A series of studies were conducted to examine the antioxidant status, drought and disease tolerance, and growth response to foliar application of soluble seaweed (Ascophyllum nodosum) extracts (SE) and humic acid (HA; 25% active HA or 2.9% active HA) in tall fescue (Festuca arundinacea Schreb), Kentucky bluegrass (Poa pratensis L.) and creeping bentgrass (Agrostis palusttis Huds.) grown under low (-0.5 MPa) and high (-0.03 MPa) soil moisture environments. Foliar application of humic acid (2.9 % active HA) at 23.7 and 47.4 l/ha improved leaf water status, shoot and root development in tall fescue, Kentucky bluegrass and creeping bentgrass grown under drought. Humic acid (2.9% active HA) at 15.5 l/ha or SE at 326 g/ha significantly reduced dollarspot incidence and improved turf quality in creeping bentgrass. Drought stress induced an increase of antioxidants alpha-tocopherol and ascorbic acid concentrations in the three turfgrass species. In the experiment with Kentucky bluegrass, drought stress increased beta-carotene concentration, but did not significantly influence superoxide dismutase (SOD) activity. Foliar application of humic acid (25% active HA) at 5 l/ha and/or SE at 326 g/ha consistently enhanced alpha-tocopherol and ascorbic acid concentrations, leaf water status, and growth in the three cool-season turfgrass species grown under low and high soil moisture environments. In the experiment with Kentucky bluegrass, application of HA at 5 l/ha plus SE at 326 g/ha also increased beta-carotene content and SOD activity under low and high soil moisture environments. There were close positive correlations between the antioxidant status and shoot or root growth in the three turfgrass species regardless of soil moisture levels. The antioxidant SOD activity, photosynthetic capacity in terms of Fvm690, and chlorophyll content in terms of Fm730/Fm690 exhibited a seasonal fluctuation in endophyte [Neotiphodium coenophialum (Morgan Jones and Gams) Glenn, Bacon, Price and Hanlin] -free and endophyte-infected tall fescue. Application of SE enhanced SOD activity, photosynthetic capacity, and chlorophyll content in tall fescue, especially at 4 weeks after SE treatment. The SOD activity, photosynthetic capacity and chlorophyll content were not significantly influenced by the endophyte infection. A close positive correlation between SOD and photosynthetic capacity during the summer was found in endophyte-free and endophyte-infected tall fescue. / Ph. D.

California has experienced an unusually dry past two decades punctuated by three intense multi-year droughts from 2007-2010, 2012-2015, and 2020-2022. A portion of the water lost during these two decades is due to intense groundwater overdraft of the Central Valley Aquifer. This groundwater overdraft has led to poroelastic compaction of the aquifer system and subsidence of the land surface. Water mass loss also causes elastic deformation of the solid Earth, an opposite and smaller amplitude response than the poroelastic deformation of aquifer systems. These mass changes can disturb the regional stress field, which may influence earthquake activity. Both the elastic and poroelastic deformation responses can be observed using satellite-based geodetic tools including Global Navigation Satellite System (GNSS) station displacements and Interferometric Synthetic Aperture Radar (InSAR). In this dissertation, I model aquifer-system compaction at depth using InSAR-based vertical land motion during the 2007-2010 drought and evaluate hazards related to Earth fissures, tensional cracks that form at the edges of subsidence zones. Next, I forward-calculate the predicted elastic deformation response to groundwater mass loss over the same period and calculate crustal stress change to evaluate what, if any, impact this has on seismicity in California. In addition to modeling deformation caused by water storage change, I also introduce a new method to jointly invert elastic vertical displacements at GNSS stations with water storage anomalies from the Gravity Recovery and Climate Experiment (GRACE) to solve for water storage changes from 2003-2016 over California. Finally, I expand on this joint inversion framework to include poroelastic deformation measured using InSAR over the Central Valley aquifer-system to solve for a change in water storage and groundwater storage over water years 2020-2021, the most recent drought period in California. / Doctor of Philosophy / Changes in the hydrologic system can have wide-reaching societal, geopolitical, economic, ecological, and agricultural impacts. Proper water management, particularly in places that have water scarcity concerns due to overuse, water pollution, or recurrent drought conditions, is essential to ensure this resource is available to future generations. Current projections of climate change scenarios point to more intense and frequent extreme hydroclimate events. With accelerating population growth in many urban centers across the world, measuring water storage changes has never been more important to ensure resiliency of our cities, energy sector, and agricultural systems. Furthermore, water storage changes deform the Earth, which may create or alter geophysical hazards such as subsidence, the development of Earth fissures, and seismicity. Today, a multitude of space-based geodetic tools allow us to monitor changes in the Earth system, including changes in terrestrial water content and associated deformation, with higher spatial and temporal resolution than ever before. These datasets have provided an unprecedented understanding of hydroclimatic hazards and have resolved constraints arising from sparse and infrequent in-situ measurements. Here, I use space-based geodetic tools and geophysical models to measure water storage fluctuations, deformation, and evaluate associated hazards in California, a region that has experienced an unprecedented nearly continuous two-decades long drought. In general, I find that 21st century droughts have caused significant water storage loss, especially groundwater storage loss, in California, which has exacerbated some geophysical hazards including land subsidence and Earth fissure hazards.

Coping with droughts involves two phases. In the first phase drought susceptibility of a region should be assessed for developing proper additional sources of supply which will be exploited during the course of a drought. The second phase focuses on the issuance of drought warnings and exercising mitigation measures during a drought . These kinds of information are extremely valuable to decision making authorities. In this dissertation three broad schemes i) time series modeling, ii) Markov chain analysis, and iii) dynamical systems approach are put forward for computing the drought parameters necessary for understanding the scope of the drought. These parameters include drought occurrence probabilities, duration of various drought severity classes which describe a region's drought susceptibility, and first times of arrival for non drought classes which signify times of relief for a drought-affected region. These schemes also predict drought based on given current conditions. In the time series analysis two classes of models; the fixed parameter and the time varying models are formulated. To overcome the bimodal behavior of the Pallner Drought Severity Index (PDSI), primarily due to the backtracking scheme to reset the temporary index values as the PDSI values, the models are fitted to the Z index in addition to the PDSI for the forecasting of the PDSI. / Ph. D.

Globally, it is expected that arid and semi-arid areas will face increasing frequency of drought through the 21st century. Drought is normally attributed to climatic factors. However, humans constantly alter hydrologic systems through manipulating and consuming water, which can also cause drought. However, human influence on drought, outside of influences on warming-driven climate change, is rarely studied. Here, the upper Colorado River Basin (Texas) is studied to assess the human influence on drought conditions in a semi-arid basin. An observation-modeling framework is used to simulate naturalized runoff conditions which are compared to observed data in an undisturbed (little human influence) and disturbed (much human influence) period to elucidate human influences on drought. Further, public water storage and supply data are incorporated to analyze how human water management may be specifically affecting downstream hydrologic drought in the upper Colorado River Basin. Results show that according to observed data, drought occurred more often, persisted longer on average, and had a higher maximum duration during the disturbed period. Naturalized model output did not predict such increases, indicating that human influence is responsible. Water deliveries in the study area were found to significantly affect downstream flow and are connected to instances of human-influenced drought. Results suggest that in order to reduce downstream drought conditions, deliveries will likely have to be reduced and that reducing deliveries during periods of low rainfall, or during months in which deliveries constitute a large portion of human influenced drought severity could be especially helpful in alleviating downstream drought. / Master of Science / It is expected that many arid climates around the globe will become even experience more frequent drought during the 21st century. Drought is a lack of water relative to normal levels and has important implications for agriculture, industry, fisheries, water managers, and the broader public. Drought is normally attributed to natural factors such as lack of rain or increases in temperature. Humans have affected these factors through global climate change, and many researchers have focused their efforts on understanding how global warming impacts drought conditions. However, humans can also affect drought conditions through water consumption. Despite the impact of human water consumption, it is rarely a topic of specific study in relation to the occurrence of drought. Here, conditions lacking human influence (i.e. no water consumption, land-use change, etc.) are simulated and compared to observed data from a stream gage downstream from human intervention, allowing for examination of human influences on drought. Public water usage and management data from the Colorado River Municipal Water District are also incorporated to allow for more specific understanding of how human influence affects drought conditions downstream of reservoir operation and groundwater pumping. Results show that drought occurred more often, persisted longer on average, and had a higher maximum duration due to human influence. Water usage and management by the Colorado River Municipal Water District are connected to and have a role in causing decreases in downstream flow and occurrence of drought. Results indicate that demand reductions will likely be needed to ensure sustainable water availability and that reducing demand during periods of low rainfall or during times of the year in which human water use accounts for larger portions of drought severity could be most helpful in lessening downstream drought.

Disasters have increased in frequency and their impact has been intensely felt on the continent. This frequently results in damage to the resources and infrastructure on which humans rely on for survival and quality of life. When disasters strike, large segments of the population are faced with devastating consequences, which include food shortages, limited shelter and inadequate health services. Disasters are a result of a complex mix of natural and other hazards, including human actions and vulnerabilities. They consist of a combination of factors that determine the potential for people to be exposed to particular types of hazards. The frequency and impact of disasters in South Africa has increased significantly, the most common type of disaster being drought. Droughts are the result of reduced amounts of rain received over a long period of time, but it includes delays at the beginning of the precipitation season that affects crops that depend on the rain. For the purpose of this study, agricultural and socioeconomic drought received attention. Agricultural drought is when the humidity in the soil is not sufficient to assist crop production and growth in the area. Socio-economic drought arises when economic activities aligned with other elements do not meet the population demand. Agricultural droughts often have the latent effect of reducing agricultural production to such an extent that the livelihoods of the communal farmers are threatened. Drought effects often result in shrivelling crops, loss of water resources, vegetation and a decrease in livestock forage for communal farmers. This, in turn, leads to a decreased availability of food and the overall loss of livelihoods. In addition, activities such as crop growing and grazing conditions for livestock remain vulnerable, yet rural communities rely on these to generate income. The most severe impact of droughts do not simply include the absence of food supply for the community, but rather correlates directly with the severity and the duration of droughts. This often increases the community’s vulnerability. The empirical findings were concluded from focus groups interviews and semistructured interviews as data collection for the study. The data collected from the field was compared to the Sustainable Livelihood Framework. The analysis revealed that drought mitigation in South Africa only exists in governmental policy documents. Moreover, the lack of a disaster management plan for Setlagole makes it difficult to prepare for drought. An inadequate relationship between farmers and the government also makes it difficult to create a sense of shared vision and mission for drought alleviation. One prominent issue that makes the effects of drought so severe is the process of relief; it takes too long for the government to give assistance to the farmers. This shows that mitigation measures are needed to prepare both the farmers and the government for drought. / M Development and Management, North-West University, Potchefstroom Campus, 2015

Disasters have increased in frequency and their impact has been intensely felt on the continent. This frequently results in damage to the resources and infrastructure on which humans rely on for survival and quality of life. When disasters strike, large segments of the population are faced with devastating consequences, which include food shortages, limited shelter and inadequate health services. Disasters are a result of a complex mix of natural and other hazards, including human actions and vulnerabilities. They consist of a combination of factors that determine the potential for people to be exposed to particular types of hazards. The frequency and impact of disasters in South Africa has increased significantly, the most common type of disaster being drought. Droughts are the result of reduced amounts of rain received over a long period of time, but it includes delays at the beginning of the precipitation season that affects crops that depend on the rain. For the purpose of this study, agricultural and socioeconomic drought received attention. Agricultural drought is when the humidity in the soil is not sufficient to assist crop production and growth in the area. Socio-economic drought arises when economic activities aligned with other elements do not meet the population demand. Agricultural droughts often have the latent effect of reducing agricultural production to such an extent that the livelihoods of the communal farmers are threatened. Drought effects often result in shrivelling crops, loss of water resources, vegetation and a decrease in livestock forage for communal farmers. This, in turn, leads to a decreased availability of food and the overall loss of livelihoods. In addition, activities such as crop growing and grazing conditions for livestock remain vulnerable, yet rural communities rely on these to generate income. The most severe impact of droughts do not simply include the absence of food supply for the community, but rather correlates directly with the severity and the duration of droughts. This often increases the community’s vulnerability. The empirical findings were concluded from focus groups interviews and semistructured interviews as data collection for the study. The data collected from the field was compared to the Sustainable Livelihood Framework. The analysis revealed that drought mitigation in South Africa only exists in governmental policy documents. Moreover, the lack of a disaster management plan for Setlagole makes it difficult to prepare for drought. An inadequate relationship between farmers and the government also makes it difficult to create a sense of shared vision and mission for drought alleviation. One prominent issue that makes the effects of drought so severe is the process of relief; it takes too long for the government to give assistance to the farmers. This shows that mitigation measures are needed to prepare both the farmers and the government for drought. / M Development and Management, North-West University, Potchefstroom Campus, 2015

Published Article / The objective of this study was to characterize meteorological droughts in the Central Region of South Africa, Modder River Basin, C52A quaternary catchment using two popular drought indices: Standardized Precipitation Index (SPI) and Standardized Precipitation-Evapotranspiration Index (SPEI) and to compare the two indices. Drought events were characterized based on their frequency, duration, magnitude and intensity. The indices were computed for the time-scales that are important for planning and management of water resources, i.e. 3-, 6- and 12-month time-scales. The basic meteorological input data used in the computation of these indices were 57 years (1950-2007) of monthly precipitation and monthly temperature data which were recorded at The Cliff weather station in the quaternary catchment. It was found that both SPI and SPEI responded to drought events in similar fashion in all time-scales. During the analysis period, a total of 37, 26 and 17 drought events were identified in the area based on 3-, 6-, and 12-month times-scales, respectively. Considering event magnitude as severity parameter, results from both indices identified the periods 1984-1985, 1992-1993 and 2003-2005 as the severest drought periods in the area. However, when the effects of both drought duration and magnitude are considered (drought intensity), the most severest drought events were identified during the years 1982/83, 1966 and 1973 based on 3-, 6- and 12-month timescales, respectively. It was concluded that although the SPEI generally exhibits veracity over SPI by including, apart from precipitation, additional meteorological parameter, mean temperature, SPI should be adopted as an appropriate drought monitoring tool in an area, like Africa, where meteorological data are scarce.

This dissertation investigates the spatio-temporal dynamics of intermittent stream fish metacommunities in response drought-induced fragmentation and re-connectivity using both field and experimental approaches. A detailed field study was conducted in two streams and included pre-drought, drought, and post-drought hydrological periods. Fish assemblages and metacommunity structure responded strongly to changes in hydrological conditions with dramatic declines in species richness and abundance during prolonged drought. Return of stream flows resulted in a trend toward recovery but ultimately assemblages failed to fully recover. Differential mortality, dispersal, recruitment among species indicates species specific responses to hydrologic fragmentation, connectivity, and habitat refugia. Two manipulative experiments tested the effects of drought conditions on realistic fish assemblages. Fishes responded strongly to drought conditions in which deeper pools acted as refugia, harboring greater numbers of fish. Variability in assemblage structure and movement patterns among stream pools indicated species specific habitat preferences in response predation, resource competition, and desiccation. Connecting stream flows mediated the impacts of drought conditions and metacommunity dynamics in both experiments. Results from field and experimental studies indicate that stream fish metacommunities are influenced by changes in hydrological conditions and that the timing, duration, and magnitude of drought-induced fragmentation and reconnecting stream flows have important consequences metacommunity dynamics.

Bibliography: leaves 187-216.

The economic feasibility of producing biomass-based fuels requires high-yielding feedstocks to supply biomass to biorefineries. Populus trees are a potential biomass feedstock due to their high yield, but their high water requirement limits productivity under drought conditions. The number of genes controlling drought tolerance, and the long generation time for perennial species, slows cultivar development. Accelerated domestication proposes using the sequenced Populus genome to quickly incorporate target traits into productive clones by transgenesis. Six putative drought tolerance transcription factors: DREB2A, DREB2B, AtMYB, AREB1/ABF2, MYB, and NAC, had been previously identified and manipulated in eastern cottonwood (Populus deltoides). Three constructs of each gene were transformed into a P. deltoides background clone, including constitutive overexpression (OE), drought inducible OE, and knockdown. This greenhouse study examines the effect of these previously transformed constructs on drought tolerance by characterizing leaf abscission, leaf water potential, and growth under drought and well-watered conditions. AREB1/ABF2 constitutive OE lost significantly fewer leaves under drought than the Vector control, and had one of the lowest rates of leaf loss overall. Both DREB2A inducible OE and AREB1/ABF2 constitutive OE plants were more productive than the Vector control under drought conditions. MYB inducible OE was a productive construct and initially appeared to be drought tolerant. It is possible that this construct experienced xylem cavitation early on due to the severity of drought experienced by the large trees containing this construct. DREB2A inducible OE, AREB1/ABF2 constitutive OE, and MYB inducible OE were the most productive constructs as well as being likely to confer drought tolerance. Field trials would be the next step, providing a clearer picture of how these constructs would perform under natural conditions.