Assessment of trends in rainfall-runoff events in a mountain basin: analysis of the influence of initial conditions by means of a hydrological model and GIS

Despite the expectation that increases in rainfall with climatic change will result in increases in pluvial flooding, there is more historical evidence for decreases in flood magnitude. The small basin of La Vizza, in the Eastern Italian Alps, provides a clear example for this type of trend divergence. In this basin, flood magnitudes are decreasing, despite increasing rainfall extremes. In this thesis we investigate how changes in soil moisture and snow water equivalent play a role in controlling the above divergence. Using catchment average precipitation and temperature, and a continuous hydrological model able to specify soil moisture and snow water equivalent at the start of each rainfall-runoff events, we aim to better understand the relative role of the two drivers in controlling the trends in runoff events (both volumes and peaks). With this overarching objective, the thesis has the following specific objectives: i) Quantify the diverging trends in annual maxima of rainfall and runoff events for the study basin; ii) Quantifying the snow cover area and snow water equivalent by means of the TOPMELT model and validating it by using MODIS satellite images; iii) Quantify the trends for event-generating precipitation, antecedent soil moisture, and antecedent snow water equivalent and assess their role in controlling the trend in runoff events. The monotonic trends will be assessed using the non-parametric Mann-Kendall test and the trend slopes will be determined by Sen’s slope method. The findings of this research will have significant implications for understanding the role of the underlaying hydrological factors such as soil moisture and snow water equivalent controlling the trends in rainfall-runoff events in other similar mountain basin.