Water Supply Regimes Research Articles

The optimization of predicting the liquefy of pulp in a ball mill at variable flow of water in sand of the classifier

To diminish the cost of iron-ore concentrate is possible by stabilization in the ball mill ratio ore / water, and this work is devoted to find it. In this work we used an algorithmic approach of the determination of the controlled value, the dynamic programming method and the Gauss-Seidel’s method, method of analytical calculations with using the mathematical model of the process, the theory of accuracy, the theory of signal filtering, the theory of sensitivity of optimum, modeling of the processes in the sand trough of the single-spiral classifier during valuing the water supply regimes in the sands. Prediction of ore / water ratio at a constant flow of the water in the sand of the classifier optimization of the selection information means by accuracy is made at the level of permissible error of ± 3,0 % with a significant reserve (of error) in a conditions of high error of measurement of pulp, it improves the indices of the ball mill, but has identified detects. Much better results provides regimen of stabilization pulp liquefaction in the sand trough. Prediction the index in these conditions could provide at level of error ± 3,0 % in case of increasing the accuracy of the conveyor balance. The work demonstrates for the first time the possibility of creating devices of ratio ore / water prediction in a ball mill in the stabilization of pulp liquefaction in the sand trough by implementation of the algorithmic approach and optimize the choice of measuring devices by accuracy. The practical significance consists in the increasing of production of the ball mill and economy electricity, steel balls and inwall.

Dominance of an alien shrub Rhus typhina over a native shrub Vitex negundo var. heterophylla under variable water supply patterns.

Temporal heterogeneity of a resource supply can have a profound effect on the interactions between alien and native plant species and their potential invasiveness. Precipitation patterns may be variable and result in a higher heterogeneity of water supply with global climate change. In this study, an alien shrub species, Rhus typhina, introduced to China from North America and a native shrub species, Vitex negundo var. heterophylla, were grown in monoculture and mixed culture under different water supply regimes, with four levels of water supply frequencies but with a constant level of total supplied water. After 60 days of treatments, the alien species was found to be the superior competitor in the mixed culture and was unaffected by changes in the water supply pattern. The dominance of R. typhina was mainly owing to its greater biomass and effective modulation of leaf physiology. However, in the mixed culture, V. negundo var. heterophylla exhibited both leaf- and whole-plant-level acclimations, including higher leaf length to petiole length and root to shoot biomass ratios, and lower specific leaf weight and leaf length to leaf width ratio. Plant height of V. negundo var. heterophylla was comparable to that of R. typhina in the mixed culture, which is a strategy to escape shading. Although water treatments had little effect on most traits in both species, the possible influence of water regimes should not be neglected. Compared with high-frequency water supply treatments, more individuals of V. negundo var. heterophylla died in low-water-frequency treatments when in competition with R. typhina, which may lead to species turnover in the field. The authors recommended that caution should be exercised when introducing R. typhina to non-native areas in the context of global climate change.

Measuring household consumption and waste in unmetered, intermittent piped water systems

AbstractMeasurements of household water consumption are extremely difficult in intermittent water supply (IWS) regimes in low‐ and middle‐income countries, where water is delivered for short durations, taps are shared, metering is limited, and household storage infrastructure varies widely. Nonetheless, consumption estimates are necessary for utilities to improve water delivery. We estimated household water use in Hubli‐Dharwad, India, with a mixed‐methods approach combining (limited) metered data, storage container inventories, and structured observations. We developed a typology of household water access according to infrastructure conditions based on the presence of an overhead storage tank and a shared tap. For households with overhead tanks, container measurements and metered data produced statistically similar consumption volumes; for households without overhead tanks, stored volumes underestimated consumption because of significant water use directly from the tap during delivery periods. Households that shared taps consumed much less water than those that did not. We used our water use calculations to estimate waste at the household level and in the distribution system. Very few households used 135 L/person/d, the Government of India design standard for urban systems. Most wasted little water even when unmetered, however, unaccounted‐for water in the neighborhood distribution systems was around 50%. Thus, conservation efforts should target loss reduction in the network rather than at households.

Apple Tree Responses to Deficit Irrigation Combined with Periodic Applications of Particle Film or Abscisic Acid

The objective of this study was to determine if the application of two antitranspirant compounds would moderate water deficit stress effects on physiological responses of “Granny Smith”, “Royal Gala” and “Golden Delicious” apple (Malus domestica Borkh.) trees on MM106 rootstock that occur during deficit irrigation. Uniform trees were grown in pots under water supply regimes of 30%, 60%, and 80% depletion of available water (DAW) before irrigation to runoff and received applications of kaolin particle film (PF) or abscisic acid (ABA) at 0, 30 and 60 days. At 120 days, genotype and deficit irrigation affected nearly all leaf traits, but antitranspirant treatment had no significant effects. As the % DAW increased, the net photosynthetic rate (Pn), transpiration rate (T), stomatal conductance, leaf water and pressure potential, variable-to-maximal chlorophyll fluorescence, leaf number, and leaf N, P and K contents were reduced. A significant genotype by deficit irrigation interaction was evident on T, water use efficiency (WUE), and leaf osmotic pressure potential. A significant deficit irrigation by antitranspirant interaction was evident on only leaf Pn, with PF and ABA reducing it at 30% DAW and only PF reducing it at 80% DAW. However, the periodic use of PF or ABA during deficit irrigation did not alleviate most physiological effects of water deficit stress due to deficit irrigation.

Evaluation of groundwater quality in rural-areas of northern Malawi: Case of Zombwe Extension Planning Area in Mzimba

Many people in in the Sub-Saharan region rely on groundwater for drinking and other household uses. Despite this significance, information on the chemical composition of the water in the boreholes and emperical data on groundwater quality is limited in some rural areas of Malawi. This study was conducted to evaluate the physico-chemical quality of water from boreholes (n = 20) in Zombwe Extension Planning Area (EPA), Mzimba in Northern Malawi to ascertain their safety. Desktop studies and participatory approaches were employed to assess the socio–economic activities and water supply regime in the study areas. The water samples were analysed for pH, conductivity (EC), turbidity, water temperature, nitrate (NO3−), magnesium (Mg), calcium (Ca), zinc (Zn), fluoride (F−), and sulphate (SO42−). In-situ and laboratory analyses were carried out using portable meters and standard procedures. The results were compared with national (Malawi Bureau of Standards – MBS) and international standards (World Health Organization – WHO) for drinking water. The following ranges were obtained: pH (6.00–7.80), EC (437–3128 μS/cm), turbidity (0.10–5.80 NTU), water temperature (27.0–30.60 °C), NO3− (0.30–30.00 mg/L), F− (0.10–8.10 mg/L), Mg (31.00–91.00 mg/L), Ca (20.00–197.10 mg/L), SO42− (10.20–190 mg/L), Fe (0.10–3.60 mg/L) and Zn (0.00–5.10 mg/L). Generally, some parameters tested at several sites (>80%, n = 20) complied with both MBS and WHO limits. No significant differences (p > 0.05) was observed for most parameters (>65%, n = 11). Groundwater contamination was not significant in the area despite some parameters like F−, Ca and SO42− showing higher levels at other sites. Some sites registered very hard water (244.60–757.80 mg/L CaCO3) probably due to mineralization influenced by underground rock material. Further studies are needed to ascertain the groundwater quality of other parameters (like F−, and SO42−) which registered higher levels at some sites. Routine monitoring of the groundwater in the study area and entire Malawi is needed for spatio-temporal variation assessment and to ensure good public health.

Potassium fertilization increases water-use efficiency for stem biomass production without affecting intrinsic water-use efficiency in Eucalyptus grandis plantations

Adaptive strategies to improve tree water-use efficiency (WUE) are required to meet the global demand for wood in a future drier climate. A large-scale throughfall exclusion experiment was set up in Brazil to study the interaction between water status and potassium (K) or sodium (Na) availability on the ecophysiology of Eucalyptus grandis trees. This experiment focused primarily on the changes in aboveground net primary production, stand water use, phloem sap and leaf δ13C, net CO2 assimilation and stomatal conductance. The correlations between these response variables were determined to gain insight into the factors controlling water-use efficiency in tropical eucalypt plantations. The intrinsic WUE in individual leaves (the ratio of net CO2 assimilation to stomatal conductance) was estimated at a very short time scale from the leaf gas exchange. Sap flow measurements were carried out to assess the WUE for stemwood production (the ratio of wood biomass increment to stand water use).Averaged over the two water supply regimes, the stemwood biomass 3years after planting was 173% higher in trees fertilized with K and 79% higher in trees fertilized with Na than in trees with no K and Na addition. Excluding 37% of the throughfall reduced stemwood production only for trees fertilized with K. Total canopy transpiration between 1 and 3years after planting increased from about 750 to 1300mmy−1 in response to K fertilization with a low influence of the water supply regime. K fertilization increased WUE for stemwood production by approx. 60% with or without throughfall exclusion. There was a strong positive correlation between phloem sap δ13C and short-term leaf-level intrinsic WUE. Whatever the water and nutrient supply regime, the gas exchange WUE estimates were not correlated with WUE for stemwood production. Phloem sap δ13C and leaf δ13C were therefore not valuable proxies of WUE for stemwood production. The allocation pattern in response to nutrient and water supply appeared to be a major driver of WUE for stemwood production. In areas with very deep tropical soils and annual rainfall <1500mm, our results suggest that breeding programs selecting the eucalypt clones with the highest growth rates tend to select the genotypes with the highest water-use efficiency for wood production.

Maize root development and grain production as affected by soil and water management on a sandy soil in a semi-arid region of southern Mozambique

ABSTRACTAverage yield of maize (Zea mays L.) in Mozambique is low, mainly due to low use of inputs in agriculture, high seasonal rainfall variability and inadequate soil preparation. A study conducted in two summer crop seasons (November–March 2012/2013 and 2013/2014) examined the impact of three tillage methods (hand hoeing, strip tillage and conventional tillage), two fertiliser levels (0 and 40% N) and two water supply regimes (rainfed and irrigated) on maize root development and grain yield on a sandy soil in a semi-arid region of Mozambique. Tillage had a major effect on soil penetration resistance, but little effect on root growth and limited effect on yield. Thus, there appears to be little need for loosening on this soil. There was also no interaction between tillage and the other experimental factors, meaning that tillage system can be chosen irrespective of fertiliser and water supply. Irrigation had the largest impact on root and shoot growth and crop yield, increasing yield in season 2 from 670 to 4780 kg ha–1.There was a very strong interaction between fertiliser and water supply, with no yield increase for fertiliser in the rainfed treatment, while combined with irrigation it increased yield by 1590 kg ha–1 in season 1 and 1840 kg ha–1 in season 2. Thus, for the conditions studied here, it was rational to add fertiliser only in combination with irrigation and not in a rainfed system.

Effect of Water and Nutrient Supply on Photosynthesis and Yield of Energy Beet Genotypes

The responses of two energy beet (sugarbeet) genotypes, AR355 and AC211, to three (high, medium, and low) water and nutrient supply (WNS) regimes were investigated in an attempt to find an optimal water and nutrient rate for selected sugarbeet ( L.) genotypes. The results showed that photosynthesis rate (P N ), transpiration rate (E), and stomatal conductance (g s ) decreased with the reduction of WNS. As a consequence of the reduction in stomatal conductance, decline in the intercellular CO 2 concentration was also observed. The temperature difference between the leaf and air (T l - T a ) increased with the decrease of WNS. Under medium WNS, both genotypes had the highest sugar yield. Sugar yield was significantly affected by WNS, but it was not significantly influenced by genotype and the interaction between genotype and WNS. WNS, genotype, and the interaction between genotype and WNS had significant effects on the shoot/root ratio of sugarbeet. Irrigation water productivity based on sugar and fresh mass above ground were negatively correlated with WNS.

Yield, water use efficiency and economic analysis of energy sorghum in South Texas

Yields, water use efficiency and economic returns (net farm revenues) of biomass sorghum [Sorghum bicolor (L.) Moench] were investigated over two years (2012 and 2014) under limited water resource conditions. Energy sorghum was grown under four water supply regimes: rain-fed (or dry-land, level 1), 50% (level 2), 75% (level 3) and 100% (level 4) of crop evapotranspiration rates (% ETc). Biomass yields ranged from 5.8 to 16.6 Mg ha−1 (dry weight) after 126 days of growth. Average water use efficiencies ranged from 3.95 kg m−3 to 23.4 kg m−3. Net return was approximately 410 $ ha−1 with water depths above 400 ha-mm. These results suggest that it is possible to obtain more than 60 Mg ha−1 of sorghum biomass (wet basis) with at least 425 mm of water. While biomass yield under irrigation was greater than rain-fed conditions, there were no significant differences among irrigation treatments. Biomass chemical composition did not differ significantly among water treatments suggesting that biofuel quality would not be affected by water deficits.

Leaf traits, water stress, and insect herbivory: Is food selection a hierarchical process?

Plant water stress can affect selectivity by insect herbivores. Numerous studies have shown greater insect preference for water-stressed plants, but others have reported the opposite response. We evaluated leaf consumption by adults of Nyctelia circumundata (a chewing insect) in leaves of Larrea divaricata and Prosopis alpataco. Three bioassays (two-way choice tests) were performed: two intra-specific comparisons between well-watered (+W) and water-stressed (−W) leaves of each species and one inter-specific comparison between leaves of the two species. Leaf biomass was reduced by water stress in both species. Nitrogen concentration in leaves (N) was reduced by drought in P. alpataco. In contrast, total phenolics and specific leaf area (SLA) did not differ between treatments within species. Nyctelia circumundata did not show preference by any water supply regimes in intra-specific comparisons. In contrast, in inter-specific choice tests, it showed a marked preference for P. alpataco, which is the species with the highest nitrogen concentration and lowest total phenolics concentration. In intra-specific comparisons, maximum leaf consumption was inversely related to SLA in both species. Furthermore, in P. alpataco, N concentration was positively related to maximum leaf consumption and negatively related to leaf water content (LWC). In contrast, in inter-specific comparisons, total phenolics was negatively related to maximum leaf consumption, while N concentration exhibited the opposite trend. These results suggest that food selection is a hierarchical process where chemical attributes (i.e., total phenolics and N) are taken into account for species selection, and physical attributes (i.e., SLA and LWC) for choosing individuals inside species.

English

The elucidation of drought tolerance mechanisms in plants may facilitate the commercial exploitation of the species J. curcas in semi-arid regions. This study was designed to evaluate the growth and drought tolerance strategy of J. curcas plants grown under different water regimes. The work was carried out on an outdoor bench in full sunlight at Goias State University, following the completely randomized experiment design with a 2x2 factorial scheme (two wild populations of J. curcas , naturally found in the states of Sao Paulo and Goias, and two water supply regimes: 0% and 100% of evapotranspiration) and five replications. First a mixture of soil, sand and manure was prepared at the ratio of 3:1:0.5, respectively. The plants were irrigated daily, and at 60 days of age they were subjected to 10 days of water deficit and then rehydrated for five days. Under water deficit condition the J. curcas plants decreased the shoot growth, adjusted the leaf area to reduce the transpiration rate and increased the root system growth. J. curcas plants delay dehydration as a strategy to tolerate water deficit, for which the species reduces the transpiration rate and sustains tissue hydration using the water stored in the succulent stem.

Dominant clonal Eucalyptus grandis × urophylla trees use water more efficiently

Wood growth in trees depends on the acquisition of resources, and can vary with tree size leading to a variety of stand dynamics. Typically, larger trees obtain more resources and grow faster than smaller trees, but while light has been addressed more often, few case studies have investigated the contributions of water use and water use efficiency (WUE) within stands to isolate the tree-size dominance effect. Our sites were located near the cities of Aracruz and Eunapolis in Northeastern Brazil. We measured tree biomass growth, water use and WUE to explore patterns of growth among dominant and non-dominant trees in rainfed (1350mmyr−1) and irrigated experimental stands in two high productivity tropical clones of Eucalyptus grandis×urophylla growing in clayey Ultisol soils. During the study period, irrigation supplied an additional 607mm and 171mm at the Aracruz and Eunapolis sites respectively. We tested two hypotheses; (1) larger trees transpire more water, and produce more wood per water used (higher water use efficiency, WUE) than smaller trees of the same clone and; (2) this pattern also applies if a water surplus is added via irrigation to alleviate water stress.Across both sites, we measured stand water use using sap flow sensors from August to December, and quantified wood growth on a tree-basis and then derived WUE, in kg wood per m3 of water transpired. Dominant trees showed higher rates of tree growth, water use and WUE than dominated trees for the two sites-clones and under both water supply regimes. Using the rainfed trees at Aracruz as an example, 50-kg trees grew 1.0kgmonth−1 compared with growth of 100-kg trees of 3.8kgmonth−1. The smaller trees would use water in a rate of 2.1m3month−1, compared with 3.1m3month−1 for the larger trees, demonstrating a higher WUE for the larger tree (1.2kgm−3 versus 0.5kgm−3). Our results suggest that manipulating stand density on heterogeneous stands, e.g. thinning, has the potential to minimize the tradeoffs between wood growth and tree water use in Eucalyptus grandis×urophylla plantations, mainly in tropical regions with seasonal water deficit. However, more research is needed to discern the underlying mechanisms responsible for higher WUE exhibited by dominant trees and distinct clones.

The application for fertilizer–yield relationships of the ET–yield response factor equation

Many attempts have been made to understand the plant response to water using plant growth models. The effects of fertilizer on crop yield are greater than those of water. Therefore, some models that have been developed for the evaluation of water-yield relationships can also be used for fertilizer-yield relationships. The purpose of this study was to develop an equation to use in fertilizer applications similar to one used to evaluate crop production under adequate and deficit water supply regimes. The equation can be rewritten for the fertilizer consumed by plants instead of the evapotranspiration (ET). Sample applications showed that the resulting ET-yield response factor equation can be used successfully in the evaluation of fertilizer-yield relationships. Thus, the yield loss per unit of fertilizer deficiency can be determined more precisely by the equation.

Health as a sustainability indicator within water resources management in rural and peri-urban areas of central northern Namibia

In this paper, a modelling approach is presented which is able to analyze a water-supply regime in order to comprehend health-related aspects in water resources management. The area of investigation is the Cuvelai-Etosha Basin in central northern Namibia. Major health hazards for the rural and peri-urban population stem from the usage of unsafe water sources. In the systems analysis, the variable Health turned out to be one of the major sustainability indicators. Furthermore, the identification of cause–effect chains revealed that education is a key factor in improving users’ health situation, whereas poverty significantly degrades it.

Sectoral contributions to surface water stress in the coterminous United States

Here, we assess current stress in the freshwater system based on the best available data in order to understand possible risks and vulnerabilities to regional water resources and the sectors dependent on freshwater. We present watershed-scale measures of surface water supply stress for the coterminous United States (US) using the water supply stress index (WaSSI) model which considers regional trends in both water supply and demand. A snapshot of contemporary annual water demand is compared against different water supply regimes, including current average supplies, current extreme-year supplies, and projected future average surface water flows under a changing climate. In addition, we investigate the contributions of different water demand sectors to current water stress. On average, water supplies are stressed, meaning that demands for water outstrip natural supplies in over 9% of the 2103 watersheds examined. These watersheds rely on reservoir storage, conveyance systems, and groundwater to meet current water demands. Overall, agriculture is the major demand-side driver of water stress in the US, whereas municipal stress is isolated to southern California. Water stress introduced by cooling water demands for power plants is punctuated across the US, indicating that a single power plant has the potential to stress water supplies at the watershed scale. On the supply side, watersheds in the western US are particularly sensitive to low flow events and projected long-term shifts in flow driven by climate change. The WaSSI results imply that not only are water resources in the southwest in particular at risk, but that there are also potential vulnerabilities to specific sectors, even in the ‘water-rich’ southeast.

SILAGE MAIZE GROWTH SIMULATION USING PILOTE AND CROPSYST MODEL

ABSTRACTModels simulating the effects of water stress on crop growth can be valuable tools for improving water management. PILOTE, an operative crop model, and CropSyst, a more sophisticated one, are compared on the basis of the simulation of silage maize (Zea maize L.) growth for 2 years (2009–2010) under different water supply regimes in the semi‐arid climate of Tadla (Morocco). Both based on Beer's law via the intercepted potential active radiation (IPAR) regarding dry matter accumulation, the models differ in the level of complexity describing crop development, biomass growth, root water uptake principle and consequently, in the number of input parameters. The models were calibrated on an unstressed irrigation treatment in 2009, and were validated on other stressed and unstressed treatments in 2009 and 2010. Although PILOTE required fewer input parameters and data than CropSyst, it performed similarly and often better when simulating both biomass and soil water balance. Therefore, for water management purposes only, the use of a simpler model such as PILOTE can be recommended. Copyright © 2013 John Wiley &amp; Sons, Ltd.

Use of plant water relations to assess forage quality and growth for two cultivars of Napier grass (Pennisetum purpureum) subjected to different levels of soil water supply and temperature regimes

Napier grass (Pennisetum purpureum Schumach.) is an important fodder and relatively drought-tolerant crop in tropical and subtropical regions, especially in developing countries. For this and other species, tools are needed for identifying drought-tolerant cultivars to aid selection for semi-arid environments. We determined tissue water status, carbon assimilation, biomass yield and forage quality for Napier grass cvv. Bana and Atherton grown in bins and subjected to three soil-water supply levels (100, 50 or 25% of field capacity) in glasshouses set at either low (15−25°C) or high (25−35°C) temperature regimes, over three growing cycles. Our aim was to explore whether differences in leaf water potential (LWP) and carbon assimilation rates could be reliable indicators of the relative yield potential and forage quality of the two cultivars in environments prone to water and heat stresses. At the low soil-water supply of 25% and low temperature, Bana had lower (more negative) LWP and relative water content (RWC) than Atherton, while at 50% and 100% soil-water supply, Bana had a higher tissue water status. Under the high temperature regime, Bana had consistently more positive LWP and RWC than Atherton, but the differences were not significant. The two cultivars had a similar CO2 assimilation rate (A) and there were no significant differences in the total dry matter yields over the three growing cycles. Water-use efficiency for above-ground biomass (kg ha–1 mm–1) was similar for both cultivars and was 28.5–35.1 under the low temperature regime and 16.9–22.9 under the high temperature regime. Neutral detergent fibre (NDF) was often higher for Bana at low water supply and low temperature than for Atherton, but the trend was reversed under the high temperature regime. Digestibility was generally improved under water-stressed conditions, and there was a positive correlation between NDF and both LWP and RWC measured at midday, but only under the low temperature regime. We conclude that LWP, RWC and A, alone or together, are inadequate for selecting cultivars for dry and hot environments, because cultivars may differ in other mechanistic responses to water stress and high temperatures.

Nitrogen Accumulation, Retranslocation and Partitioning in Oats (&lt;i&gt;Avena&lt;/i&gt; L.) as Affected by Different Water Supply and Nitrogen Fertilization

In order to investigate the effect of water and nitrogen (N) supply on oat N accumulation, translocation and partitioning, we used two contrasting oat varieties, the naked Baiyan 2 (Avena nuda L.) and the hulled Baiyan 7 (Avena sativa L.) as experimental material, six treatment combinations, including 2 water supply regimes, no irrigation and 3 times irrigation and 3 levels of N application was 30, 90 and 150 kg N hm-2 were set in the experiment. The result showed that: At each growth stage, the N accumulation of Baiyan 2 was significantly higher than that of Baiyan 7 (p N3 &gt;N1.The N petitioning to grain of irrigation treatment was higher than that of no irrigation. Suitable N (N2, 90kg N hm-2) can increase grain N and also NHI increased. From the result, we can conclude that Baiyan 2 is a higher N efficiency cultivar. Irrigation increased the whole plant N accumulation and partitioning to grain.

Morphological and biomass characteristic acclimation of trident maple (Acer buergerianum Miq.) in response to light and water stress

Acer buergerianum Miq. (Trident maple) is a native species of China with a large distribution, but exist in small population. Water and light are two important factors limiting plant growth and are crucial in the framework of forest regeneration. However, there is no consensus on how shade interacts with drought. Four hypotheses in the recent literature variously predict that shade will have a stronger, weaker or equal impact on seedlings under drought stress. This study investigated the interactive responses of A. buergerianum to light and water focusing on seedling growth, leaf morphology and biomass partitioning by performing a growth experiment in pots with different water supply regimes [15, 35, 55, 75, 95 % of field capacity (FC)] combined with two light regimes (10 and 66 % of full sunlight). After 123 days treatment, the results showed that shade greatly reduced growth and biomass, in contrast enhancing the amount of chlorophyll, the amount of water in the leaves, and the specific leaf area. Drought reduced growth, biomass, and the bulk of the leaves. Most leaf traits and biomass characteristics had strong interactions in their responses to light and water treatments. Allometric analysis revealed that water and light had no effects on root to shoot ratios, main root to lateral root ratios, and root mass ratios. Shade alleviated the negative impact of drought. A. buergerianum successfully adapted to the various light and water conditions. We recommend a water supply above 15 % FC to keep the seedlings vigorous, under both sunlight conditions.

Water resources management in central northern Namibia using empirically grounded modelling

In this paper, a new methodology for the analysis and assessment of water supply regimes is presented. The problems of water supply management in developing countries are multidimensional and interdependent. Conventional methods, which only deal with separated and isolated issues, are not appropriate to deal with these problems. The method presented here, however, can comprehend the whole system. Therefore, using this method, conclusions for the management of adapted institutional and technological transformations can be drawn. In this study, relevant system variables of a problem context are identified, and their interdependencies are assessed and interpreted. This is done by using a method of qualitative interview analysis (grounded theory) and a cybernetic modelling approach (sensitivity analysis). In doing so, it is possible to identify outstanding variables which are essential to understand the system. These variables reveal the weakest links, driving forces, systemic stabilisers and the sustainability indicators of the system. The case study area is the Cuvelai-Etosha-Basin in central northern Namibia where a large-scale water supply system has been established. The water supply in the region is determined by the dependence on external water resources, high precipitation variability, absence of perennial rivers, saline groundwater, population growth and urbanisation.