Development and application of a GIS-based regional hydrological variability and impact assessment system (RHVIAS) for Southern Africa Region

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University of Dar es Salaam
Local or regional water resources planning and management is a complex problem. Clearly, hydrologic aspects constitute the major component. In addition, hydrological assessment of the existing and the future water-resources availability of a region is an important aspect. Assessing the environmental impact of the indisputable possible global climate change on regional water resources is another fundamental global concern. This calls for the development of a distributed hydrological model that accounts for the spatial variation and regional distribution of the various natural resources and environmental assets of a region. For this purpose, a GIS-based regional hydrological variability and environmental impact assessment system (RHVIAS) is developed. The system links the different components for analysis of regional water resources availability, variability and environmental impact assessment (EIA) of possible climate change on water resources at a regional scale. The system developed in this work has three components: variability analysis subsystem (VAS), a hydrological modeling subsystem (HMS), and an environmental impact assessment subsystem (EAS). The Southern African subcontinent, the SADC region, is considered for this study. The variability analysis subsystem (VAS) is composed of a system of time series models for hydrological variability analysis. It constitutes sub-modules for: (i) studying the annual and seasonal river runoff variability of 665 rivers, (ii) detection of possible climate change using a century-record of annual precipitation and temperature, and (iii) attribution study of climate change in terms of El Nino effects on river runoff variability using correlation analysis. VAS is externally coupled with ArcView~GIS for portraying the spatial coherence of identified temporal variability in the river runoff regimes. The hydrological modeling subsystem (HMS) is a system comprising a distributed GISbased hydrologic model (DGHM). It considers the geo-referenced distributed ground and satellite-based information such as soil, vegetation and other hydro-climatic information. DGHM simulates regional water balances such as runoff, soil moisture acid evapotranspiration for any grid, using GIS based temporal information and coupling with stochastic weather generation models (WGMs) for weather disaggregation. The WGM for rainfall has been built from a network of 760 rain gauge stations consisting of daily rainfall of length 2-91 years recorded in this century throughout the Southern African region. Both descriptive ability and predictive ability statistical tests have revealed the potential applicability of the model to generate rainfall at any selected grid in the region. The environmental impact assessment subsystem (EAS) constitutes a module for EIA of climate change on the water resources. It uses DGHM and it is externally coupled with a set of global climate models (GCMs) and simulated regional climate change scenarios. A coupling procedure is formulated to make a link in EAS between the GCM derived climates and DGHM through WGMs. Three GCMs are coupled in EAS selected from a suite of 14 GCMs tested - based on the IPCC 1992 emissions scenario (IS92a) and associated global warming with respect to the baseline 1961-90 climatology of the region. The selected GCMs represent relatively wet, dry and moderate scenarios, and they are the Oregon State University (OSU) model, the Hadley Centre 1994/95 model (HADCM2), UK Hadley Centre 1992 model (UKTR). Each component of RHVIAS, viz. VAS, HMS and EAS, has been tested individually, and finally integrated as interactive user-interface package to undertake an integrated water resources assessment. The approach used in VAS provided an excellent environment for undertaking variability analysis in temporal horizons and portraying attributes in a spatial context using GIS tools, for 665 gauged catehments in Southern Africa. River runoff declines since mid of 1970s have been prevalent in central and southern part of the SADC region. In the 20th century, temperature rises at a rate of 0.09° C per decade, and rainfall variation of mainly ±20% have been investigated. A correlation analysis of seasonal El-Nino/Southern Oscillation (ENSO) indices (that occurred since mid of 1950s to 1998) and annual discharge of selected rivers in the region is carried out. It reveals that a significant variance is accounted for by the ENSO episodes that suggest possible El Nino contribution to the natural variability of runoff. The HMS provides an excellent tool for simulating regional water balances at georeferenced grids of 0.5° resolution covering the region. It simulates the 1961-90 monthly runoff, evapotranspiration and soil moisture regimes of the SADC region. EAS provides a means of portraying regional water resources availability for the current and post-climate change conditions as a result of the simulated set of regional climate change scenarios predicted by GCMs. The 1961-90 average mean annual runoff from the land catchments in Southern Africa, generated using the developed model, in the region is about 151 mm per year, although there is a significant inter-regional variation among the SADC countries. Surface water availability in the region will be less reliable, and runoff changes are expected to be within ±20% in the 2050s; however, decision-makers should,be aware of the sub-regional variations and uncertainties associated with GCM-based climate change projections in formulating strategies to cope with the risks of climate change. Integrated water management at the river basin level remains the key action to alleviate water scarcity in the region. Potential actions to mitigate fossil fuel emissions such as increased agro-forestry and energy conservation & efficiency, employment of renewable energy systems and use of alternative fuels are suggested. Measures taken to reduce GHGs simultaneously reduce local and regional pollution. Designing the right response, in the region or a particular country, however, presents a tough challenge; while benefits accrue to the whole world, the costs accrue to the country where the investment or policy change takes place. The author has explored the implication of global efforts in abating or mitigating climate change - from the formation GEF to the Kyoto Protocol - and the provision of the UNFCCC framework for countries to address the treat of climate change.
Available in print form
Water analysis, Southern Africa
Berhanu, F. A. (1999) Development and application of a GIS-based regional hydrological variability and impact assessment system (RHVIAS) for Southern Africa Region, Masters’ dissertation, University of Dar es Salaam. Available at (