Water resource issues in developing countries
A concise presentation of pertinent water resource issues, with particular emphasis on developing countries and Ethiopia, is made. The various water resources issues are grouped into four classes: water quantity issues, water quality issues, hydrological extremes, and soil erosion and reservoir sedimentation.
Water quantity issues
Water is required to meet various consumptive and non-consumptive uses. Consumptive uses comprise water for irrigation, domestic and industrial supplies. Non-consumptive uses include water required for hydropower generation, waste disposal, fish and wildlife habitat, inland transport and recreation. Meeting these needs for water is becoming increasingly difficult worldwide due to rapid population growth, improving living standards, urbanization and expansion of agricultural and industrial activities (Jones, 1997). A comprehensive study on water resources vulnerability indicated that about 60% of the world population would live in moderately to extremely vulnerable regions by year 2025 (Kulshreshtha, 1998). The spatial and temporal variability of water availability together with impacts of land use and climate changes would exacerbate the problem.
Water scarcity is serious in the developing world where most of the population growth takes place and the coping-up capacities are weak. Half of the population of developing countries lives in water poverty, having difficulty of getting a minimum per capita share of 1700 m3/year (WWAP, 2009). In Asia and Africa water is said to be a major constraint for agriculture in the coming decades (Rijsberman, 2006). In Africa, only one-seventh of the continent has surplus runoff, making water shortage a critical problem (Jones, 1997). The transboundary nature of many rivers complicates and politicizes the issue of water supply-demand issues. Large parts of Africa (60%) and Asia (65%) are located within transboundary river basins where, in most cases, binding water use agreements are lacking (Jones, 1997).
The problem could also be an issue of major concern in Ethiopia as the various factors that could lead to water scarcity do exist. An average per capita water share of 1700 m3/year could be obtained based on the recent population census data and total freshwater potential of the country. Water resources vulnerability is found to be high in Ethiopia according to a recent study conducted for Eastern Nile Basin countries (Hamouda et al., 2009). Moreover, the high spatial and temporal variability of water resources in Ethiopia makes the issue more serious. Eighty three percent of the country has drier climate (moisture index ranging from -60 to 0) with limited surplus water during the rainy season (Gonfa, 1996). The lowlands are water deficit regions with unreliable annual rainfall of 200-600 mm. Most of the highlands receive annual rainfall in excess of 1000 mm, but it is highly seasonal with most of it occurring between June and September (Korecha and Barnston, 2006). The highlands are also regions where population concentration, urbanization, and increasing agricultural and industrial activities are seen. The water scarcity problem may also be aggravated by climate change. For instance, predictions of hydrological impacts of climate change indicated decreases in runoff in catchments located in the south central and eastern parts of the country (Hailemariam, 1999; Legesse et al., 2003). The transboundary nature of most rivers of Ethiopia is a serious challenge (World Bank, 2006). It is particularly serious in the Blue Nile Basin which contributes about 60% of the Nile flow. The Nile basin is shared by 10 riparian countries whose major source of livelihood is agricultural production. Equitable water allocation has been and continued to be a serious issue among the basin countries.
The pressure on the freshwater resources of Lake Tana Basin would mount, as the various factors that are responsible for water demand increase do exist. According to the recent census data, a total population of about 7 million lives in and around the basin (CSA, 2008). Two major cities of the country, Bahir Dar and Gonder, with more than 200000 residents each are located within the basin. Moreover, the Lake Tana region has been identified as one of the economic growth corridors of the country (MoFED, 2006). To this end implementation of water resources development projects that are identified in the Abay Basin Master Plan study (BCEOM, 1999a) has been going on. The Tana-Beles multipurpose project that relies on water transfer from Lake Tana was recently completed. Major dam projects for irrigation agriculture are going in different parts of the basin. A simulation study on the impact of the different development scenarios indicated a decrease in the level and area of the lake with anticipated socio-economic and environmental impacts (Alemayehu et al., 2009). Water resources of Lake Tana basin are said to be susceptible to climate change with predicted reduction in streamflows (Hassan, 2006; Abdo et al., 2009).
Water quality issues
Freshwater quality impairment has been a major issue of concern worldwide. The sources of water pollution can be point or diffuse sources. Point sources of pollution include municipal and industrial wastewaters for which specific points of entry to a receiving water body can be identified. Diffuse sources of pollution include general land runoff from urban and agricultural areas and other sources that do not have specific discharge points. Unlike point sources, diffuse sources of pollution are difficult to manage (Novotony and Olem, 1994). Due to the extensive damages that could be caused by diffuse sources of water pollution, the need for addressing the issue as an international priority of concern was already heralded long ago (Duda, 1996). Diffuse pollution is considered to be the dominant cause of water quality impairment in many developing countries due to poor waste management and environmentally unfriendly agricultural methods (Novotony, 1995). For instance, a study in Uganda indicated pollution from diffuse sources to be higher than point sources (Banadda et al., 2009). Water quality impairment in general, and diffuse pollution in particular, can be a serious problem in Ethiopia for reasons related to widespread sources of pollution, favoring hydrologic factors and lack of environmental services. The favorable hydro-meteorological factors are related to the nature of the rainfall climate and watershed characteristics. Many catchments in Ethiopia receive intense seasonal rainfall on steep slopes that have scarce vegetation cover. These factors enhance high surface runoff and transport of sediments and associated contaminants. Though a general and systematic water quality assessment program is lacking, isolated studies indicated existence of water pollution problems (MoWR et al., 2004). Major urban centers and industrial establishments are sources of water pollution due to inadequate waste management services. For instance, pollution of streams that drain Addis Ababa due to poor waste management practices is considered to be a major problem with adverse public health and ecological impacts (Nigussie, 1999; Gebre and Rooijen, 2009). Various Water quality studies on rift valley lakes indicated problems of pollution that include eutrophication, heavy metals, salinity, and other pollutants (Zinabu et al.,2002, 2003; Teklemariam and Wenclawiak, 2005; Ayenew, 2007). The causes of these problems are related mainly to improper utilization of land and water resources in the lakes catchment (Legesse and Tenalem, 2006). In another study high salinity level is noted in the middle Awash River Basin due to intensive irrigation and upstream pollution sources (Tadesse et al., 2007).
Water quality studies in the Lake Tana Basin are limited. But, considering the extensive agricultural activities using chemical fertilizers, the growing urban settlement with poor waste management services, as well as the favorable hydrological factors of erosion, the problem of water pollution could be high. Indications of pollution of Lake Tana, with adverse socio-economic and ecological impacts have already been reported (Teshale et al., 2001). Assessment of the impact of Bahir Dar city on pollution of Lake Tana and groundwater resources indicated high levels of nutrient and suspended sediment loads (Wondie, 2009).
Two common and devastating hydrological extremes, floods and droughts, are discussed. These disasters continue to affect generations, bringing suffering, death, and immense material losses worldwide.
A flood is an unusual high-water period in which water overflows its natural or artificial banks onto normally dry land. Flood can cause great damage to land and water-related infrastructure and it can have disastrous short and long-term consequences on people and economies. Flooding problem is a critical issue in developing nations due to the magnitude of the problem and lack of adequate coping-up mechanisms. A storm surge flood in 1991, for instance killed 140 000 persons in Bangladesh (Kundzewicz and Kaczmarek, 2000). In Africa, Mozambique was hit by a devastating flood that caused huge socio-economic disruptions (Christie and Hanlon, 2001). Since the mid 1990s Africa has become the second most flood-affected continent in the world following Asia (Yoganath and Junichi, 2009).
In Ethiopia flooding affects mainly riverine and lowland areas with adverse consequences on agricultural land, settlements and infrastructure. Areas commonly flooded in Ethiopia include the Gambela Plain in the Baro-Akobo Basin, floodplains and irrigation areas along the Awash River, the lower parts of Wabi-Shebele Basin and the downstream reaches of major catchments in Lake Tana Basin (Woube, 1999; Achamyeleh, 2003). The socio-economic impacts of flooding could be huge as exemplified by the year 2006 incident which covered almost the entire country with affected population of about 700 000 (EWD, 2007).
Flooding is a recurrent problem in the Lake Tana basin (SMEC, 2008a). Flood risk areas include floodplains located in the downstream reaches of Megech, Rib, Gumara and Gilgel Abay rivers. Flooding is caused by combination of factors that include bank overflow, sedimentation, poor drainage, lake level rise, and changes in the watershed characteristics. The impacts of past flood incidents were serious with displacements of several inhabitants and inundation of croplands (Riverside et al., 2009).
In the literature different types of drought are recognized- meteorological, hydrological, agricultural and socio-economic drought (Kundzewicz et al., 2002). Meteorological drought is generally taken as shortage of rainfall. A meteorological drought can develop into agricultural drought which is described by soil moisture deficit and low crop productivity. Hydrological droughts are characterized by a reduction in lake storage, lowering of groundwater levels and decrease of streamflow discharge. A socio-economic drought occurs when the demand for water and water-related economic goods and services (e.g., fish, hydropower, irrigated agriculture and horticulture) exceed supply. Hydrological droughts usually lag the occurrence of meteorological and agricultural droughts. Although climate is a primary contributor to hydrological drought, other factors such as changes in land use (e.g., deforestation), land degradation, and construction of dams all can affect the hydrological characteristics of a basin. Because regions are interconnected by hydrologic systems, the impact of hydrological drought may extend well beyond the borders of precipitation-deficient area.
Drought is an issue of great concern in several countries, particularly, in the developing world. The African continent suffered an extraordinary drought without precedence in the records due to a significant drop in precipitation and decreasing streamflows (Kundzewicz and Kaczmarek, 2000). Global analysis of water related disasters between 1980 and 2006 indicated that 99% of the total drought fatalities were in Africa (Yoganath et Junichi, 2009). In sub-Saharan Africa, where rain-fed agriculture is the predominant economic sector, drought poses a great challenge to the overall performance of their economies (Gautam, 2006).
Drought is a recurring phenomenon in Ethiopia, with increased frequency of occurrence in recent years (MoWR et al., 2004). According to the international disaster database, drought has been top in the list of natural disasters affecting millions in the country for long (CRED, 2010). Combinations of the various types of drought could be the cause of the problem (MoWR et al., 2004). Drought analysis in the Awash River indicated an average lag period of 7 months between hydrological and meteorological droughts (Edossa and Babel, 2010). The adverse socio-economic impacts of drought are huge as most of the population depends on agriculture and hydropower is the major source of electricity. For instance during the 1984/85 drought GDP declined by 9.7 percent, agricultural output declined by 21 percent, and gross domestic savings declined by 58.6 percent (World Bank, 2006). Lower water level in reservoirs has also been a major cause for extensive power rationing in recent years.
Soil erosion and reservoir sedimentation
Soil erosion by water and subsequent sediment transfer are global issues of great concern because of their multiple adverse onsite and offsite consequences. The onsite effects include soil degradation and reduction in crop productivity which would lead to food insecurity (Lal, 2001; Blanco and Lal, 2008). The offsite consequences are diverse and include changes in channel morphology and habitat, reservoir sedimentation, transport of sediment-adsorbed nutrients and contaminants such as particulate phosphorus, heavy metals, and pesticides (Owens, 2005; Owens and Collins, 2006). Because of its diverse negative effects, soil erosion is considered to be the single most environmental degradation problem in developing countries (Ananda and Herath, 2003). Soil erosion contributes to chronic malnutrition and rural poverty in these countries because of farmers’ weak capacity to establish mitigation measures (Blanco and Lal, 2008).
Sedimentation in reservoirs and river beds could be an issue of major concern due to its multiple effects. Some of the adverse effects include loss of storage capacity, damage of hydraulic structures, modification of river morphology, and disruption of aquatic habitat (Morris, 1998). Reservoir sedimentation is considered to be one of the most economically crippling problems because of large investments in dams for generation of hydroelectric power and irrigation development (Nagle et al., 1999). For example, a drastic reduction in hydropower generation and inefficiency of irrigation schemes due to large sediment loads coming from Ethiopian highlands are noted to be serious problems encountered at Roseires Dam in Sudan (Elsheikh et al ., 1991). Siltation in Lake Victoria is one of the critical factors that is affecting the fishing industry (Ntiba et al., 2001).
Soil erosion by water has been a longstanding environmental problem in Ethiopia and is considered to be a critical economic problem (Hurni, 1993; Bewket and Sterk, 2003). The annual rate of soil loss in the country is greater than the annual rate of soil formation (Tamene and Vlek, 2008). The rate of soil erosion is high due to a number of favoring factors that include erosive rains, steep gradients, cultivation on steep terrain, deforestation, overgrazing, and poor agricultural techniques (REDECO and HSD, 2002; Nyssen et al., 2004). The most important soil erosion processes are sheet and rill erosion, and water-induced soil movements by gullying and landsliding, particularly in the highlands (Oldeman et al., 1991; Nyssen et al., 2004). The mean annual soil loss rate by sheet and rill erosion in the highlands is estimated to be 12 t/ha (Hurni, 1990). The soil loss rate from croplands by sheet and rill erosion is 42 t ha-1 year-1. Assessment of gully erosion rates is limited in which soil loss rates of 26 t ha-1year-1 and 6.2 t ha-1 year-1 are noted, respectively, in the eastern and northern highlands (Shibru et al., 2003; Nyssen et al., 2006).
Different studies indicated siltation of water systems in different parts of the country as a major problem in Ethiopia. Assessment of siltation of water harvesting schemes in the northern highlands indicated that most of them will be filled with sediment within less than 50% of their intended service time (Tamene et al ., 2006). Land degradation due to soil erosion and reduction of storage capacity of Lake Alemaya, in the eastern highlands of Ethiopia, is dubbed as a serious problem (Muleta et al., 2006). Siltation and nutrient enrichment are found to be the major problems of Gilgel Gibe hydropower dam which is located in the southwestern part of the country (Devi et al., 2008).
Soil erosion and sedimentation could be a major threat in the Lake Tana basin. Agriculture is the mainstay of most of the population in the basin and hence land degradation by soil erosion would directly affect the lives of millions. Sedimentation could adversely affect the storage capacity, socioeconomic values and ecological health of Lake Tana. Moreover, the capacity and efficiency of the existing and ongoing dam projects in the basin could be endangered. Factors that contribute to accelerated soil erosion are evident in the basin and include extensive cultivation (even on steep slopes), overgrazing, scarce vegetation cover on hillslopes, and high rainfall intensity. Some relevant studies indicated high rates of soil erosion and adverse impacts of siltation. A recent study by Tebebu et al. (2009) on hydrological controls of gully formation in the southern part of the basin indicated an average gully erosion rate of 24.8 t ha-1 year-1. A modeling study found 18.4% of the basin highly susceptible to erosion with estimated sediment yield of 30 t ha-1 year-1 (Setegn et al., 2009). Siltation in the downstream reaches of the major rivers is one of the causes of overbank flow and flooding (SMEC, 2008a).
Concluding remarks on water resources issues
The notes made in the previous sections did indicate how diverse and critical are watershed problems in the developing world and the study area. The analysis and management of the issues is even more challenging for various reasons. Some of the key constraints include weak institutional arrangements and inadequate human, financial and technical capacities. Lack of adequate and reliable hydro-meteorological and spatial data is the other major scientific challenge that contributes to the improper formulation of problems and evaluation of management options. Many catchments are ungauged or poorly gauged in many parts of the world and the problem is worse in developing countries (Sivapalan, 2003). In Ethiopia in general, and the study region in particular, there are several ungauged or poorly gauged watersheds. Examples of specific problems associated with data availability include lack of hydro-meteorological data at shorter time scales, representation of the naturally heterogeneous land surface elements such as soil and vegetation types by very coarse-resolution. Such problems make applications of hydrological models difficult, resulting in high prediction uncertainties. As a response to this critical issue, the International Association of Hydrological Sciences (IAHS) launched an international initiative called Predictions in Ungauged Basins (PUB) and declared the period 2003-2012 as the decade of PUB (Sivapalan et al., 2003). So far diverse promising outputs of the initiative have been noted (e.g. Sivapalan et al., 2006). Different strategies can be used to bridge data paucity and make hydrological predictions possible. Some of the strategies may include use of data from diverse sources, disaggregation of existing meteorological data to finer time scales, application of pedotransfer functions to derive soil hydraulic properties, and estimation of values of model parameters from watershed physical characteristics through regionalization techniques. Such strategies have been used in this study to make it more scientific.
Table of contents :
1 Water Resources Issues
1.1 Water resource issues in developing countries
1.1.1 Water quantity issues
1.1.2 Water quality issues
1.1.3 Hydrological extremes
1.1.4 Soil erosion and reservoir sedimentation
1.1.5 Concluding remarks on water resources issues
1.2 Role of hydrology, and erosion and sediment transfer in watershed management
1.3 Hydrological modeling
2 Description of the Study Area
2.3 Geology and soil
2.4 Land use and land cover
2.6 Hydrology and hydrogeology
2.7 Water resources development
3 Data availability and analysis
3.1 Meteorological data availability
3.1.2 Wind speed, relative humidity and sunshine hour
3.2 Hydrological data availability
3.2.1 Streamflow and lake level
3.2.2 Suspended sediment
3.2.3 Lake Tana bathymetry
3.3 Spatial data availability
3.3.1 Soil types and properties
3.3.3 Digital elevation model
3.4 Data analysis
3.4.1 Analysis of meteorological data
3.4.2 Hydrological data analysis
3.4.3 Suspended sediment yield
3.4.4 Soil and land cover data analysis
3.5 Concluding remarks
4 Sensitivity analysis of Distributed Hydrology, Soil, Vegetation Model Parameters
4.2 Materials and methods
4.2.1 Description of the model
4.2.2 The sensitivity analysis method
4.2.3 Virtual catchments
4.3 Results and discussion
4.3.1 Sensitivity to terrain slope
4.3.2 Sensitivity to soil depth
4.3.3 Sensitivity to soil parameters
4.3.4 Sensitivity to vegetation parameters
5 DHSVM Input Data Creation for Lake Tana Basin
5.2 Weather data disaggregation
5.2.3 Wind speed
5.2.4 Relative humidity
5.2.5 Solar radiation
5.2.6 Downward longwave radiation
5.3 Spatialization of meteorological data
5.4 Creation of spatial datasets
5.4.1 Soil and land cover maps
5.4.2 Soil depth
5.4.3 Binary maps
5.4.4 Stream files
5.5 Creation of initial model state files
5.6 Parameterization of soil and vegetation properties
5.7 Creation of configuration file
5.8 Concluding remarks
6 Application of DHSVM to Selected Catchments in the Lake Tana Basin
6.2 Calibration and validation of models: Literature review
6.2.3 Model performance measures
6.3 Selected catchments
6.4 Calibration and validation of the model
6.5 Results and discussion
6.5.1 Performance of the model at daily time step
6.5.2 Performance of the model at monthly time step
7 Water and Suspended Sediment Balances of Lake Tana
7.2 Lake water balance model
7.3 Computation of the water balance components of Lake Tana
7.3.2 Inflow from contributing catchments
7.3.4 Interaction with groundwater
7.3.5 River outflow
7.3.6 Floodplain evaporation
7.3.7 Change in lake water storage
7.3.8 Summary of the major water balance components of Lake Tana
7.3.9 Simulation of lake level fluctuation
7.4 Suspended sediment balance of Lake Tana
7.4.1 Suspended sediment discharge from gauged catchments
7.4.2 Suspended sediment discharge from streams with no data
7.4.3 Total suspended sediment inflow
7.4.4 Suspended sediment outflow
7.4.5 Suspended sediment deposition
7.5 Concluding remark
General conclusion and perspectives
Summary and conclusion
Uncertainty and sensitivity analysis
Meteorological data disaggregation
Testing DHSVM on other catchments
Further study on suspended sediment