## 5 Discussion  
### The Potential, Uncertainties and Limitations of LULCC Analysis and SWAT Application  
Land use classification is based on transferring continuous spectral signals into discrete classes [46]. This generates errors that must be reported in order to evaluate the validity of the maps or the models using the LULC data. In our case, water, wetlands and arable land were rather homogeneous classes. However, the forest class was spatially often very heterogeneous, with areas of open forests mixed with patches of grasslands or arable land. This caused the estimations of forested areas to be less accurate, especially for the 1990 map due to lack of quality training and validation data. Considering these limitations, the high rates of agricultural expansion at the expense of wetlands first are still very obvious, especially during the period 2004-2016. At the catchment scale the impact of the changes for the period 1994-2014 seem to be negligible at first glance concerning the flow duration curve (Figure 5). However, the flow duration curve displays the ranked discharge values of 15 simulation years for each land use scenario. Hence there is no temporal information when discharge thresholds are exceeded and only the percentage of data exceeding certain thresholds is shown. Nevertheless, a shift from the 1970s scenario to the more recent land use scenarios (1994 to 2014) can be observed. The simulated changes in land use patterns from the 1970s compared to other scenarios result in decreasing low flows and increasing high flows as shown in Figure 5. These changes in low flows  
Figure 6: Percentage shifts in water balance components (Table 4) for the whole catchment and investigation period (1958–1970) through the application of different land use maps. and high flows affected the overall hydrological regime of the Kilombero river. On the one hand, increasing high flow events had an impact on the inundation height and duration during the rainy season and on the other hand, decreasing low flows were directly linked to the surface groundwater interaction in the floodplain during the dry season, altering the depth to groundwater table dynamics and hence the overall soil water availability. On a seasonal scale this shift probably influenced already implemented and planned cropping schemes, especially with respect to the planned intensified agricultural cultivation [31]. This potential impact on agricultural management was emphasized when analyzing single components of the water balance. In addition to the above mentioned changes from the 1970s scenario it was apparent that shifts in the water balance can be observed among the scenarios from 1994 to 2014 (Figure 6). This is especially true of the increase in surface runoff and the decrease in baseflow which was caused by the conversion from open woodland into cropland/grassland [88] resulting in an overall increase of high flow events and a decrease of low flow events respectively (Figure 5). Furthermore, the high evapotranspiration rate of the 1970s scenario was related to the overestimation of the land use class open water in the floodplain area (Figure 4) because available Landsat images were exclusively from the wet season. However, the conversion of open woodland to cropland and grassland decreased actual evapotranspiration rates. This was mainly observed in the land use change scenario from 1994 to 2004 (Figure 6) with a major shift from open woodland to grassland (Tables 6 and 7). In general, this analysis indicates that the observed changes led to decreased actual evapotranspiration and baseflow whereas surface runoff increased, altering the hydrological regime of the Kilombero river. However, the simulated components of the water balance (Figures 5 and 6) were aggregated by areal means over the entire simulation period. Future research should focus on smaller timescales such as seasonal changes as well as more detailed spatial analyses.