Dual water-electricity cooperation improves economic benefits and water equality in the Lancang-Mekong River Basin.

Transboundary river cooperation provides an effective pathway to maintain regional security and sustainable development; however, its implementation is a pressing and prominent concern due to lack of appropriate compensation measures and effective incentive strategies. Here we develop a dual water-electricity cooperation (DWEC) framework that combines water and electricity trading to meet the often-conflicting demands of participating countries. The results from the Lancang-Mekong River Basin reveal that substantial benefits in both economic and social aspects can be achieved through coupling regional water and electricity trades. Economic benefits can be obtained by expanding cooperation space and thereby greatly improving the willingness of countries to participate in basin-wide cooperation. Electricity trading plays a key role in loss compensation for water exporters, ensuring no loss for any party and maximizing basin-wide benefits. Furthermore, the DWEC improves regional water use equality, especially in water shortage periods when there is severe competition among water users. The proposed cooperation framework provides a viable way to implement cooperation in transboundary river basins.

Seasonal Risk Assessment of Water-Electricity Nexus Systems under Water Consumption Policy Constraint.

Previous studies have estimated power plant cooling water consumption based on the long-term average cooling water consumption intensity (WI: water consumption per unit of electricity generation) at an annual scale. However, the impacts of the seasonality of WI and streamflow on electricity generation are less well understood. In this study, a risk assessment method is developed to explore the seasonal risk of water-electricity nexus based on the Integrated Environmental Control Model, which can simulate variable WIs in response to daily weather conditions and avoid underestimation in WIs as well as nexus risk during dry seasons. Three indicators, reliability, maximum time to recovery, and total power generation loss, are proposed to quantify the seasonal nexus risk under water consumption policy constraint represented by the allowed maximum percentage of water consumption to streamflow. The applications of the method in two representative watersheds demonstrate that the nexus risk is highly seasonal and is greatly impacted by the seasonal variability of streamflow rather than annual average water resources conditions on which most previous studies are based. The nexus is found more risky in the watershed with almost double mean annual streamflow and greater streamflow variability, compared with the watershed with less streamflow variability.

Is water shortage risk decreased at the expense of deteriorating water quality in a large water supply reservoir?

Reservoir operations affect both the quantity and quality of stored and discharged water. Hedging rules (HRs) are commonly used in water supply reservoir operations to ration water delivery and decrease water shortage risk. However, the increased carryover storage with hedging may aggravate reservoir eutrophication through complex effects on hydrodynamic, temperature, light, nutrient, and sediment conditions. The influencing mechanisms are unclear and require further investigation. This study applies a mathematical modeling approach to comparing the effects of standard operation policy (SOP) and HR, discussing the processes and driving factors, and exploring the relationship between water shortage and water quality indicators. We simulate reservoir operation by SOP and optimize HR to generate water supply schedules, and run a quasi-3D water quality model to simulate reservoir hydrodynamic conditions, nutrient cycles, water-sediment exchanges, and algal dynamics under various water supply schedules. The Danjiangkou Reservoir, the water source for China's South-North Water Transfer Project, is used as a case study. The HR for this reservoir decreases its water shortage risk from 22% under SOP to 8%. Modeling results find that the HR increases sediment phosphorus (P) release by 285.3 tons (5.7%) annually as a consequence of extended reservoir submerged area and aggravated hypolimnetic hypoxia. Increased P release can support algal growth, but this effect is set off by the enhancement of light limiting effect caused by higher storages under HR, consequently decreasing the annual mean chlorophyll a concentration in the deep reservoir by 18%. The HR also improves the horizontal mixing of water by changing the hydraulic retention time and flow velocity field, which mitigates algal bloom risks in the surrounding shallow-water zones but deteriorates water quality of the release to downstream. The water quality analysis offers implications for reservoir managers to coordinate their efforts in mitigating risks of water shortage and water quality degradation.

The Interplay Between Bioenergy Grass Production and Water Resources in the United States of America.

We apply a land surface model to evaluate the interplay between potential bioenergy grass (Miscanthus, Cave-in-Rock, and Alamo) production, water quantity, and nitrogen leaching (NL) in the Central and Eastern U.S. Water use intensity tends to be lower where grass yields are modeled to be high, for example in the Midwest for Miscanthus and Cave-in-Rock and the upper southeastern U.S. for Alamo. However, most of these regions are already occupied by crops and forests and substitution of these biome types for ethanol production implies trade-offs. In general, growing Miscanthus consumes more water, Alamo consumes less water, and Cave-in-Rock consumes approximately the same amount of water as existing vegetation. Bioenergy grasses can maintain high productivity over time, even in water limited regions, because their roots can grow deeper and extract the water from the deep, moist soil layers. However, this may not hold where there are frequent and intense drought events, particularly in regions with shallow soil depths. One advantage of bioenergy grasses is that they mitigate nitrogen leaching relative to row crops and herbaceous plants when grown without applying N fertilizer; and bioenergy grasses, especially Miscanthus, generally require less N fertilizer application than row crops and herbaceous plants.

Carbon consequences and agricultural implications of growing biofuel crops on marginal agricultural lands in China.

Using marginal agricultural lands to grow energy crops for biofuel feedstocks is a promising option to meet the biofuel needs in populous China without causing further food shortages or environmental problems. Here we quantify the effects of growing switchgrass and Miscanthus on Chinese marginal agricultural lands on biomass production and carbon emissions with a global-scale biogeochemical model. We find that the national net primary production (NPP) of these two biofuel crops are 622 and 1546 g C m(-2) yr(-1), respectively, whereas the NPP of food crops is about 600 g C m(-2) yr(-1) in China. The net carbon sink over the 47 Mha of marginal agricultural lands across China is 2.1 Tg C yr(-1) for switchgrass and 5.0 Tg C yr(-1) for Miscanthus. Soil organic carbon is estimated to be 10 kg C m(-2) in both biofuel ecosystems, which is equal to the soil carbon levels of grasslands in China. In order to reach the goal of 12.5 billion liters of bioethanol in 2020 using crop biomass as biofuel feedstocks, 7.9-8.0 Mha corn grain, 4.3-6.1 Mha switchgrass, or 1.4-2.0 Mha Miscanthus will be needed. Miscanthus has tremendous potential to meet future biofuel needs, and to benefit CO(2) mitigation in China.

Land availability for biofuel production.

Marginal agricultural land is estimated for biofuel production in Africa, China, Europe, India, South America, and the continental United States, which have major agricultural production capacities. These countries/regions can have 320-702 million hectares of land available if only abandoned and degraded cropland and mixed crop and vegetation land, which are usually of low quality, are accounted. If grassland, savanna, and shrubland with marginal productivity are considered for planting low-input high-diversity (LIHD) mixtures of native perennials as energy crops, the total land availability can increase from 1107-1411 million hectares, depending on if the pasture land is discounted. Planting the second generation of biofuel feedstocks on abandoned and degraded cropland and LIHD perennials on grassland with marginal productivity may fulfill 26-55% of the current world liquid fuel consumption, without affecting the use of land with regular productivity for conventional crops and without affecting the current pasture land. Under the various land use scenarios, Africa may have more than one-third, and Africa and Brazil, together, may have more than half of the total land available for biofuel production. These estimations are based on physical conditions such as soil productivity, land slope, and climate.

Modeling Miscanthus in the soil and water assessment tool (SWAT) to simulate its water quality effects as a bioenergy crop.

There is increasing interest in perennial grasses as a renewable source of bioenergy and feedstock for second-generation cellulosic biofuels. The primary objective of this study is to estimate the potential effects on riverine nitrate load of cultivating Miscanthus x giganteus in place of conventional crops. In this study, the Soil and Water Assessment Tool (SWAT) is used to model miscanthus growth and streamwater quality in the Salt Creek watershed in Illinois. SWAT has a built-in crop growth component, but, as miscanthus is relatively new as a potentially commercial crop, data on the SWAT crop growth parameters for the crop are lacking. This leads to the second objective of this study, which is to estimate those parameters to facilitate the modeling of miscanthus in SWAT. Results show a decrease in nitrate load that depends on the percent land use change to miscanthus and the amount of nitrogen fertilizer applied to the miscanthus. Specifically, assuming a nitrogen fertilization rate for miscanthus of 90 kg-N/ha, a 10%, 25%, and 50% land use change to miscanthus will lead to decreases in nitrate load of about 6.4%, 16.5%, and 29.6% at the watershed outlet, respectively. Likewise, nitrate load may be reduced by lowering the fertilizer application rate, but not proportionately. When fertilization drops from 90 to 30 kg-N/ha the difference in nitrate load decrease is less than 1% when 10% of the watershed is miscanthus and less than 6% when 50% of the watershed is miscanthus. It is also found that the nitrate load decrease from converting less than half the watershed to miscanthus from corn and soybean in 1:1 rotation surpasses that from converting the whole watershed to just soybean.

Water stress, water transfer and social equity in Northern China--implications for policy reforms.

Water stress in Northern China is characterized with major, inefficient irrigation water use and rapidly growing non-agricultural water demands, as well as limited water quantity and declining water quality. Water use in the region is undergoing transfer from agricultural to municipal and industrial sectors. Currently, part of the economic loss and environmental damage due to water stress can be considered as a consequence of water transfer failures, including the current transfers, which hurt farmers' livelihood and income, and the needed transfers, which industry and cities have been waiting for but have not received. This paper starts with a discussion of the causes of water stress in Northern China, which is fundamental to understand the necessity and complexity of agricultural water transfers. Following that, it reviews water transfers in Northern China as a cause for concern over the social stability, economy and environment of the region. Based on an integrated analysis of economic, environmental, fiscal and social implications, this paper begins by identifying critical barriers to smooth water redistribution; and ends with implications for policy reforms, ensuring that farmers can and will save water. It is concluded that the decisions of water reallocation under water stress should be shared by communities at all levels, from the local to the national, to ensure equal access of water, especially the availability of the basic water need for all groups.