The glaciers of the Cordillera Blanca Peru are rapidly retreating as a result of climate change, altering the timing, quantity and quality of water available to downstream users. Changes in water availability have serious implications for ecosystems, human livelihoods and regional economies. This dissertation investigates spatiotemporal changes in the glacier hydrologic system of the Cordillera Blanca Peru. It includes three major components. First, I develop multispectral unmanned aerial vehicles (UAV) and kite platforms capable of operating at over 5000m in mountain regions. Secondly, I deploy these platforms to investigate processes of glacier change and surface/subsurface hydrology within the glacial valleys of the Cordillera Blanca. Finally, I integrate UAV datasets with traditional field hydrology to improve our understanding of the spatiotemporal variability in soil moisture and its role in moderating groundwater storage within the Cordillera Blanca.
I designed and deployed UAVs on multiple missions at over 5000masl in the Cordillera Blanca, Peru. After describing the UAV design in Chapter 2, this dissertation reports on results of four studies that utilise the UAV to address research questions within the region. Chapter 3 comprehensively assesses the accuracy of photogrammetrically derived structure from motion (SfM) digital elevation models (DEMs), by quantitatively and qualitatively comparing the data against surveyed GPS positions and LiDAR DEMs. Finding that accuracy is as good if not superior to low density LiDAR, with the high density SfM point clouds retaining unique surface details. Chapter 4 investigates the dynamics of glacier change over the debris covered Llaca glacier. I document the importance of debris cover and surface features such as ice cliffs in controlling melt rates. Average glacier downwasting is 0.75m over one year but is highly heterogeneous. Ice cliff horizontal recession rates of up to 25m annual were measured illustrating the importance of debris thickness and ice exposure to the evolution of these systems. Only limited horizontal retreat of the glacier tongue was recorded, indicating that simple measurements of changes in aerial extent are inadequate for understanding actual changes in glacier ice quantity. In Chapter 5 I investigate spatial variability in surface soil moisture. By collecting multispectral (visible, near infrared and thermal infrared) imagery and using the temperature vegetation dryness index (TVDI) I generate 50cm pixel resolution estimates of soil moisture for two proglacial wetland/meadow study sites. Surface soil moisture is found to vary markedly over short distances and is negatively impacted by grazing practices. Through inspection of the multispectral UAV imagery I was able to identify surface and subsurface hydrologic pathways including groundwater springs from airborne thermal imagery. Finally in Chapter 6 I integrate the UAV findings with field instrumentation. I investigate spatiotemporal variability in soil moisture and groundwater table storage within the meadows and wetlands of the Cordillera Blanca. Key findings from the three study sites were the high rates of evapotranspiration, and the limited role of water stored in the groundwater table, and as soil moisture, in buffering dry season stream flow. However, the peatland soils were found to have very low bulk densities (~0.15g/cm3), and a high water storage capacity. Reaching 80-90% volumetric water content at saturation. Thus meadow and wetland systems in the Cordillera Blanca may still play an important role in reducing runoff and increasing groundwater recharge during the wet season, which is an important source of dry season stream flow.
My results show that UAVs are an ideal method for studying heterogeneous landscapes at high resolution, and are thus highly suited for small scale studies within mountain regions. This dissertation provides a double faceted scientific contribution of both methodological and technological advances in the ways in which UAV's can be used in earth science and high mountain research as well as empirical knowledge regarding the regional hydrology of the Cordillera Blanca and more generally the tropical Andes. Through its focus on water availability this research has important implications for rural livelihoods and long-term hydrologic, energy, economic and development planning in Peru. This research also contributes to the growing field of UAV applications by pushing the engineering boundaries of this technology, opening up a range of future scientific opportunities in other areas.