How do you personally and professionally relate to water and/or space technologies?
My current research, previous work, and interest are centred around water. I am currently researching how radar-based satellite technology can be used to accurately identify flood areas and, over time, areas that are prone to flooding. My interest in this research was partly informed by work experiences where I was part of a team tasked with setting up early warning systems for communities living along rivers with an annual risk of flooding in Malawi. The need to understand more about floods and how to better prepare for them was also a result of witnessing annual flooding in a region downstream from where I grew up in western Kenya. For these reasons, I am motivated to find ways in which remote sensing, GIS, and other datasets can be used to reduce the impacts of flood disasters in vulnerable regions by understanding the magnitude of past recorded events.
Can you tell us about your current research on the use of Synthetic Aperture Radar (SAR) in mapping floods?
Currently, I am researching how to use statistical methods to identify flood mapping techniques that provide the highest accuracy in detecting open floods and floods under vegetation. I am leveraging the availability of vast historical Sentinel-1 SAR data to determine the best dual polarimetric change detection methods or a combination of methods that separates flood areas from non-flood areas. For open flooding, my primary study location is in the Forth Valley in Scotland, while the second study site, which focuses on inundated vegetation, is in Guyana. In Scotland, the findings of my research will enable rapid flood damage assessment and can be used to update flood risk maps. In Guyana, the analysis of annual flooding patterns and timings will inform the planned road infrastructure design. The findings will be key in identifying areas where road development will obstruct flood water movement, significantly impacting the biodiversity that depends on the annual flooding.
Please explain how the Polarimetric Synthetic Aperture Radar (PolSAR) works. What are the advantages in comparison to SAR?
Polarimetric Synthetic Aperture Radar (PolSAR) is an advanced form of Synthetic Aperture Radar (SAR) that provides more detailed information about the target being studied. While SAR systems are active remote sensing imaging techniques that rely on the backscatter signal recorded by the antenna compared to the signal sent out, PolSAR goes a step further. It analyzes the polarization state of the incident wave and the amount of backscattered energy to gather information about the target. The backscattered signals depend on various factors such as wavelengths, the characteristics of the imaged features, water content, roughness, or polarization. Traditional SAR methods focus on the amount of energy backscattered, but PolSAR provides additional insights by quantifying the scattering mechanisms exhibited by the target. This enables the differentiation of various features such as vegetation, surfaces, water, and urban areas. In summary, PolSAR offers a more comprehensive understanding of the target by analyzing the polarization state and backscattered energy, making it a valuable tool for distinguishing different features in remote sensing applications.
You used radar polarimetric data for detecting water hyacinth infestation in Lake Victoria. Can you share your main findings? What were the challenges?
In our study to understand the temporal variation of water hyacinth in the Winam Gulf of Lake Victoria, we found that Synthetic Aperture Radar (SAR) can effectively monitor trends in emergent vegetation on inland water bodies. By using polarimetric change detection methods, we achieved high accuracy in detecting water hyacinth, thanks to the cloud-penetrating capabilities of SAR systems. Our analysis revealed that the area covered by water hyacinth varied significantly over time and space. For instance, in November 2018, over 200 square kilometres of the lake were covered by water hyacinth, which gradually reduced to less than 1 square kilometre by October of the following year. Despite the high accuracy of these detections, distinguishing water hyacinth from other opportunistic vegetation within the colonies remained a challenge.
You worked as a hydrologist with SERVIR Eastern and Southern Africa project at the Regional Centre for Mapping of Resources for Development in Nairobi, Kenya. Can you tell us more about this project?
The SERVIR Project aimed to support various institutions in decision-making through the use of Earth Observation data. Organized into thematic areas such as water and water-related disasters, agriculture and food security, land use and land cover, and weather and climate, each thematic area developed tools, built the capacity of agencies, and supported the direct application of data to inform key decisions. As a USAID-NASA led initiative, there was significant technical expertise and support for developing new and innovative tools to assist agencies in Member States. For instance, as a hydrologist working under the water and water-related disasters theme, I was involved in developing an operational hydrological model that leveraged Earth observation data and climate forcings to determine water levels along points of ungauged rivers in Tanzania.
You were the Lead Hydrologist in the implementation of flood early warning using the Community Based Flood Early Warning System (CBFEWS) in Malawi. Can you tell us about how this system works? How did you integrate satellite technology into the system?
The Community Based Flood Early Warning System (CBFEWS) integrates telemetric water level measuring devices that record water levels every 5 minutes and relay this data to a cloud-based server. The server is configured to monitor these levels and is calibrated with specific alert thresholds. If these pre-determined alert levels are exceeded, a warning or alert is triggered to notify communities living downstream of potential floods. Within these communities, an alarm system was installed that can be manually-, SMS-, or server-triggered once a warning is verified. These warnings are calibrated to provide at least one hour of lead time for communities to evacuate. Communities are at the centre of this system, fostering collaboration between upstream and downstream communities to verify and validate warnings. Since the telemetric systems operate in near real-time, the GEOGLOWS hydrological model, which uses meteorological and satellite data forcings, is integrated into this system. The forecast provides discharge predictions for points along a river with a 15-day outlook. We incorporated a 5-day forecast to enable advanced monitoring of flood risks, which is confirmed or invalidated when the telemetric system records data. The discharge forecasts are converted into water levels, making it easier for communities to understand. This forecast enables early action activities.
You led the development of an operational hydrological model for basins in Tanzania. Can you explain how Earth observation (EO) is used for hydrologic modelling? Also, specifically for this project?
Earth observation data such as Digital Elevation Models, land use and land cover data, and other satellite-derived products like precipitation, wind speed, and direction can be used as forcings in a hydrological model to quantify/simulate hydrological conditions of a catchment or a river system. In Rufiji and Wami-Ruvu basins in Tanzania, I led the setup of the Variable Infiltration Capacity (VIC) model, a large-scale hydrological model, to support basin water officers in making water-related decisions by filling water data gaps using outputs from the model. The VIC model used static input data such as soil, terrain data, satellite-derived land cover data (MODIS), CHIRPS precipitation data, and ERA5 wind and temperature data to simulate runoff at specific stream locations of interest. The outputs from this model were continuous water level data. Water indices were computed to show the amount of water that can be allocated for different ecosystem services such as environmental flow, domestic use, or irrigation. Ultimately, this was meant to improve decision-making on water resources allocation in the basins.
Please discuss the need of a water stewardship program in Kenya.
Water stewardship is the responsible use and management of water resources in a way that is socially equitable, environmentally sustainable, and economically beneficial. Kenya faces escalating water risks due to deforestation, land degradation, and climate change, especially in areas like the River Nzoia Basin. A water stewardship program is needed to unite stakeholders through transparent, inclusive, and accountable actions, ensuring sustainable water use and long-term resilience in the face of increasing water stress.
What do you need to innovate?
To innovate, several key elements are essential. These include access to advanced technology such as Earth observation and remote sensing tools, which enable accurate and comprehensive data collection. Collaboration with diverse teams and experts brings fresh perspectives on different challenges. Additionally, a supportive environment and continuous learning are crucial for fostering innovation.
What is your favourite aggregate state of water?
My favourite aggregate state of water is liquid. A significant percentage of all water exists in this state, and I am always fascinated by its ability to support life in both fresh and saline environments. In saline states, such as in oceans, there are countless lives dependent on it. Liquid water is also the state that most, if not all, life uptakes and depends upon for survival.
