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- ItemAtmospheric dust modeling from meso to global scales with the online NMMB/BSC-Dust model – Part 2: Experimental campaigns in Northern Africa(München : European Geopyhsical Union, 2012) Haustein, K.; Pérez, C.; Baldasano, J.M.; Jorba, O.; Basart, S.; Miller, R.L.; Janjic, Z.; Black, T.; Nickovic, S.; Todd, M.C.; Washington, R.; Müller, D.; Tesche, M.; Weinzierl, B.; Esselborn, M.; Schladitz, A.The new NMMB/BSC-Dust model is intended to provide short to medium-range weather and dust forecasts from regional to global scales. It is an online model in which the dust aerosol dynamics and physics are solved at each model time step. The companion paper (Pérez et al., 2011) develops the dust model parameterizations and provides daily to annual evaluations of the model for its global and regional configurations. Modeled aerosol optical depth (AOD) was evaluated against AERONET Sun photometers over Northern Africa, Middle East and Europe with correlations around 0.6–0.7 on average without dust data assimilation. In this paper we analyze in detail the behavior of the model using data from the Saharan Mineral dUst experiment (SAMUM-1) in 2006 and the Bodélé Dust Experiment (BoDEx) in 2005. AOD from satellites and Sun photometers, vertically resolved extinction coefficients from lidars and particle size distributions at the ground and in the troposphere are used, complemented by wind profile data and surface meteorological measurements. All simulations were performed at the regional scale for the Northern African domain at the expected operational horizontal resolution of 25 km. Model results for SAMUM-1 generally show good agreement with satellite data over the most active Saharan dust sources. The model reproduces the AOD from Sun photometers close to sources and after long-range transport, and the dust size spectra at different height levels. At this resolution, the model is not able to reproduce a large haboob that occurred during the campaign. Some deficiencies are found concerning the vertical dust distribution related to the representation of the mixing height in the atmospheric part of the model. For the BoDEx episode, we found the diurnal temperature cycle to be strongly dependant on the soil moisture, which is underestimated in the NCEP analysis used for model initialization. The low level jet (LLJ) and the dust AOD over the Bodélé are well reproduced. The remaining negative AOD bias (due to underestimated surface wind speeds) can be substantially reduced by decreasing the threshold friction velocity in the model.
- ItemHow will organic carbon stocks in mineral soils evolve under future climate? Global projections using RothC for a range of climate change scenarios(München : European Geopyhsical Union, 2012) Gottschalk, P.; Smith, J.U.; Wattenbach, M.; Bellarby, J.; Stehfest, E.; Arnell, N.; Osborn, T.J.; Jones, C.; Smith, P.We use a soil carbon (C) model (RothC), driven by a range of climate models for a range of climate scenarios to examine the impacts of future climate on global soil organic carbon (SOC) stocks. The results suggest an overall global increase in SOC stocks by 2100 under all scenarios, but with a different extent of increase among the climate model and emissions scenarios. The impacts of projected land use changes are also simulated, but have relatively minor impacts at the global scale. Whether soils gain or lose SOC depends upon the balance between C inputs and decomposition. Changes in net primary production (NPP) change C inputs to the soil, whilst decomposition usually increases under warmer temperatures, but can also be slowed by decreased soil moisture. Underlying the global trend of increasing SOC under future climate is a complex pattern of regional SOC change. SOC losses are projected to occur in northern latitudes where higher SOC decomposition rates due to higher temperatures are not balanced by increased NPP, whereas in tropical regions, NPP increases override losses due to higher SOC decomposition. The spatial heterogeneity in the response of SOC to changing climate shows how delicately balanced the competing gain and loss processes are, with subtle changes in temperature, moisture, soil type and land use, interacting to determine whether SOC increases or decreases in the future. Our results suggest that we should stop looking for a single answer regarding whether SOC stocks will increase or decrease under future climate, since there is no single answer. Instead, we should focus on improving our prediction of the factors that determine the size and direction of change, and the land management practices that can be implemented to protect and enhance SOC stocks.
- ItemMonitoring hillslope moisture dynamics with surface ERT for enhancing spatial significance of hydrometric point measurements(Munich : EGU, 2015) Hübner, R.; Heller, K.; Günther, T.; Kleber, A.Besides floodplains, hillslopes are basic units that mainly control water movement and flow pathways within catchments of subdued mountain ranges. The structure of their shallow subsurface affects water balance, e.g. infiltration, retention, and runoff. Nevertheless, there is still a gap in the knowledge of the hydrological dynamics on hillslopes, notably due to the lack of generalization and transferability. This study presents a robust multi-method framework of electrical resistivity tomography (ERT) in addition to hydrometric point measurements, transferring hydrometric data into higher spatial scales to obtain additional patterns of distribution and dynamics of soil moisture on a hillslope. A geoelectrical monitoring in a small catchment in the eastern Ore Mountains was carried out at weekly intervals from May to December 2008 to image seasonal moisture dynamics on the hillslope scale. To link water content and electrical resistivity, the parameters of Archie's law were determined using different core samples. To optimize inversion parameters and methods, the derived spatial and temporal water content distribution was compared to tensiometer data. The results from ERT measurements show a strong correlation with the hydrometric data. The response is congruent to the soil tension data. Water content calculated from the ERT profile shows similar variations as that of water content from soil moisture sensors. Consequently, soil moisture dynamics on the hillslope scale may be determined not only by expensive invasive punctual hydrometric measurements, but also by minimally invasive time-lapse ERT, provided that pedo-/petrophysical relationships are known. Since ERT integrates larger spatial scales, a combination with hydrometric point measurements improves the understanding of the ongoing hydrological processes and better suits identification of heterogeneities.
- ItemThe role of spatial variability of soil moisture for modelling surface runoff generation at the small catchment scale(Göttingen : Copernicus GmbH, 1999) Bronstert, A.; Bárdossy, A.The effects of spatial variability of soil moisture on surface runoff generation at the hillslope and small catchment scale were studied. The model used is physically based accounting for the relevant hydrological processes during storm runoff periods. A case study investigating the effects on runoff generation in a loessy small catchment is presented. In this study the storm rainfall response was modelled using different distribution patterns of the initial soil moisture content, and where different initial soil moisture fields were generated by using both interpolation methods and stochastic simulation methods. It is shown that spatial variability of pre-event soil moisture results in an increase in runoff production compared to averaged values. It is of particular importance to note the combined organised/stochastic variability features, that is, the superposition of systematic and random features of soil moisture dominate local generation of surface runoff. In general one can say that the stronger the organised heterogeneity is, the more important is an adequate and refined interpolation technique which is capable of accounting for complex spatial trends. The effects of soil moisture variations are of particular importance for storms, where the produced runoff volume is just a small fraction of precipitation.
- ItemClimate-driven interannual variability of water scarcity in food production potential: A global analysis(Göttingen : Copernicus GmbH, 2014) Kummu, M.; Gerten, D.; Heinke, J.; Konzmann, M.; Varis, O.Interannual climatic and hydrologic variability has been substantial during the past decades in many regions. While climate variability and its impacts on precipitation and soil moisture have been studied intensively, less is known on subsequent implications for global food production. In this paper we quantify effects of hydroclimatic variability on global "green" and "blue" water availability and demand in global agriculture, and thus complement former studies that have focused merely on long-term averages. Moreover, we assess some options to overcome chronic or sporadic water scarcity. The analysis is based on historical climate forcing data sets over the period 1977-2006, while demography, diet composition and land use are fixed to reference conditions (year 2000). In doing so, we isolate the effect of interannual hydroclimatic variability from other factors that drive food production. We analyse the potential of food production units (FPUs) to produce a reference diet for their inhabitants (3000 kcal cap-1 day -1, with 80% vegetal food and 20% animal products). We applied the LPJmL vegetation and hydrology model to calculate the variation in green-blue water availability and the water requirements to produce that very diet. An FPU was considered water scarce if its water availability was not sufficient to produce the diet (i.e. assuming food self-sufficiency to estimate dependency on trade from elsewhere). We found that 24% of the world's population lives in chronically water-scarce FPUs (i.e. water is scarce every year), while an additional 19% live under occasional water scarcity (water is scarce in some years). Among these 2.6 billion people altogether, 55% would have to rely on international trade to reach the reference diet, while for 24% domestic trade would be enough. For the remaining 21% of the population exposed to some degree of water scarcity, local food storage and/or intermittent trade would be enough to secure the reference diet over the occasional dry years.
- ItemEvaluating Experimental Design of ERT for Soil Moisture Monitoring in Contour Hedgerow Intercropping Systems(Hoboken, NJ : Wiley, 2012) Garré, S.; Günther, T.; Diels, J.; Vanderborght, J.Contour hedgerow intercropping systems have been proposed as an alternative to traditional agricultural practice with a single crop, as they are effective in reducing run-off and soil erosion. However, competition for water and nutrients between crops and associated hedgerows may reduce the overall performance of these systems. To get a more detailed understanding of the competition for water, spatially resolved monitoring of soil water contents in the soil-plant-atmosphere system is necessary. Electrical resistivity tomography (ERT) is potentially a valuable technique to monitor changes in soil moisture in space and time. In this study, the performance of different ERT electrode arrays to detect the soil moisture dynamics in a mono- and an intercropping system was tested. Their performance was analyzed based on a synthetic study using geophysical measures, such as data recovery and resolution, and using spatial statistics of retrieved water content, such as an adjusted coefficient of variation and semivariances. The synthetic ERT measurements detected differences between the cropping systems and retrieved spatial structure of the soil moisture distribution, but the variance and semivariance were underestimated. Sharp water content contrasts between horizons or in the neighborhood of a root water uptake bulb were smoothened. The addition of electrodes deeper in the soil improved the performance, but sometimes only marginally. ERT is therefore a valuable tool for soil moisture monitoring in the field under different cropping systems if an electrode array is used which can resolve the patterns expected to be present in the medium. The use of spatial statistics allowed to not only identify the overall model recovery, but also to quantify the recovery of spatial structures.
- ItemModel-based reconstruction and projections of soil moisture anomalies and crop losses in Poland(Wien [u.a.] : Springer, 2020) Piniewski, Mikołaj; Marcinkowski, Paweł; O’Keeffe, Joanna; Szcześniak, Mateusz; Nieróbca, Anna; Kozyra, Jerzy; Kundzewicz, Zbigniew W.; Okruszko, TomaszEvidence shows that soil moisture (SM) anomalies (deficits or excesses) are the key factor affecting crop yield in rain-fed agriculture. Over last decades, Poland has faced several major droughts and at least one major soil moisture excess event leading to severe crop losses. This study aims to simulate the multi-annual variability of SM anomalies in Poland, using a process-based SWAT model and to assess the effect of climate change on future extreme SM conditions, potentially affecting crop yields in Poland. A crop-specific indicator based on simulated daily soil moisture content for the critical development stages of investigated crops (winter cereals, spring cereals, potato and maize) was designed, evaluated for past conditions against empirical crop-weather indices (CWIs), and applied for studying future climate conditions. The study used an ensemble of nine bias-corrected EURO-CORDEX projections for two future horizons: 2021–2050 and 2071–2100 under two Representative Concentration Pathways: RCP4.5 and 8.5. Historical simulation results showed that SWAT was capable of capturing major SM deficit and excess episodes for different crops in Poland. For spring cereals, potato and maize, despite a large model spread, projections generally showed increase of severity of soil moisture deficits, as well as of total area affected by them. Ensemble median fraction of land with extreme soil moisture deficits, occupied by each of these crops, is projected to at least double in size. The signals of change in soil moisture excesses for potato and maize were more dependent on selection of RCP and future horizon. © 2020, The Author(s).