Hydrological impacts of rainwater harvesting (RWH) in a case study catchment: The Arvari River, Rajasthan, India: Part 2. Catchment-scale impacts

A key question in relation to rainwater harvesting (RWH) is whether the technique increases the sustainability of irrigated agriculture. A conceptual water balance model, based on field data from the Arvari River catchment, was developed to study and understand catchment-scale trade-offs of rainwater harvesting (RWH). The model incorporates an effective representation of RWH function and impact, and works on a daily time step. Catchment spatial variability is captured through sub-basins. Within each sub-basin hydrological response units (HRUs) describe the different land use/soil combinations associated with the case study catchment, including irrigated agriculture. Sustainability indices, based on irrigated agriculture water demand, were used to compare conceptual management scenarios. The results show that as RWH area increases, it reaches a limiting capacity from where additional RWH structures do not increase the benefit to groundwater stores, but reduces stream flow. If the irrigation area is increased at the optimal level of RWH, where the sustainability indices were greatest, the resilience of the system actually decreased. Nevertheless RWH in a system increased the overall sustainability of the water resource for irrigated agriculture, compared to a system without RWH. Also RWH provided a slight buffer in the groundwater store when drought occurred. The conceptual analysis highlights the important link between irrigation area and RWH area, and the impact of RWH on the catchment water balance.     

Managing water in rainfed agriculture—The need for a paradigm shift

Rainfed agriculture plays and will continue to play a dominant role in providing food and livelihoods for an increasing world population. We describe the world's semi-arid and dry sub-humid savannah and steppe regions as global hotspots, in terms of water related constraints to food production, high prevalence of malnourishment and poverty, and rapidly increasing food demands. We argue that major water investments in agriculture are required. In these regions yield gaps are large, not due to lack of water per se, but rather due to inefficient management of water, soils, and crops. An assessment of management options indicates that knowledge exists regarding technologies, management systems, and planning methods. A key strategy is to minimise risk for dry spell induced crop failures, which requires an emphasis on water harvesting systems for supplemental irrigation. Large-scale adoption of water harvesting systems will require a paradigm shift in Integrated Water Resource Management (IWRM), in which rainfall is regarded as the entry point for the governance of freshwater, thus incorporating green water resources (sustaining rainfed agriculture and terrestrial ecosystems) and blue water resources (local runoff). The divide between rainfed and irrigated agriculture needs to be reconsidered in favor of a governance, investment, and management paradigm, which considers all water options in agricultural systems. A new focus is needed on the meso-catchment scale, as opposed to the current focus of IWRM on the basin level and the primary focus of agricultural improvements on the farmer's field. We argue that the catchment scale offers the best opportunities for water investments to build resilience in small-scale agricultural systems and to address trade-offs between water for food and other ecosystem functions and services.     

Economic analysis of rainwater harvesting and irrigation methods, with an example from China

The purpose of this paper is to evaluate the economic feasibility of agriculture with rainwater harvesting and supplemental irrigation in a semiarid region. The results show the importance of making full use of every open-air hardened surface to collect rainwater and to establish rainwater catchment areas by utilizing unoccupied land. The results also show that the usefulness of the harvested rainwater is enhanced when water saving and prevent seepage techniques are employed. The results indicate that in order to maximize investment it is essential to select crops with a water requirement process that coincides with local rainfall events. Potato was found to be the most suitable crop in the studied region. The economic indices for potato were superior to spring wheat, corn and wheat/corn intercropping. Therefore, potato production using rainwater harvesting and supplemental irrigation is the best alternative for cropping systems in the semiarid region of Gansu, China.     

Least cost land-use changes for targeted catchment salt load and water yield impacts in south eastern Australia

This study reports an analysis of the economics of options for strategic land-use change to attain future catchment level target combinations of salt load and water yield. Farm level survey information on land use, productivity, prices and costs of production were integrated with spatially specific soil, rainfall, topography, hydrology and salinity results of the simulation model CAT (Catchment Analysis Tool). This information was used to populate a two stage economic optimization model in which subcatchment economic results were combined for catchment level analyses. This study is the first to exploit CAT results in an economic framework and the first in which economic results are mapped using CAT. The 64,000 ha Bet Bet Catchment in Victoria, Australia, once deemed among the highest priority areas in the Murray Darling Basin for dryland salinity reduction, is the focus of this study. The calculated current net present value (NPV) of agricultural production in the catchment is AU$ 78 million³ while providing 42 GL of water yield⁴ annually for use downstream with a salt load of 22,600 t. Results show that salt loads may be reduced to 18,600 t (reduction of 4000 t) through expansion of tree plantations and lucerne production, reducing water yield to 31 GL (11 GL reduction) and NPV to AU$ 63 million (AU$ 15 million reduction). Water yields could be increased from current levels by 2 GL while maintaining current salt loads. Alternatively, catchment NPV could be increased by approximately AU$ 7 million with little or no reduction in water yield; but there may be reasons (small farm size) why this is unlikely. For this catchment, the maximum reduction in salt load appears insufficient to justify public investment in tree planting and perennial pasture establishment, particularly when the reduced NPV and reduced water yields are taken into account. The results for this catchment do not support regulation of land use for the sake of lowering river salinity. However, the capacity of tree plantations to reduce water yields may support a regulation requiring purchase of water entitlements from downstream entitlement holders for new plantations. Despite millions of dollars of past public investment, it is now clear that Bet Bet Catchment was never one where land-use changes could benefit downstream water users. The approach described in this paper enables catchment management authorities to weigh costs of land-use change against downstream benefits and natural resource management (NRM) options elsewhere.     

黄河下游工程建设模糊综合决策优化排序研究

依据黄河下游沿黄地区各类工程建设与投资计划特点,将黄河下游工程建设分为防洪堤防、引黄工程、灌溉与节水、水土保持、生态环境、河口综合开发治理、水利信息化及重点水库等8类,利用模糊决策分析理论和工程规划调查数据确定工程权重,建立模糊理想点法模型,将黄河下游按照区域特征分为15个子区,利用所建立的模型进行排序求解,得到了黄河下游水利工程建设排序计划方案。研究成果对于黄河下游沿黄地区各类水利工程建设具有指导意义。     

An integrated hydro-economic modelling framework to evaluate water allocation strategies I: Model development

In this paper an integrated modelling framework for water resources planning and management that can be used to carry out an analysis of alternative policy scenarios for water allocation and use is described. The modelling approach is based on integrating a network allocation model (REALM) and a social Cost Benefit economic model, to evaluate the physical and economic outcomes from alternative water allocation policies in a river basin or sub-basin. From a hydrological perspective, surface and groundwater models were first applied to assess surface and groundwater resource availability. Then an allocation model was applied to reconcile the calculated surface and groundwater resources. From an economic perspective initially the value of water allocated to different uses in each demand centre within the system was estimated. These values were then placed in a social Cost Benefit Analysis to assess the economic consequences of different allocation scenarios over time and space. This approach is useful as it allows policymakers to consider not only the physical dimensions of distributing water, but also the economic consequences associated with it. This model is considered superior to other models as water is increasingly being seen as an economic good that should be allocated according to its value. The framework outlined in this paper was applied to the Musi sub-basin located in the Krishna Basin, India. In applying this framework it was concluded that competition for Musi water is very high, the transfer of water from agriculture to urban users is likely to grow in future and the value of water used in different agricultural zones is very low.     

Evaluation of soil water storage efficiency for rainfall harvesting on hillslope micro-basins built using time domain reflectometry measurements

Micro-basins are slope management structures built out of earth and stones on hillslopes around cultivated trees (e.g., olive trees) for the harvesting of rainfall and runoff water, and for the rehabilitation of land degraded by water erosion.In this study, the results of an experimental survey for the comparison of soil water content for both inside and outside the micro-basins are analyzed. Measurements are taken after some rainfall events from January to December 2003 in a hilly region of Central Tunisia. The time domain reflectometry technique is used to measure soil moisture in 15 sets of soil profiles (inside and outside) at three different depths. Four different soils are evaluated, i.e., Cambisols, Kastanozems, Arenosols, and Calcisols.The data analysis shows a significant improvement on the water stock obtained by this type of management. The differences in water storage with respect to soil type, depths, and tillage are evident, but strongly connected to farm management. For optimal management conditions an important increase of average water stock is observed; however, for bad or no farm management the amelioration is zero or is even deteriorating the state of vegetation.     

基于水权理论的新疆玛纳斯河水资

新疆玛纳斯流域是新疆最大的绿洲农耕区,该流域自然环境特点和社会经济发展在新疆均具有典型的代表性。玛纳斯河水权分配是玛纳斯河水资源管理改革的重要部分。首先探讨了水权的基本理论和使用权的分配原则,并依据这些原则,构建了水权分配的指标体系。为解决这一多地区多目标的决策问题,本文建立了多层系统半结构性多目标模糊优选的水权分配模型。采用该方法对玛纳斯河水权进行了分配,获得了较为合理的结果。     

Estimating the potential of rainfed agriculture in India: Prospects for water productivity improvements

A detailed district and agro-ecoregional level study comprising the 604 districts of India was undertaken to (i) identify dominant rainfed districts for major rainfed crops, (ii) make a crop-specific assessment of the surplus runoff water available for water harvesting and the irrigable area, (iii) estimate the efficiency of regional rain water use and incremental production due to supplementary irrigation for different crops, and (iv) conduct a preliminary economic analysis of water harvesting/supplemental irrigation to realize the potential of rainfed agriculture. A climatic water balance analysis of 225 dominant rainfed districts provided information on the possible surplus runoff during the year and the cropping season. On a potential (excluding very arid and wet areas) rainfed cropped area of 28.5 million ha, a surplus rainfall of 114 billion m³ (Bm³) was available for harvesting. A part of this amount of water is adequate to provide one turn of supplementary irrigation of 100 mm depth to 20.65 Mha during drought years and 25.08 Mha during normal years. Water used in supplemental irrigation had the highest marginal productivity and increase in rainfed production above 12% was achievable even under traditional practices. Under improved management, an average increase of 50% in total production can be achieved with a single supplemental irrigation. Water harvesting and supplemental irrigation are economically viable at the national level. Net benefits improved by about threefold for rice, fourfold for pulses and sixfold for oilseeds. Droughts have very mild impacts on productivity when farmers are equipped with supplemental irrigation.     

Water demand and flows in the São Francisco River Basin (Brazil) with increased irrigation

Most activities that support economic growth in the São Francisco River Basin (Brazil) need water. Allocation of the water resources to each competing use needs quantification in order to develop an integrated water management plan. Irrigation agriculture is the largest water consuming activity in the basin. It has produced large economic and social advancements in the region and has potential for further development. The local development agency in the São Francisco River has projected an increase of more than 500,000 ha in irrigation developments distributed within the basin.Water requirements of the projected irrigation expansions and their effects on river flow were quantified. A semi-distributed model was constructed to simulate the water balance in 16 watersheds within the basin. The watersheds were hydrologically characterized by the average precipitation, atmospheric demand and runoff as well as their variability. Water requirements for increased irrigated agriculture were calculated using an agronomic mass balance. A Monte Carlo procedure generated the variability of irrigation requirements and resulting decreased river flows from the multidimensional probability distribution of the hydrologic variables of each watershed.Irrigation requirements were found to be more variable during the wet season because of weather variability. In contrast to what might be expected, in drier years, irrigation requirements were often larger during the wet season than in the dry season because the cropped area is largest in the wet months and variability of precipitation is greater. Increased irrigation shifted downward the distribution of river flows but not enough to affect other strategic water uses such as hydropower. Further irrigation expansion may be limited by wet season flows.     

Fisheries and water productivity in tropical river basins: Enhancing food security and livelihoods by managing water for fish

Faced with growing pressure upon freshwater resources, increased water productivity in agriculture is essential. Efforts to do so however need to consider the wider role of water in sustaining food production. This paper considers the importance of water management in sustaining fish production in tropical river basins, and the potential for enhancing food production and income to farmers by integrating fish production into some farming systems. Specific examples from selected river systems and irrigated farming systems in Africa and Asia are provided. These highlight the benefits of integrating the water requirements for fish into water allocation decisions. In some cases, these benefits can be realised without any reduction in the water available for other purposes, while in others, a trade-off needs to be considered. The nature of these trade-offs needs to be better understood for better decision making in water management.     

北方农业雨水利用实践与发展前景展望

分析了北方雨水利用的现状,对国内雨水利用技术理论和实践以及国外较成功的经验作了详细的介绍。对雨水的自然利用和集雨农业中的降雨集流技术、雨水贮存净化技术、高效利用技术进行了概述。在北方地区进行集雨灌溉,合理发展集雨农业,既可以缓解灌溉水源紧张的局面,提高农业生产力,又可以减少雨水对土壤的侵蚀和水土流失,有助于北方农业可持续发展,具有广阔的发展前景。     

农业综合开发项目灌排水渠道水力断面有关参数的确定与探讨

无论是中低产田改造项目还是山区小流域治理项目的施工设计阶段,均不可避免的涉及到灌排水渠道的纵横断面设计,而灌排水渠道横断面设计则主要通过渠道水力断面计算确定水力最佳断面结构型式,并分析如何由已确定的水力最佳断面相关参数进一步确定实用经济断面构型式。工程设计中渠道断面结构型式多样,用到的参考资料涉及范围广,因此．有必要对渠道水力断面公式在农业综合开发项目中的设计与应用进行归纳和探索。     

基于水文水动力模型的浦阳江流域洪水情景模拟

浦阳江流域地形复杂,包括山丘、盆地和平原.中游诸暨盆地是人口主要聚集地,受上游山区洪水和下游钱塘江潮位顶托影响,洪涝灾害形势严峻.为解决上述问题,本文对流域上游山区采用新安江水文模型模拟降雨径流过程,对下游盆地区采用IFMS一、二维水动力模型模拟水流运动,并以水文模型的计算结果作为水动力模型的边界条件进行水文水动力模型...     

Integrated hydrologic-economic modelling for analyzing water acquisition strategies in the Murray River Basin

We describe a coupled hydrologic-economic spreadsheet model for the Murray-Darling Basin that allows analyses of water allocation and use by different sectors including agriculture and environment under alternative policy scenarios. The model is a simple, lumped optimisation model which includes partitioning of rainfall into runoff and evapotranspiration, a reach by reach water balance of the river system, irrigation demand and revenue generation. Groundwater is not considered because groundwater use is a small part of the overall water use. The model is used to optimize profit, diversions and flows subject to hydrological and economic constraints determined by the policy scenario.We use the model to examine approaches of acquiring water for reallocation to the environment, and their impacts on irrigation water use and regional income from agriculture. We show that the optimal approach for acquisition depends on: economic factors, including the cost of water and the profits generated by its use; institutional factors, such as restrictions to trade between regions; and, hydrological factors, particularly the connectivity of and losses within the river network.The volume of water to be acquired does not, in general, equal the volume to be allocated. For a downstream site, water must be acquired from upstream, and more water must be acquired than is to be allocated: the volume acquired is that to be allocated plus transmission losses between the locations of acquisition and allocation. For upstream sites, it is optimal to acquire some water from downstream, and less water must be acquired than is to be allocated: the volume acquired is that to be allocated, less the transmission losses no longer incurred between the locations of acquisition and allocation.The volumes of water that must be acquired to satisfy an allocation target and maintain flows in the river system are affected by restrictions on trade between sub-catchments.     

Assessing multi-criteria approaches with environmental, economic and social attributes, weights and procedures: A case study in the Pampas, Argentina

Soil erosion control is a major issue in agriculture. The no till system of soybean production has been widely adopted; however, soil erosion may increase due to pasture and forestry land convertion to cropland in the marginal Pampas, Argentina. The aim of this paper is to assess the conflicts and trade-off among environmental, economic and social interests by using three continuous multi-criteria approaches and a set of different weights. Different land uses, crops, pastures, forestry and soil and water conservation practices at the basin scale in the marginal Pampas were assessed. The basin (423 km²) was discretised into 176 sub-basins to focus the management strategy on 5th and 6th order streams. Minimum basic information was obtained using intensive field observations and satellite images. The basin hydrology, soil erosion, sediment delivery and vegetated filter strip models and GIS were used to quantify the technical coefficients. Thirteen decision factors and six criteria (peak run-off, annual erosion, sediment, investment, gross margin and employment) were used in the optimisation trials. Weighted goal programming, lexicographic goal programming, compromise programming and a sensitivity analysis of weights were performed. The results showed a high impact of soil and water management practices on the environmental factors and a strong conflict between environmental and economic interests. The three multi-criteria approaches also showed that it is possible to obtain a good level of goal achievement with different plans. These plans should include: soil conservation practices; crop rotation (of a 2:1 soybean-to-corn ratio); gully and channel erosion control; regulation ponds; and pasture and agro-forestry areas. This goal achievement is mainly limited by public and private investment. Sensitivity analysis of the decision-maker weights shows differences among the values achieved by the criteria and their trade-off. Thus, the weight value of each criterium should be supported by the negotiation-consensus process.     

Development of a pathogen transport model for Irish catchments using SWAT

SWAT (Soil and Water Assessment Tool) represents a dynamic catchment modelling application that can be applied to any river basin and used to quantify the impact of land management practices on water quality over a continuous period. The objective of this study is to apply the Soil and Water Assessment Tool (SWAT) to model pathogen transport, simulate management practices affecting water quality and predict pathogen loads in Irish catchments. Based on input data regarding agricultural practice, demographics and hydrological parameters for the river Fergus catchment, SWAT was run to predict concentrations of Escherichia coli. Hydrometric validation results display a very good linear relationship between observed and predicted data (Coefficient of determination R² = 0.83, Nash-Sutcliffe efficiency E = 0.78) and indicate satisfactory simulation of hydrologic processes within the catchment. To date, pathogen predictions have proved variable between observed and simulated figures. Based on recommended values for the quantification of catchment modelling accuracy, predictions for E. coli can be described as acceptable and satisfactory with R² = 0.68 and E = 0.59. Extensive monitoring is required for such simulations and the current study represents partial validation. Results suggest that although the capabilities exist to simulate pathogen transport in catchments, the capacity to accurately account for all factors that can contribute to water degradation is uncertain. The sensitivity analysis identified the bacteria partition coefficient (BACTKDDB) as the most important input parameter. In addition it reveals areas where further research is required, particularly in assessing the initial concentration of E. coli in human/animal waste. The developed model provides a tool capable of protecting water sources and human health from waterborne pathogens.     

Agriculture in South Asia and its implications on downstream health and sustainability: A review

Agriculture, a century old practice, has rarely been questioned as it is a necessity for feeding the world's population. With the increase in food requirement, the sustainability of upland agriculture has posed threats to downstream and coastal areas of river basins. In South Asia, the coastal population depends on the lower part of the river basin for their livelihood such as agriculture and aquaculture. There have been numerous occasions where downstream areas have suffered as a consequence of ad hoc agricultural development activities upstream. Problems encountered in the downstream coastal areas include river desiccation, groundwater depletion, water pollution and sedimentation, salinization and salt water intrusion, soil erosion and nutrient depletion, and dynamic changes in the coastal wetland systems. The objective of this paper is to evaluate current agricultural practices, existing problems, and their implications downstream. This would facilitate the adoption of the river basin approach in managing water resources focusing on the South Asian region.     

An integrated hydro-economic modelling framework to evaluate water allocation strategies II: Scenario assessment

In this paper the results of an assessment of the hydrological and economic implications of reallocating water in the Musi sub-basin, a catchment within the Krishna Basin in India, are reported. Policy makers identified a number of different but plausible scenarios that could apply in the sub-basin, involving; supplying additional urban demand from agricultural allocations of water, implementing a number of demand management strategies, changing the timing of releases for hydropower generation, changing the crops grown under irrigation, reducing existing stream flows and allowing for more environmental flows. The framework chosen to undertake this assessment was a simulation model that measures and compares the economic values of water allocation scenarios determined from a water allocation model that accounts for supplies of groundwater and surface water across a number of regions and over a variety of uses. Policy makers are provided with the range of measures on the security of the supply of water and the social costs and benefits of reallocating water between sectors and across regions within the sub-basin. Taking water from agriculture to supply urban users has a greater impact on irrigation supplies during dry years. It was also found that changing the allocation of water between sectors, by taking it away from agriculture had a large positive economic impact on the urban sector. Yet the costs involved in undertaking such a strategy results in a significant loss in the net present value of the scheme. Stream flow reductions, if significantly large (at around 20%), were found to have a large physical and economic impact on the agricultural sector. Implementing water saving strategies in Hyderabad was found to be more cost effective than taking water from agriculture, if rainwater tanks are used to achieve this. Changing the timing of hydropower flows resulted in best meeting of irrigation demand in NSLC and NSRC. Under this scenario, the crops grown under irrigation were found to have a significant economic impact on the sub-basin, but not as large as farmers undertaking crop diversification strategies, ones which result in farmers growing less rice. The security of supplying water to different agricultural zones has significantly improved under this scenario. Finally, releasing water for environmental purposes was found to have only a minor impact on the agricultural sector.