Browsing by Subject "Niederschlag"

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Adaption to rainfall and temperature variability through integration of mungbean in maize cropping
(2021) Khongdee, Nuttapon; Cadisch, Georg
Climate change has threatened global agricultural activities, particularly in tropical and subtropical regions. Rainfed cropping regions have become under more intense risk of crop yield loss and crop failure, especially in upland areas which are also prone to soil erosion. In Thailand, maize is one of the important economic crops and mostly grown in upland areas of northern regions. Maize yield productivity largely depends on the onset of seasonal rainfall. Uncertainty of seasonal rainfall adversely affects maize yield productivity. Therefore, coping strategies are urgently needed to stabilize maize yields under climate variability. In order to identify suitable coping strategies, early maize sowing and maize and mungbean relay cropping were tested on upland fields of northern Thailand. The specific aims of this thesis were (i) monitoring growth and yield performance of maize and mungbean under relay cropping, (ii) testing early maize sowing and maize – mungbean relay cropping as coping strategies under rainfall variations (Chapter 2), (iii) testing effects of relay cropping on growth and yield of mungbean under weather variability (Chapter 4), (iv) determining suitable sowing dates under erratic rainfall patterns by using a modelling approach (Chapter 3), and (v) developing a technique for diagnosis of crop water stress in maize by thermal imaging technique (Chapter 5). Specifically, in Chapter 2 early maize planting or relay cropping strategies were assessed for growth and yield performance of maize under heat and drought conditions. Maize planted in July showed, regardless of sole or relay cropping, low grain formation as a consequence of adverse weather conditions during generative growth. However, July-planted maize relay cropping produced higher above ground biomass than July-planted maize sole cropping and early planting of maize in June. Despite unfavourable weather conditions, maize was, at least partly, able to compensate for such effects when relayed cropped, achieving a higher yield compared to maize sole cropping. June-planted maize sole cropping, however, was fully able to escape such a critical phase and achieved the highest grain yield (8.5 Mg ha-1); however, its associated risk with insufficient rain after early rain spells needs to be considered. Relay cropping showed to be an alternative coping strategy to cope with extreme weather as compared to maize sole cropping. However, relay cropping reduced maize growth due to light competition at young stages of maize before mungbean was harvested (Chapter 2). This negative impact of relay cropping is partly off-set by considering of land equivalent ratio (Chapter 4). Land equivalent ratio indicated a beneficial effect of relay cropping over maize and mungbean solecropping (LER = 2.26). During high precipitation, mungbean sole cropping produced higher yield (1.3 Mg ha-1) than mungbean relay cropping (0.7 Mg ha-1). In contrast to the period of low precipitation, mungbean relay cropping used available water more efficiently and was able to establish its plant, while mungbean sole cropping could not fully withstand severe drought and heat. Mulching effects of maize residues conserved soil water which was then available for mungbean to grow under extreme weather condition. WaNuLCAS modelling approaches can be used to support the decision of maize sowing date in northern Thailand to cope with climate change as indicated by goodness of fit of the model validation (R2 = 0.83, EF = -0.61, RMSE = 0.14, ME = 0.16, CRM = 0.02 and CD = 0.56) (Chapter 3) using forty-eight-year of historical rainfall patterns of Phitsanulok province. Only 27.1% of rainfall probability was classified as a normal rainfall condition. Consequently, maize in this region had faced with high rainfall variability. From long term simulation runs, the current maize sowing date led to strong maize yield variation depending on rainfall condition. Early maize sowing i.e. 15 and 30 days before farmers and staggered planting produced higher yield than current farmers’ practice (mid of July) in most conditions (91.7%). Simulations revealed that water was the most limiting factor affecting maize growth and yield while nutrients (N and P) had only limited impact. Results of the WaNuLCAS model could be used to identify optimal maize planting date in the area prone to soil erosion and climate variation of northern Thailand; however, the model cannot fully account for heat stress. Thermal imaging technique is a useful method for diagnose maize water status. As presented in chapter 5, the developed Crop Water Stress Index (CWSI) using a new approach of wet/dry references revealed a strong relationship between CWSI and stomatal conductance (R2 = 0.82). Our study results established a linear relationship to predict final maize grain yield and CWSI values at 55 DAS as follows “Yield = -16.05×CWSI55DAS + 9.646”. Both early planting of maize and/or relay cropping with legumes are suitable coping strategies for rainfall variability prone regions. The positive response of early planting and legume relay cropping offers the opportunity of having a short-duration crop as sequential crop, providing an additional source of protein for humans and fostering crop diversification on-site. This leads to a win-win situation for farmers, food security and the environment due to an enhanced sustainability of this cropping system.
Model evaluation and data assimilation impact studies in the framework of COPS
(2012) Schwitalla, Thomas; Wulfmeyer, Volker
The goal of this thesis was the study of new approaches for improving and investigating quantitative precipitation forecasting (QPF), e.g., by optimizing model resolution, physics combination, and data assimilation. A forecasting system based on the Mesoscale Model 5 (MM5) was compared against other operational numerical weather prediction models from Meteo France, MeteoSwiss and the German Weather Service primarily with respect to daytime precipitation. First, a notable daytime dry bias was observed. It appears to be the result of a too small high-resolution domain and the switched-off convection parameterization from the second to the innermost domain. Even the application of a 4-dimensional variational data assimilation (4DVAR) with GPS slant total delays (STD) does not solve this problem due to inconsistent model physics between the 4DVAR and the forecasting model. Nevertheless, the MM5 is in good agreement with the shape of the observed diurnal cycle after the spin-up phase. As the development of the MM5 was suspended, a transition to the new Weather Research and Forecasting (WRF) model system was made after the D-PHASE period (end of 2007). This system features state-of-the-art physics packages and also a variational data assimilation system. As a new observing system, GPS Zenith Total Delay (ZTD) data from Central Europe were incorporated into the 3-dimensional variational data assimilation (3DVAR) system to further improve the initial water vapor field. A first study with this system revealed an improvement of the integrated water vapor RMSE of about 15% and a small but positive impact on the spatial and quantitative precipitation forecast. Additionally, the importance of assimilating upper air observations and the necessity to select a large, convection permitting model domain emerged. Finally a rapid update cycle (RUC) approach, comparable to operational forecast centers, has been developed for a convection-permitting configuration of the WRF model. The system is capable to assimilate radar observations from Germany and France, GPS-ZTD data and satellite radiances and can be applied even for near real-time applications. First experiments with this system show promising results in comparison to other operational models.
Untersuchungen zur räumlichen Heterogenität von Kronenstruktur und Bestandesniederschlag in einem tropischen Bergregenwald
(2008) Oesker, Mathias; Küppers, Manfred
The objective of this study was to investigate the distribution and heterogeneity of canopy structure and precipitation throughfall and related with this the factors light, water, and nutrient input. Further to appraise the consequences of this heterogeneity as a factor, which forms ecological niches. The study took place in a tropical mountain rain forest in southern Ecuador, specifically in the Reserva San Francisco located north of the Podocarpus National Park. The area of research covered the altitudinal range from 1950 m a.s.l. to 2275 m a.s.l. Nine plots of 400 m2 (20 m by 20 m) were set up in three forest types, which differed in tree species composition (HOMEIER 2004). Two forest types were located on a ridge and one was in a gorge at the same elevation as the lower ridge forest type. In each forest type three representative plots were chosen and a total of 31 study points were defined. At each point throughfall was collected during a one-year period. In all throughfall samples the following parameters were determined: Volume, pH, electrical conductivity, concentration of K, Mg and Ca, nitrate, ammonium, organic nitrogen, phosphate, P, Mn, Cu, Rb, Sr and Pb. The canopy structure was determined at all points with both structural measurements and hemispherical photography over a period of three years. Lab experiments with a representative selection of tree species were performed in order to determine leaf surface water storage capacity and nutrient leaching out of leaves. For determination of canopy structure hemispherical photography turned out to be a particularly efficient method. The software HemiView (DeltaT) was used to calculate important information such as canopy openness, light environment and LAI. A high spatial heterogeneity with a coefficient of variation (CV) of 59 % was found for all parameters. It was higher than the temporal variability over three years (CV 12 %). The throughfall was most heterogeneous within the investigated parameter with a CV of 64 %. In total close to 82 % (between 0.5 % and 492 % and a CV 29 %) of the volume of the incident precipitation could be collected as throughfall in the forest. With this throughfall 49.1 kg ha-1 a-1 K, 3.7 kg ha-1 a-1 Mg and 8.7 kg ha-1 a-1 Ca (mean values) were transported. During low intensity rain events the proportion of throughfall, expressed as percentage of incident throughfall was significantly lower than the annual mean of the incident precipitation. For high rain intensities no differences were found. With a geostatistical approach to investigate the spatial distribution of the throughfall no clear results could be calculated because the three replicates diverged strongly from each other. Canopy structure and its species composition was influenced by the distribution of throughfall. Related to the amount of throughfall it could be shown that with an open canopy up to 100 % of the incident precipitation could be collected. Underneath a closed canopy, in average less throughfall was collected. However, the volume of throughfall showed high spatial distribution and heterogeneity with even more than 100 % of incident precipitation. Nevertheless, throughfall volume can be predicted using the parameters radiation and canopy openness at a zenith angle of 36°. Average water storage capacity of leaf surfaces from eleven most common tree species resulted in 74.74 ml m-2 leaf area. In a dry canopy with a theoretical equal distribution of precipitation and a given LAI this value equals 0.38 mm of rain. The nutrient leaching out of leaves is species dependent and differs statistically. Those lab results can be extrapolated to the entire forest: Including the water storage capacity and the number of rain events, a maximum leaching capacity of 220 kg ha-1 a-1 K, 14 kg ha-1 a-1 Mg and 67 kg ha-1 a-1 Ca can be calculated. The main focus of this study was to investigate heterogeneity of abiotic factors and its ecological consequences. In the forest type with the most heterogeneous canopy structure and the most heterogeneous distribution of throughfall amounts were found. Lowest heterogeneity of spatial distribution of throughfall element contents was found in forest type with the lowest tree species diversity. The higher the tree species diversity the more heterogeneously scattered is the element content in the throughfall.