| Summary: | Research Doctorate - Doctor of Philosophy (PhD) In semiarid regions, a small variation in the solar insolation has a profound impact on the topography via the feedback mechanism among the hydrology, vegetation, sediment transport, and landscape evolution. The emergence of aspect-controlled vegetation patterns caused by solar insolation in semiarid ecosystems leads to differentiation in available soil moisture and vegetation characteristics on opposing hillslope aspects. Previous studies have shown that in mid- to high-latitudes where available soil moisture is a limiting factor for vegetation growth, polar-facing slopes (PFS) develop denser vegetation cover than equatorial-facing slopes (EFS). However, these studies have been limited by observations at the field or hillslope scale and do not reflect during the entire year. Some recent findings have challenged this common paradigm and have shown that there may occur a seasonal reversal of vegetation greenness across opposing hillslopes in semiarid regions. In addition, transitions in vegetation patterns in semiarid landscapes can influence the dominant erosion processes on opposing hillslopes and result in hillslope asymmetry. This research aimed to explore different eco-hydro-geomorphic processes in the semiarid ecosystems, especially with aspect control. This research started by studying 60 catchments from 23 different locations from all continents, except Antarctica, to identify the vegetation greenness patterns across opposing hillslopes. The normalised differences vegetation index (NDVI) was used as a proxy for the vegetation greenness in catchments. A total of 18 years of mean monthly NDVI (2000–2017) data across PFS and EFS in all selected catchments were compared and analysed. Three different vegetation greenness patterns were observed: (1) PFS were always greener than EFS; (2) PFS were greener in summer, but EFS were greener in winter; and (3) there were almost negligible differences in vegetation greenness on opposing hillslopes. An overwhelming 70% ...
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