All seminars online. Please contact sue.davis@nottingham.ac.uk for the link. Subject to change.
Part of the Geosciences Seminar Series.
Laura Hunt
Assessing the potential of stable isotopes as hydroclimatic indicators in Ugandan crater lakes
A group of >80 crater lakes in western Uganda, associated with the East African Rift Valley, supply important water resources to rural communities, but face increasing pressure from human impacts and projected future climate change. By understanding the response of the lakes to past drivers of hydrological change, it is possible to forecast their responses to future scenarios, thus helping inform sustainable future management of surface water supplies.
In the absence of long-term instrumental monitoring of the lakes this project adopts a palaeolimnological approach. Previous studies from the region suggest that the lakes have experienced significant shifts in water quality during the late Holocene (Bessems et al., 2008; Mills et al., 2014; Mills et al., 2018; Ryves et al., 2011; Ssemmanda et al., 2005), but changes in water quantity are relatively poorly understood. In this seminar, I present new carbonate oxygen and carbon stable isotope records from two crater lakes, alongside data from a modern lake survey, that are used to aid the interpretation of the stratigraphic records. Preliminary findings show that the regions lakes do not have a uniform response to climate and catchment change. The seminar will also outline the approaches to be taken in the rest of the PhD to try and explain these differing responses.
Abdulaziz Alsaleh
A hydrological and geomorphological investigation of Riyadh city, Saudi Arabia
Riyadh City has dramatically expanded from 42 km2 in 1976 to over 1,500 km2 in 2020. There are two main river catchments in the city (Wadi Hanifah and Wadi As Silayy). The hydrological and geomorphological implications of this rapid development have not been suitably considered in the past and future planning of Riyadh. The expansion of Riyadh has been mainly based on a grid street system and the homogenisation of the land surface through the destruction of landforms. For example, dry valleys and ephemeral stream channels have been blocked and hills have been levelled or extremely modified resulting in serious environmental problems like flooding. There have also been significant changes in land-use.
A literature search revealed that no studies have previously investigated the changing geomorphology of Riyadh and very little work has explored the effects of changing land-use on surface runoff. Therefore, the main aim of this PhD research is to provide new information on geomorphology, rainfall, and runoff for Riyadh within the context of changing land-use patterns. The main achievements of the research so far include the production of a comprehensive literature review, the validation and calibration of a complex and comprehensive SWAT model for Riyadh and the generation of a medium scale generalized geomorphological map.
There is little hydrological data available for the Riyadh region, including no data on observed river flows, so substantial effort was placed in developing a SWAT model that could be calibrated and validated on evapotranspiration data from TerraClimate Earth Observation data. The calibration and validation exercise showed that the model performs well. The NSE and R2 results for the Wadi Hanifa basin are 0.49 and 0.56 respectively, while the NSE 0.60 and the R2 0.63 for the Wadi As Silayy.
The developed geomorphological map covers an area of approximately 5,000 km2 and currently about 31% of the mapped area is covered by developments. This is expected to change with future land-use change patterns. The generation process of the map depended mainly on visual interpretation of historical aerial photographs and Landsat images, preceded by a reconnaissance field visit and with aid of available geologic, topographic maps and high-resolution multi-temporal images. The geomorphological map presents the distribution of five geomorphological units which are cuestas, pediplains, hills and pediments, alluvial deposits, and sand fields.
The next stage of the PhD is to intensify the efforts to complete SWAT modelling on land use change, data analysis, to get the remaining results, and to write the chapters of the thesis.