CHAPTER 2 LITERATURE REVIEW
2.2 Discussion
24 which can be derived directly from catchment data. Hence relevant information can be generated for water management in data scarce catchments although they do not have enough data.
Figure 2.3: Representation of hydrological processes in the ACRU model (Schulze, 1995)
25 area in Benin, have used realistic land use scenarios, where simulated land use change was influenced by socio-economic and biophysical driving forces.
Moreover, although the use of the scenario approach to climate change impact analysis generates valuable information for sustainable water resources management, studies in West Africa have generated varied results depending on the scale of analysis, the season and the hydrological model applied. The results of the reviewed studies show that the hydrological cycle in West Africa will undergo severe changes, if the applied climate change scenarios come true. Nevertheless, the uncertainties with climate change scenarios and to some extent the downscaling methods, were the most important factors affecting the simulation accuracies, which is also confirmed in studies elsewhere in the world (Dibike and Coulibaly, 2005;
Buytaert et al., 2010; Kingston and Taylor, 2010; Tshimanga and Hughes, 2012). IPCC (2007) reports indicate that different GCMs project different climates, especially rainfall for West Africa. Hence, the over-reliance on single climate scenarios, as well as single GCMs, for climate impact analysis in West Africa, has also resulted in large uncertainties in predicted hydrological impacts. It has been suggested that downscaled ensemble climate scenarios, are required in order to reduce climate impact simulation uncertainties at the regional/local scales (Buytaert et al., 2010; Quintana Segui et al., 2010; Taye et al., 2011). In West Africa, the opportunity to assess the range of uncertainties of predicted impacts of climate change on hydrology will be improved with ensemble simulations, which will pave the way for probabilistic planning of water resources (Fowler et al., 2007).
In addition, case studies elsewhere in the world (Li et al., 2009; Park et al., 2011; Tong et al., 2012), illustrate that it is not enough to conduct separate assessment of land use change and climate change impacts on hydrology to provide information for effective land use planning and water resources management. It is essential to quantify the combined impacts across scales, using appropriate methods and tools. This is because land use and climate affect each other (Dale, 1997; IPCC, 2007; D'Orgeval and Polcher, 2008) and their separate and simultaneous impacts are non-linear. Unfortunately, in West Africa, where climate change and land use change are affecting all aspects of life (Jalloh et al., 2013), studies focusing on the combined impacts of climate change and land use changes on hydrology are rare (Seguis et al., 2004; Bormann, 2005; Paturel et al., 2007; Bossa et al., 2012; Cornelissen et al., 2013;
26 Bossa et al., 2014) and none of them assessed the potential alteration in ecology due to impacts of global changes on hydrology.
Finally, almost all the climate change impacts studies (Paturel et al., 2007; Ardoin-Bardin et al., 2009; Bossa et al., 2012; Ruelland et al., 2012; Cornelissen et al., 2013; Sood et al., 2013) in West Africa analysed short-term impacts, based on single GCMs, regional scales and focused on the Savannah/semi-arid regions. Studies on either separate or joint impacts of global changes in West Africa have also used mainly conceptual hydrological models, which lack the ability to describe the spatial variability of hydrological processes across scales.
Previous studies in West Africa have also neglected the full range of streamflow responses to land use changes and climate changes, by focusing more on mean streamflows, which does not consider extreme hydrological conditions. To our knowledge, there is no comprehensive and quantitative information on the impacts of global change on hydrology and ecology in the tropical rainforest regions of West Africa, where majority of the population live and where land use changes may exacerbate impacts of climate change on water resources, due to rapid population changes. The most likely reason for this state of affairs is that of data scarcity and limited capacity in West Africa, which makes the region vulnerable to the consequences of climate changes and land use changes. Adaptation strategies in the region can therefore benefit from improved understanding of the regions hydrology by resolving key issues in data scarcity (e.g. improve meteorological network and use of remote sensing for mapping land use and realistically simulating future land use) and building institutional capacities to make reliable predictions on global change impacts, across scales.
2.2.2 Hydrological Model Selection
Fully-distributed models are the best for assessing spatial patterns of land use and climate change impacts on streamflows, but are data intensive. The use of semi-distributed models such as the ACRU is important for data scarce catchments since the models although require less data, compared to fully distributed models, they are able to represent some of the spatial patterns in streamflows, required for effective water resources management at the local scale.
The ACRU model for example is useful for data scarce regions because it is relatively less
27 data intensive and its flexible approach to simulation allows users to input information based on reading of the landscape. The model is also sensitive to changes in land use and climate and has been applied successfully in a variety of catchments with diverse land use and climates. The ACRU model can therefore be useful for streamflow simulation in the rainforest catchments of West Africa, as these catchments are undergoing significant land use changes.