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Observational evidence and future climate change scenarios suggest an amplification of climatic contrasts across the UK. This is seen most prominently in the marked increase in notable flood events and drought episodes and may profoundly affect water resource systems in vulnerable areas, as exemplified by the 1995 Yorkshire drought. The 1995-96 drought resulted in severe stress to the Yorkshire water supply, necessitating the emergency measure of tanking in water from outside the region, and was caused by an unusual pattern of weather and precipitation. This research is an investigation into both natural climatic variability and possible future climate change in Yorkshire aiming to quantify the risk of future occurrence of severe drought events, such as that of 1995. Historical drought characteristics and spatial-temporal precipitation variability in Yorkshire are examined and linked to synoptic weather patterns. A multi-site stochastic rainfall model is then developed using conditioning by synoptic weather types. The model can account for spatial variability and allows the concurrent simulation of precipitation time-series for very different climatological sub-regions within the same water resource area. This model is used to investigate the impact of natural climatic variability and possible future climate change upon water resource reliability, resilience and vulnerability in Yorkshire. The structure of the stochastic rainfall model enables the impact of variations in weather type persistence or frequency to be investigated. In addition, rainfall model statistics can be altered to simulate instances of increased precipitation intensity or proportion dry days for example, for individual weather groups. The UKCIP98 Medium-High climate change scenarios for 2021- 2050 and 205 1-2080 are investigated using modifications to weather type frequency, precipitation and potential evapotranspiration. Results indicate that water resources in Yorkshire are likely to become more reliable on average under the examined climate change scenarios due to increased winter precipitation. However, model simulations also suggest a reduction in resource resilience and increased vulnerability to drought. Severe droughts comparable to that of 1995 show only a slight increase in frequency by 2080. However, there will be a significant increase in both magnitude and duration of severe drought, as a consequence of summer precipitation reductions and increased climatic variability. This methodology of simulating the impacts of potential atmospheric circulation change on precipitation regimes can provide a basis for the future planning and management of water resource systems.

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Doctor of Philosophy / Department of Agronomy / P. V. Vara Prasad / Drought and high temperature are major detriments to global wheat production. Wheat varies in its susceptibility to drought and high temperature stress. Three experiments were performed to address the challenges of drought and high temperature stress in wheat. The first experiment consisted of 256 genotypes of spring wheat and 301 genotypes of winter wheat, field screened for yield traits related to drought tolerance, in irrigated and dryland experiments. The experimental designs for the first experiment were both augmented incomplete block designs with one-way or row-column blocking. This experiment was performed at the Ashland Bottom Research Farm, south of Manhattan, KS, between 2011-2013. From this experiment, three conclusions were made: wheat genotypes vary widely in their responses between dryland and irrigated treatments and this variation can be used in future experiments or breeding tolerant genotypes. The number of seeds per unit of area, total biomass per unit area, and the average weight of one thousand seeds, were the best yield traits for predicting yield in both irrigated and dryland environments. Twenty genotypes were selected for future research based on their susceptibility or tolerance to drought. The second experiment was performed in the greenhouse facilities to observe the source-sink relationship of spring wheat genotype Seri 82 under drought and defoliation. The experiment was a randomized complete block design with a split-plot treatment arrangement. Post-anthesis cessation of watering and defoliation were the treatments. Both water stress and defoliation affected seed yield and total biomass. The major effect of post-anthesis water stress was a decrease in single seed weight. Defoliation affected the source-sink relationship by reducing the source strength of the leaves. This caused the stem to contribute more to overall yield. The defoliation also caused the remaining leaves to compensate for the removed leaves. The final experiment evaluated the changes in seed-filling rate and duration of three winter wheat genotypes during high temperature stress. High temperature stress reduced the duration of seed fill and increased the rate, differently in each genotype. Higher yields in the winter wheat growing regions, susceptible to post-anthesis high temperature stress, may be possible through selection of cultivars with faster seed-filling rates and/or duration of seed filling.

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>Magister Scientiae - MSc / Food security has always been one of the priority concerns in Africa, and it is mostly threatened by drought stress due to climate change. Drought-induced stress is one of the serious limiting factors of plant production, and it is known to impose oxidative stress as a consequence of excessive reactive oxygen species (ROS) accumulation that lead to lipid peroxidation, which is manifested as increased cell death. Hence, this study investigated the influence of drought stress on two contrasting canola genotypes (Agamax and Garnet), by monitoring their physiological and molecular changes. The results showed that the plant growth and biomass of both genotypes were significantly affected by drought stress as a consequence of excessive ROS accumulation (manifested as H₂O₂ and OH· content). However, under drought stress conditions, the reduction in biomass and shoot length was more pronounced in the Garnet genotype when compared to that of the Agamax genotype. This was further supported by the increase in lipid peroxidation and cell death, which were shown to be significantly higher in the Garnet genotype when compared to the Agamax genotype under drought stress. ROS scavenging ability which prevents oxidative stress and ultimately ROS-induced cellular damage. Hence, given the higher levels of antioxidant activity coupled with the reduction in ROS accumulation that was observed in the Agamax genotype, we suggest that the Agamax genotype might be slightly less susceptible to drought stress, when compared to the Garnet genotype. Furthermore, understanding the proteomic responses of these two contrasting genotypes that showed a marked difference in response to drought stress might help in unlocking complex biological networks of proteins underlying drought stress tolerance. Hence we use two-dimensional (2D) gel electrophoresis coupled with Matrix assisted laser desorption/ionisation-time of flight/time of flight tandem mass spectrometry (MALDI TOFTOF MS) analysis for this part of the study, in order to detect and analyze those differentially expressed proteins or proteins whose abundance levels were influenced as a consequence of drought stress. To gain additional insight into the leaf proteomes of the two canola genotypes, a protamine sulphate precipitation (PSP) method was used to remove RuBisCo and confirmed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) analysis. A total of 55 well resolved protein spots were selected for mass spectrometry analysis of which 31 (56%) were positively identified using the selective criteria analysis (SCA). All positively identified proteins were then classified into functional categories including protein folding (3%), photosynthetic (29%), detoxification and protection (20%), and energy related proteins whereas 16% could not be classified into any functional category. Apart from spot 32 (Fe superoxide dismutase) and spot 34 (chloroplast beta-carbonic anhydrase), no further significant difference in protein expression/abundance was observed for all the identified proteins for both genotypes in response to drought stress. Both proteins (spots 32 and 34) have been shown to contain antioxidant activity properties which suggest that they might play a crucial role in improving drought stress tolerance in canola plants.

Soil moisture available to crops is among the main constraints on crop production by smallholder farmers in semi-arid Zimbabwe. Other restrictions, such as limited use of fertilisers and herbicides, stem primarily from socio-economic rather than biophysical constraints. To improve smallholder farming, it is essential to promote soil and water conservation practices (SWC) that consider farmers' management constraints, such as limited availability of labour and Draught Animal Power (DAP).

Indiana University-Purdue University Indianapolis (IUPUI) / Water is fundamental for plant growth, and vegetation response to water availability influences water, carbon, and energy exchanges between land and atmosphere. Vegetation plays the most active role in water and carbon cycle of various ecosystems. Therefore, comprehensive evaluation of drought impact on vegetation productivity will play a critical role for better understanding the global water cycle under future climate conditions. In-situ meteorological measurements and the eddy covariance flux tower network, which provide meteorological data, and estimates of ecosystem productivity and respiration are remarkable tools to assess the impacts of drought on ecosystem carbon and water cycles. In regions with limited in-situ observations, remote sensing can be a very useful tool to monitor ecosystem drought status since it provides continuous observations of relevant variables linked to ecosystem function and the hydrologic cycle. However, the detailed understanding of ecosystem responses to drought is still lacking and it is challenging to quantify the impacts of drought on ecosystem carbon balance and several factors hinder our explicit understanding of the complex drought impacts. This dissertation addressed drought monitoring, ecosystem drought responses, trends of vegetation water constraint based on in-situ metrological observations, flux tower and multi-sensor remote sensing observations. This dissertation first developed a new integrated drought index applicable across diverse climate regions based on in-situ meteorological observations and multi-sensor remote sensing data, and another integrated drought index applicable across diverse climate regions only based on multi-sensor remote sensing data. The dissertation also evaluated the applicability of new satellite dataset (e.g., solar induced fluorescence, SIF) for responding to meteorological drought. Results show that satellite SIF data could have the potential to reflect meteorological drought, but the application should be limited to dry regions. The work in this dissertation also accessed changes in water constraint on global vegetation productivity, and quantified different drought dimensions on ecosystem productivity and respiration. Results indicate that a significant increase in vegetation water constraint over the last 30 years. The results highlighted the need for a more explicit consideration of the influence of water constraints on regional and global vegetation under a warming climate.

Forestry management relies on combating the challenges posed by fire. Knowledge of fire risk helps in the planning for and reacting to forest fires. One method used is the mapping of the Keetch-Byram Drought Index (KBDI). Though it was not specifically designed to be a fire risk assessment tool it is used to highlight areas with a high potential of fire due to climactic factors. A statistical analysis is performed to determine the relevance of the use of this drought index to measure fire potential. Analysis is performed by testing the relationship of KBDI to the number of fires and area burned in the Mississippi Forestry Commission?s south east fire district. These analyses showed a weak relationship between total fires and KBDI. In many cases there was no relationship. This calls into question the use of KBDI to determine fire potential.

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