change. Since agroforestry may impact on mesoscale climate in unknown ways, urgent research into potential impacts of large-plantations is needed to fully assess the viability and optimal placement for such schemes. Validated mesoscale simulations provide insights into feedbacks between land surface and atmosphere, particularly with respect to convective processes. Simulations of irrigated Simmondsia chinensis (jojoba) plantations were carried out with the WRF-NOAH atmosphere-land surface model using prescribed land surface and plant parameters. A sub-surface irrigation algorithm was developed based on critical soil moisture stress levels and implemented into the model code. The simulation of desert and plantation land surfaces was validated with field data from two sites in the Negev Desert - an arid desert site and a 400 ha jojoba plantation. For desert and vegetated surfaces, the model output of diurnal meteorological quantities and energy fluxes generally match well with the respective observations. Diurnal 2m-temperatures over the desert and plantation are matched by the model to within ± 0.2 °C and ± 1.5 °C, respectively. Wind speeds for both surfaces match to within 0.5 ms−1 and plantation latent heat is reproduced to within ± 20 Wm−2. Subsequent to validation, larger plantations of 100 km × 100 km were then simulated in two coastal arid regions, Israel and Oman over a period of one month and compared with control runs, without plantations. In Oman, convection and precipitation were triggered or enhanced by the plantation over multiple days whereas in Israel almost no impacts were observed. Two mechanisms were responsible for observed convection initiation: turbulent vertical transport of scalars due to increased surface heating and roughness as well as a low pressure-induced convergence at the canopy leeside. The main contributors to the surface heating effect were reduced albedo and the high water-use efficiency exhibited by specialist desert species. The combination of increased net surface radiation and high stomatal resistances significantly limited transpiration and led to a surplus in sensible heat flux compared with the surrounding soils (> 100 Wm−2). In Oman, convection initiation triggered by the plantation tended to occur on days when a high mid-tropospheric temperature lapse rate and significant surface air humidity were present. Israel exhibits more stable lapse rates during summer and drier conditions aloft, both of which suppressed convection significantly, even with a similar land surface perturbation. The initiation of moist convection at the mesoscale is therefore strongly controlled by prevailing synoptic conditions. A regional climatological analysis of temperature and humidity ECMWF reanalysis data and station precipitation data indicate that the south-west of North America has particularly suitable conditions for impacts. Coastal locations in Baja California and the Sonoran Desert exhibit a seasonal concurrence of monsoonal instability, high surface humidity and integrated column water vapor, but at the same time low precipitation. Therefore plantation impacts on convection there are likely and could be beneficial in terms of higher amounts of precipitation. These findings indicate that mesoscale convective events can be triggered by large plantations within arid and semi-arid regions and that these effects may be controllable via judicious placement of such schemes. Thus arid agroforestry has the potential not only to increase precipitation and reverse desertification within arid and semi-arid regions, but also to mitigate climate change if implemented on very large scales.