Showing papers on "Water use published in 2003"

Development and testing of the WaterGAP 2 global model of water use and availability

Abstract: Growing interest in global environmental issues has led to the need for global and regional assessment of water resources. A global water assessment model called "WaterGAP 2" is described, which consists of two main components—a Global Water Use model and a Global Hydrology model. These components are used to compute water use and availability on the river basin level. The Global Water Use model consists of (a) domestic and industry sectors which take into account the effect of structural and technological changes on water use, and (b) an agriculture sector which accounts especially for the effect of climate on irrigation water requirements. The Global Hydrology model calculates surface runoff and groundwater recharge based on the computation of daily water balances of the soil and canopy. A water balance is also performed for surface waters, and river flow is routed via a global flow routing scheme. The Global Hydrology model provides a testable method for taking into account the effects of climate and land cover on runoff. The components of the model have been calibrated and tested against data on water use and runoff from river basins throughout the world. Although its performance can and needs to be improved, the WaterGAP 2 model already provides a consistent method to fill in many of the existing gaps in water resources data in many parts of the world. It also provides a coherent approach for generating scenarios of changes in water resources. Hence, it is especially useful as a tool for globally comparing the water situation in river basins.

Rice production in water-scarce environments

Abstract: Rice production in Asia needs to increase to feed a growing population. Though a complete assessment of the level of water scarcity in Asian rice production is still lacking, there are signs that declining quality of water and declining availability of water resources are threatening the sustainability of the irrigated rice-based production system. Drought is one of the main constraints for high yield in rain-fed rice. Exploring ways to produce more rice with less water is essential for food security and sustaining environmental health in Asia. This chapter reviews the International Rice Research Institute (IRRI)’s integrated approach, using genetics, breeding and integrated resource management to increase rice yield and to reduce water demand for rice production. Water-saving irrigation, such as saturated-soil culture and alternate wetting and drying, can drastically cut down the unproductive water outflows and increase water productivity. However, these technologies mostly lead to some yield decline in the current lowland rice varieties. Other new approaches are being researched to increase water productivity without sacrifice in yield. These include the incorporation of the C4 photosynthetic pathway into rice to increase rice yield per unit water transpired, the use of molecular biotechnology to enhance drought-stress tolerance and the development of ‘aerobic rice’, to achieve high and sustainable yields in non-flooded soil. Through the adoption of water-saving irrigation technologies, rice land will shift away from being continuously anaerobic to being partly or even completely aerobic. These shifts will have profound changes in water conservation, soil organic-matter turnover, nutrient dynamics, carbon sequestration, soil productivity, weed ecology and greenhouse-gas emissions. Whereas some of these changes can be perceived as positive, e.g. water conservation and decreased methane emission, some are perceived as negative, e.g. release of nitrous oxide from the soil and decline in soil organic matter. The challenge will be to develop effective integrated natural-resource-management interventions, which allow profitable rice cultivation with increased soil aeration, while maintaining the productivity, environmental services and sustainability of rice-based ecosystems.

Water Productivity in Agriculture: Limits and Opportunities for Improvement

Abstract: A water productivity framework for understanding and action economics of water productivity in managing water for agriculture the concept of efficiency in water resources management and policy rice production in water-scarce environments managing saline and alkali water for higher productivity opportunities for increasing water productivity of CGIAR crops through plant breeding and molecular biology world water productivity - current situation and future options improving water productivity through deficit irrigation - examples from Syria, North China Plain and Oregon, USA.

Reliance on stored water increases with tree size in three species in the Pacific Northwest.

Abstract: In tall old forests, limitations to water transport may limit maximum tree height and reduce photosynthesis and carbon sequestration. We evaluated the degree to which tall trees could potentially compensate for hydraulic limitations to water transport by increased use of water stored in xylem. Using sap flux measurements in three tree species of the Pacific Northwest, we showed that reliance on stored water increases with tree size and estimated that use of stored water increases photosynthesis. For Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), water stored in xylem accounted for 20 to 25% of total daily water use in 60-m trees, whereas stored water comprised 7% of daily water use in 15-m trees. For Oregon white oak (Quercus garryana Dougl. ex Hook.), water stored in xylem accounted for 10 to 23% of total daily water use in 25-m trees, whereas stored water comprised 9 to 13% of daily water use in 10-m trees. For ponderosa pine (Pinus ponderosa Dougl. ex Laws.), water stored in xylem accounted for 4 to 20% of total daily water use in 36-m trees, whereas stored water comprised 2 to 4% of daily water use in 12-m trees. In 60-m Douglas-fir trees, we estimated that use of stored water supported 18% more photosynthesis on a daily basis than would occur if no stored water were used, whereas 15-m Douglas-fir trees gained 10% greater daily photosynthesis from use of stored water. We conclude that water storage plays a significant role in the water and carbon economy of tall trees and old forests.

Comparison of water status indicators for young peach trees

Abstract: We measured a series of physiological and physical indicators and compared them to xylem sap flow, to identify the most sensitive and reliable plant water status indicator. In the growing season of 1998, 4-year-old peach trees (Prunus persica Batsch cv. 'Suncrest', grafted on 'GF 677' rootstock) were studied under two irrigation treatments, 25 l day−1 and no irrigation, and during recovery. Trials were conducted near Pisa (Italy) in a peach orchard situated on a medium clay loam soil and equipped with a drip-irrigation system (four 4 l h−1 drippers per tree). Measurements of leaf water potential (Ψ W ), stem water potential (Ψ S ), and leaf temperature (T l) were taken over 5 days (from dawn to sunset) and analyzed in conjunction with climatic data, sap flow (SF), trunk diameter fluctuation (TDF) and soil water content (SWC). Physiological indicators showed substantial differences in sensitivity. The first indication of changes in water status was the decrease of stem radial growth. TDF and SF revealed significant differences between the two irrigation treatments even in the absence of differences in pre-dawn leaf water potential (pdΨW), up until now widely accepted as the benchmark of water status indicators. Irrigated trees showed a typical trend in SF rate during the day, while in non-irrigated plants the maximum peak of transpiration was anticipated. Measurements of water potential showed ΨS to be a better indicator of tree water status than ΨW. T l was found to have poor sensitivity. In conclusion, we found the sensitivity of the indicators from the most to the least was: TDF >SF rate >SF cumulated = pdΨW=ΨS>mdΨW>T l.

Water use efficiency and sustainability of different long-term crop rotation systems in the Loess Plateau of China

Abstract: In the dryland region of the Loess Plateau in China, improved soil and water conservation practices are essential for sustainable agriculture. The prevailing cropping practice in this region, growing winter wheat (Triticum aestivum L.) as a monoculture, carries two major drawbacks which arise during the fallow period from July to September: firstly, an exposure to soil erosion from rainstorms and, secondly, poor water storage efficiency of rain. Alternative cropping systems were therefore investigated. They comprised four rotations, each of 3 or 4 years, involving different combinations of corn (Zea mays L.), wheat, broomcorn millet (Panicum miliaceum), and pea (Pisum sativum L.). The water use efficiencies (WUEs) and sustainability of the rotations were evaluated at Changwu Agri-ecological Station in the Loess Plateau from 1984 to 1996. Results showed that two of the rotations gave significantly improved grain yields and WUE compared to the standard wheat monoculture. The rotation of corn, wheat, and wheat–millet could increase the duration of crop coverage during the rainy season from a low of 38% of the time for wheat to a maximum of 80%, and the crop precipitation interception index (CPII) from 53% for wheat to a maximum of 73%. All the alternative rotations tested did not significantly affect available soil water at wheat planting. Considering all factors, a 3-year rotation of corn, wheat, and wheat–millet was found to offer the best potential for improving cropping practice in the region.

Water Dynamics in Plant Production

Abstract: 1: The Role of Water in Plant Life 1.1: Functions of Water in the Plant Box 1.1: Light and water - prerequisites of photosynthesis 1.2: Adaptation Strategies of Plants to Overcome Water Shortage 1.3: Water and Net Primary Production 1.4: Water and Type of Vegetation 2: The Role of Water in Soil 2.1: Soil Genesis and Soil Functions 2.2: Soil Fauna and Vegetation Cover 3: The Interdependence of Soil Water and Vegetation 3.1: The Significance of the Soil for Water Storage 3.2: Transpiration and Seepage of Water with Different Types of Vegetation 4: Properties and Energy State of Water 4.1: Physical-Chemical Properties 4.2: The Concept of Water Potential and the Darcy Equation 5: Water Storage and Movement in Soil 5.1: Fundamentals and Principles Box 5.1: Measuring soil water 5.2: Evaporation 5.3: Infiltration and Water Transport Box 5.2: Soil structure and preferential flow 6: The Root - the Plant's Organ for Water Uptake 6.1: The Role of the Root in the Plant 6.2: Structure of the Root Tip Box 6.1: Methods of studying roots 6.3: Root Systems 7: The Water Balance of the Plant 7.1: Water Potentials in Plant Cells 7.2: Water Uptake by Roots Box 7.1: Early experiments for determining water suction and water pressure of roots 7.3: Transpiration by Leaves 7.4: The Action of Stomatal Guard Cells 7.5: Water Transport within the Plant 7.6: Water Potentials in Plants Box 7.2: Searching for the cause of sap ascent 8: The Plant as a Link between Soil and Atmosphere:an Overview 8.1: The Soil-Plant-Atmosphere Continuum (SPAC) 8.2: Potential Evapotranspiration Box 8.1: Potential evaporation 8.3: Relations between Potential Evapotranspiration, Soil Water and Transpiration 9: Water Use by Crops 9.1: Growth of Roots and leaves 9.2: Leaf Area Index (LAI) and Transpiration 9.3: Root System Development and Water Uptake 9.4: How Much of the Soil Water is Extractable by Plant Roots? 9.5: Stomatal Control of Water Vapour Loss 9.6: Water Use Throughout the Growing Season 9.7: How to Determine the Components of the Field Water Balance 9.8: Numerical Simulation Box 9.1: How lysimeters work Box 9.2: Measurement of water flow through plants 10: Radiation and Dry Matter Production 10.1: Radiation and Net Photosynthesis of Single Leaves 10.2: Radiation Interception and Dry Matter Accumulation in Crop Stands 11: Water Use and Dry Matter Production 11.1: Relations and their Optimization Box 11.1: The saturation deficit of the air determines transpiration efficiency 11.2: The Transpiration Ratio and a Related Standard 11.3: Water Use and an Estimate of Dry Matter Production 12: Influence of Nutrient Supply on Water Use and Establishment of Yield 12.1: Yield Dependency on Water and Nutrient Supply 12.2: Influence of Nutrient Supply on the Relationship between Water Use and Yield 12.3: Transpiration Efficiency and Fertilizer Application 13: Development of Economic Yield under Inadequate Water Supply 13.1: Physiological Reactions and Assimilate Partitioning 13.2: Economic Yield 13.3: Water Shortage at Different Phenological Stages 13.4: Relation between Water Use and Economic Yield in Principal Crops 14: Water Stress in Plants 14.1: Measuring Water Stress in Plants 14.2: How Plants Perceive Water Stress Box 14.1: Signalling between roots and shoots 15: Climatic Factors Influencing Yield 15.1: Growth-limiting Climatic Factors 15.2: Climate Change 15.3: Plants, Soils and Cropping Pattern in a Changing Environment 16: Breeding for Yield and Water Use 16.1: Comparing Old and New Cultivars 16.2: Future Strategies in Plant Breeding 16.3: Application of Molecular Biology to Improve Crop Performance under Drought 17: Controlling the Soil's Water Balance by Soil Management 17.1: Which of the Balance Components can be Changed? 17.2: Controlling Infiltration 17.3: Controlling Evaporation 17.4: Increasing the Quantity of Extractable Soil Water Box 17.1: Collection of water south of Sahel: a man, a hoe and barren land 17.5: Conservation Tillage 18: Controlling Water Use by Crop Management 18.1: Crop Rotation 18.2: Choice of Species and Cultivars 18.3: Seeding and Stand Density 18.4: Fertilizer Application 19: Irrigation 19.1: Need, Concerns, Problems 19.2: Tapping Water - the Basis of Early Civilizations 19.3: Water Requirement of Crops 19.4: Timing and Adjusting the Application of Water 19.5: Efficient Water Use 19.6: Irrigation Methods 20: Epilogue

Water Resources Management

Abstract: The world's water resources are being tapped at an ever increasing rate, to the extent that sustainability and water quality are being compromised. This book provides accounts of the technology used for managing water resources to reduce risks. Besides controlling floods, overcoming droughts and reducing pollution, the reader will learn to plan and maintain hydraulic structures, and to appreciate the diverse demands on water, including those of the environment. The topics considered include hydrology and assessment of water resources; drought management and flood management tools; and the interaction between land use and water resources, including surface runoff, groundwater and water quality. The second half of the book focuses on water use, demand management and the infrastructure required to manage water. Consideration is also given to the tools needed for planning, including economics and computer modelling. This book is aimed at a postgraduate level, suitable for students in water engineering and science. It will also serve as a reference for practitioners concerned with water resources and water supply.

Physical and economic efficiency of water use in the river basin: Implications for efficient water management

Abstract: [1] With growing water scarcity and increasing competition across water-using sectors, the need for water savings and more efficient water use has increased in importance in water resources management. Improvement in the physical efficiency of water use is related to water conservation through increasing the fraction of water beneficially used over water applied, while enhancing economic efficiency is a broader concept, seeking the highest economic value of water use through both physical and managerial measures. Physical and economic efficiency measures are both useful indicators for water management at the irrigation system and river basin level. However, the relationship between physical efficiency and economic efficiency is not always clear, and the values of these measures may indicate different directions for water policy and investments in irrigation. Open research questions include, for example, the following: How does the change in responsiveness of water allocation and irrigation technology to economic incentives affect physical and economic irrigation efficiency? What is the impact of a change in irrigation system efficiency on basin physical and economic efficiency? How do changes in water withdrawals affect basin physical and economic efficiency under a given water requirement? To explore these issues, an integrated economic-hydrologic river basin model is applied to the Maipo River Basin in Chile. A series of modeling scenarios is defined, and policy implications based on changes in physical and economic efficiencies for basin-wide irrigation water management are analyzed.

Water resource partitioning, stem xylem hydraulic properties, and plant water use strategies in a seasonally dry riparian tropical rainforest.

Abstract: This study investigated seasonal variation in the origin of water used by plants in a riparian tropical rainforest community and explored linkages between plant water source, plant xylem hydraulic conductivity and response to the onset of dry conditions. The study focused on five co-dominant canopy species, comprising three tree species (Doryphora aromatica, Argyrodendron trifoliolatum, Castanospora alphandii) and two climbing palms (Calamus australis and Calamus caryotoides). Stable isotope ratios of oxygen in water (δ18O) from soil, groundwater, stream water and plant xylem measured in the wet season and the subsequent dry season revealed water resource partitioning between species in the dry season. Measurement of stem-area-specific hydraulic conductivity (K S) in the wet season and subsequent dry season showed a significant dry-season loss of K S in three of the five species (Castanospora alphandii, Calamus australis and C. caryotoides) and a decrease in mean K S for all species. This loss of hydraulic conductivity was positively correlated with the difference between wet-season and dry-season midday leaf water potentials and with leaf carbon isotope discrimination, indicating that plants that were less susceptible to loss of conductivity had greater control over transpiration rate and were more water-use efficient.

China'S Agricultural Water Policy Reforms: Increasing Investment, Resolving Conflicts, And Revising Incentives

Abstract: Water shortages in important grain-producing regions of China may significantly affect China's agricultural production potential and international markets. Falling ground-water tables and disruption of surface-water deliveries to important industrial and agricultural regions have provoked concern that a more dramatic crisis is looming unless effective water conservation policies can be put into place rapidly. While China's water use is unsustainable in some areas, there is substantial capacity to adapt and avert a more serious crisis. Recent changes in water management policies may serve to bring about more effective water conservation. This report provides an overview of these changes and some analysis of their effectiveness. Wheat is the most likely crop to show a fall in productiondue to water shortages, but cotton, corn, and rice may also be affected.

Sap flow of three co-occurring Mediterranean woody species under varying atmospheric and soil water conditions

Abstract: We studied the seasonal patterns of water use in three woody species co-occurring in a holm oak forest in northeastern Spain. The three species studied, Quercus ilex L., Phillyrea latifolia L. and Arbutus unedo L., constitute more than 99% of the total basal area of the forest. The study period included the dry seasons of 1999 and 2000. Water use was estimated with Granier-type sap flux sensors. Standard meteorological variables, soil water content and leaf water potentials were also monitored. All monitored individuals reduced leaf-related sap flow (Q(l)) during the summer, concurrent with an increase in soil moisture deficit (SMD). Despite similar maximum Q(l) between species, the decline in Q(l) with increasing SMD was species-dependent. The average reduction in Q(l) between early summer and the peak of the drought was 74% for A. unedo (n = 3), 58% for P. latifolia (n = 3) and 87% for Q. ilex (n = 1). The relationship between canopy stomatal conductance (G(s)) and vapor pressure deficit (D) changed during the course of the drought, with progressively lower G(s) for any given D. Summertime reductions of Q(l) and G(s) were associated with between-species differences in vulnerability to xylem embolism, and with the corresponding degree of native embolism (lowest in P. latifolia and highest in Q. ilex). Our results, combined with previous studies in the same area, outlined differences among the species studied in manner of responding to water shortage, with P. latifolia able to maintain water transport at much lower water potentials than the other two species. In an accompanying experiment, A. unedo responded to an experimental reduction in water availability by reducing Q(l) during the summer. This species also modified its water use between years according to the different seasonal patterns of precipitation. These results are discussed in relation to the possible impacts that climate change will have on Q. ilex-dominated forests.

Watershed development: A solution to water shortages in semi-arid India or part of the problem?

Abstract: There have been dramatic changes in the hydrology of many of the dry areas of South India in recent years as a result of increased groundwater-based irrigation, watershed development and land use change. Although intensive development of water resources has brought about huge benefits, its very success has thrown up new challenges. Demand and competition for water has increased to the extent that — in some areas — current levels of annual water use are so high that, in all but the wettest years, annual water use approximates towards annual replenishment of surface and ground water resources. In these areas, it is clear that the emphasis should switch from development to the management of water resources to ensure that water is allocated to activities with the highest economic and social value. Although current watershed development programmes bring a range of benefits, they may also change the temporal and spatial pattern of water availability and use. This can result in significant negative trade-offs such as more unreliable domestic water supplies in ‘downstream’ areas, particularly during low rainfall or drought years. As part of the Karnataka Watershed Development Project (KAWAD), a water resource audit assessed the status of water resources in the project watersheds and identified resource management practices that should be promoted by the project. This paper summarises the audit’s findings and recommendations, the main lessons learned and progress to date in implementing recommendations. For comparison, findings and recommendations from a water audit in southern Andhra Pradesh are also summarised.

Securing water for people, crops, and ecosystems: New mindset and new priorities

Abstract: A fundamentally new approach to water and human development will be needed during this new century if we are to secure sufficient freshwater to meet the needs of some 9 billion people while at the same time protecting the critical ecosystem services upon which the human economy depends. Signs of unsustainable water use — including falling water tables, shrinking lakes, and the drying up of rivers and streams — are widespread and spreading. In many regions, greater modification and appropriation of freshwater systems for human purposes will yield greater costs than benefits and create the risk of irreversible losses of species and ecosystem services. A new mindset is needed to guide water use and management in this new century, one that views the human water economy as a subset of nature’s water economy. Living within nature’s limits will require that societies satisfy the basic needs of people and ecosystems before non-essential water demands are met. It will require on the order of a doubling of water productivity. And it will require stronger institutions to encourage equitable sharing of water to alleviate tensions within and between countries.

Economics of water productivity in managing water for agriculture

Abstract: In Kijne, J. W.; Barker, R.; Molden. D. (Eds.). Water productivity in agriculture: limits and opportunities for improvement. Wallingford, UK: CABI; Colombo, Sri Lanka: International Water Management Institute (IWMI)Comprehensive Assessment of Water Management in Agriculture Series 1

China's agricultural water policy reforms: increasing investment, resolving conflicts, and revising incentives

Abstract: Water shortages in important grain-producing regions of China may significantly affect China's agricultural production potential and international markets. Falling ground-water tables and disruption of surface-water deliveries to important industrial and agricultural regions have provoked concern that a more dramatic crisis is looming unless effective water conservation policies can be put into place rapidly. While China's water use is unsustainable in some areas, there is substantial capacity to adapt and avert a more serious crisis. Recent changes in water management policies may serve to bring about more effective water conservation. This report provides an overview of these changes and some analysis of their effectiveness. Wheat is the most likely crop to show a fall in productiondue to water shortages, but cotton, corn, and rice may also be affected.

A comparison of water quality indices for coastal water.

Abstract: The present article discusses and compares five different water quality indices, viz arithmetic water quality index, multiplicative water quality index, unweighted arithmetic water quality index, unweighted multiplicative water quality index, and Harkin's water quality index, which were considered for characterizing the coastal water quality at the Jawaharlal Nehru Port Trust, Bombay, India. Dissolved oxygen, pH, biochemical oxygen demand (BOD), temperature, suspended solid, and turbidity were used as the parameters of water quality indices. The value function graphs used for above-mentioned variables were developed using harbour water quality standards and aquatic life. The product moment correlation coefficients for various water quality indices were determined using the SPSS software package to evaluate correlation among various indices. It was found that the unweighted arithmetic water quality index was higher than weighted arithmetic water quality index while the multiplicative water quality index was lower than unweighted multiplicative water quality index. All the indices were well correlated with each other except Harkin's water quality index. The Harkin's water quality index was different from other water quality indices. The comparison of different form of indices showed that the multiplicative water quality index was the most suitable water quality index for coastal waters.

Evaporation characteristics of wetlands: experience from a wetgrassland and a reedbed using eddy correlation measurements

Abstract: . Measurements of evaporation were made from July to November 1999 using the eddy correlation method on two wetland types – wet grassland and reedbeds – in south west England. The evaporative water use of a reed bed exceeded that of the grassland wetland by 15% (or 50 mm over the 5 months). The evaporation rates at both sites exceed of the Penman Potential Evaporation estimates calculated for this area. The difference between sites results from the higher roughness length of the reed bed and the lower effective surface resistance of the reed/open water assemblage. At the grassland site, a significant relationship between the surface resistance and water table level has been demonstrated. The water table at this site is managed to maintain the plant diversity and allow some agricultural access. This regime specifies a water table below the surface during the summer period, which results in higher surface resistances and lower evaporation. The results have important implications for local water resources management, especially where wetlands are maintained by pumping from rivers or groundwater. Keywords: wetlands, evaporation, eddy correlation, wet grassland, reedbed, vapour pressure, water table level