Global irrigation water demand: Variability and uncertainties arising from agricultural and climate data sets

Agricultural water use accounts for around 70% of the total water that is withdrawn from surface water and groundwater. We use a new, gridded, global-scale water balance model to estimate interannual variability in global irrigation water demand arising from climate data sets and uncertainties arising from agricultural and climate data sets. We used contemporary maps of irrigation and crop distribution, and so do not account for variability or trends in irrigation area or cropping. We used two different global maps of irrigation and two different reconstructions of daily weather 1963–2002. Simulated global irrigation water demand varied by ∼30%, depending on irrigation map or weather data. The combined effect of irrigation map and weather data generated a global irrigation water use range of 2200 to 3800 km3 a−1. Weather driven variability in global irrigation was generally less than ±300 km3 a−1, globally (\u3c∼10%), but could be as large as ±70% at the national scale

The role of tropical forests in supporting biodiversity and hydrological integrity: a synoptic overview

Conservation of high-biodiversity tropical forests is sometimes justified on the basis of assumed hydrological benefits - in particular, the reduction of flooding hazards for downstream floodplain populations. However, the"far-field"link between deforestation and distant flooding has been difficult to demonstrate empirically. This simulation study assesses the relationship between forest cover and hydrology for all river basins intersecting the world's tropical forest biomes. The study develops a consistent set of pan-tropical land cover maps gridded at one-half degree latitude and longitude. It integrates these data with existing global biogeophysical data. The study applies the Water Balance Model - a coarse-scale process-based hydrological model - to assess the impact of land cover changes on runoff. It quantifies the impacts of forest conversion on biodiversity and hydrology for two scenarios - historical forest conversion and the potential future conversion of the most threatened remaining tropical forests. A worst-case scenario of complete conversion of the most threatened of the remaining forested areas would mean the loss of another three million km2 of tropical forests. Increased annual yield from the conversion of threatened tropical forests would be less than 5 percent of contemporary yield in aggregate. However, about 100 million people - 80 million of them in floodplains - would experience increases of more than 25 percent in annual water flows. This might be associated with commensurate increases in peak flows, though further analysis would be necessary to gauge the impact on flooding. The study highlights basins in Southeast Asia, southern China, and Latin America that warrant further study.Wetlands,Forestry,Climate Change,Drylands&Desertification,Earth Sciences&GIS

The significance of local water resources captured in small reservoirs for crop production – A global-scale analysis

Rainwater harvesting, broadly defined as the collection and storage of surface runoff, has a long history in supplying water for agricultural purposes. Despite its significance, rainwater harvesting in small reservoirs has previously been overlooked in large-scale assessments of agricultural water supply and demand. We used a macroscale hydrological model, observed climate data and other physical datasets to explore the potential role of small, localized rainwater harvesting systems in supplying water for irrigated areas. We first estimated the potential contribution of local water harvesting to supply currently irrigated areas. We then explored the potential of supplemental irrigation applied to all cropland areas to increase crop evapotranspiration (or green water flow), using locally stored surface runoff in small reservoirs for different scenarios of installed reservoir capacity. The estimated increase in green water flow varied between 623 and 1122 km3 a1 . We assessed the implications of this increase in green water flows for cereal production by assuming a constant crop water productivity in areas where current levels of crop yield are below global averages. Globally, the supplemental irrigation of existing cropland areas could increase cereal production by 35% for a medium variant of reservoir capacity, with large potential increases in Africa and Asia. As small reservoirs can significantly impact the hydrological regime of river basins, we also assessed the impacts of small reservoirs on downstream river flow and quantified evaporation losses from small reservoirs

Changes in moisture and energy fluxes due to agricultural land use and irrigation in the Indian Monsoon Belt

We present a conceptual synthesis of the impact that agricultural activity in India can have on land-atmosphere interactions through irrigation. We illustrate a “bottom up” approach to evaluate the effects of land use change on both physical processes and human vulnerability. We compared vapor fluxes (estimated evaporation and transpiration) from a pre-agricultural and a contemporary land cover and found that mean annual vapor fluxes have increased by 17% (340 km3) with a 7% increase (117 km3) in the wet season and a 55% increase (223 km3) in the dry season. Two thirds of this increase was attributed to irrigation, with groundwater-based irrigation contributing 14% and 35% of the vapor fluxes in the wet and dry seasons, respectively. The area averaged change in latent heat flux across India was estimated to be 9 Wm−2. The largest increases occurred where both cropland and irrigated lands were the predominant contemporary land uses

Probable maximum precipitation estimation using multifractals: Application in the eastern united states

ABSTRACT Probable maximum precipitation (PMP) is the conceptual construct that defines the magnitude of extreme storms used in the design of dams and reservoirs. In this study, the value and utility of applying multifractal analysis techniques to systematically calculate physically meaningful estimates of maximum precipitation from observations in the eastern United States is assessed. The multifractal approach is advantageous because it provides a formal framework to infer the magnitude of extreme events independent of empirical adjustments, which is called the fractal maximum precipitation (FMP), as well as an objective estimate of the associated risk. Specifically, multifractal (multiscaling) behavior of maximum accumulated precipitation at daily (327 rain gauges) and monthly (1400 rain gauges) timescales, as well as maximum accumulated 6-hourly precipitable water fluxes for the period from 1950 to 1997 were characterized. Return periods for the 3-day FMP estimates in this study ranged from 5300 to 6200 yr. The multifractal parameters were used to infer the magnitude of extreme precipitation consistent with engineering design criterion (e.g., return periods of 10 6 yr), the design probable maximum precipitation (DPMP). The FMP and DPMP were compared against PMP estimates for small dams in Pennsylvania using the standard methodology in engineering practice (e.g., National Weather Service Hydrometeorological Reports 51 and 52). The FMP estimates were usually, but not always, found to be lower than the standard PMP (FMP/PMP ratios ranged from 0.5 to 1.0). Furthermore, a high degree of spatial variability in these ratios points to the importance of orographic effects locally, and the need for place-based FMP estimates. DMP/PMP ratios were usually greater than one (0.96 to 2.0), thus suggesting that DPMP estimates can provide a bound of known risk to the standard PMP

Integrated Analysis of the Value of Wetland Services in Coastal Adaptation; Methodology and Case Study of Hampton-Seabrook Estuary, New Hampshire

The present impacts from coastal storms and high tides grow significantly over time due to SLR even over the relatively short period to 2060. Hydrodynamic model simulations of storm surge with and without sea level rise scenarios show that although flooding and inundation increases with increasing subtidal forcing and higher sea level, dissipation of the tide and storm surge in the estuary channel somewhat limits the maximum inundation that might otherwise be expected in the back marsh areas. The estuary is dominated by high marsh, which lies high in the intertidal zone and by 2060 it will convert to mostly low marsh unless it can build very rapidly (greater than 5 mm/year). The marsh supports fisheries and many charismatic birds, some marsh dependent, and provides a culturally significant view-scape across the estuary. The Sea Level Affecting Marsh Model (SLAMM) was used to predict habitat changes due to 0.73 m SLR by 2060 under different accretion rates and levels of protection for developed areas that became intertidal. Although the relative amounts of high marsh and low marsh varied dramatically, the overall marsh area remained within 5% of the current levels and mostly increased if marsh accretion rates exceeded 2 mm/year. Limited areas of intertidal flats supporting shellfish exist in present day, but in the near future culturally important recreational shellfish areas will convert to open water. However, areas that are currently low marsh will drown and may provide future shellfish areas. The open water harbor is important for boating, access to coastal waters and recreational fishing. Currently, the open water area is small, but may double in size by 2060 and the greater tides relative to the marsh elevation will create a different feel for the estuarine landscape in the future because high tides will regularly cover larger areas of the marsh with seawater. Outside of the estuary on the oceanfront, beaches and dunes support tourism and intensive recreational use as well as federally protected nesting shorebirds (piping plover, least tern). Most of the outer beach is exposed to Gulf of Maine waters. Where there are existing floodwalls, rising sea levels will worsen the storm danger and damage to the integrity of the walls. Unless walls are raised, storms will also transport massive amounts of beach sediments over the walls and across the barrier system. Beaches will have less width and steep ramping to the walls will severely decrease the value of the beach for tourism. In areas with dune systems, very little change is predicted for this area because the dynamic equilibria of the dune-beach system will allow the beach to build in elevation as sea level rises and wind-driven dune building will continue. Bedrock outcrops (at Plaice Cove, Great Boars Head and the inlet) help reduce landward erosion. The socio-economic impacts result in more people flooded as sea level rises, particularly of socially vulnerable populations, and more anchor institutions flooded. Residents presently living in the most socially vulnerable census blocks were 8.6 times more likely to be located in the flood zone, compared to those living in blocks with low social vulnerability. Under climate change,census blocks with high percentages of the population living in poverty were 17.7 times more likely to be located in the flood zone. This analysis more likely reflects the winter/spring population than the summer population. The estimated annual expected value damages in the present are approximately $0.90 M. In 2060 with SLR they are$4.8 M. Using a 7 % discount rate, the present expected value of these damages between 2018 and 2060 is approximately $27 M. There are many sources of possible error in this value due to missing data, and not including damages to infrastructure, human mortality and morbidity, lost business (particularly recreation), and other cascading and multiplier events. We also do not include the value of ecosystem services. The adaptation goal focused on protecting the socio-economic systems of the barrier beach areas. Engineering approaches that only use hard structures or grey solutions may weigh the communities down with severe debt, result in long term damage to the environment and degrade the charm and attractiveness of the area to tourists. On the other hand, allowing over-wash and marsh migration everywhere will reduce the number of people and tourists that benefit from the beaches and dunes, shellfish flats, marinas, fishing and marshes. Because marshes of limited area do not significantly decrease storm surge and there is limited wave activity on the western, inland side of the barrier beaches, the marshes may not directly contribute to reducing the flooding on the western side of the barrier beaches. Regional solutions such as building a berm or a floodwall (smaller footprint limits direct marsh losses) to limit land loss will prevent marsh migration. Flood protection berms to protect all residential development bordering the estuary will result in significant marsh loss. Individual site flood management actions such elevating buildings must be employed there. The most expensive adaptations are needed on the coastal side where the beach-dune system has been replaced by an armored shoreline (seawalls) designed for pedestrians and automobiles, but not beach goers. These walls need to be fortified; their expansion opens an opportunity to provide alternate transportation pathways that are safe (bike lane), green space, and a more attractive promenade (increasing ecosystem/cultural services for residents and visitors). The beaches need to be nourished to provide sandy areas at high tide (especially in the northern areas) to better support the tourism industry. The two oceanfront sections without walls or dune systems were especially vulnerable; these could benefit from green adaptation solutions that construct and maintain sacrificial dunes at relatively low cost. Residential areas landward of existing dune fields were deemed the best protected and only required low cost adaptation decisions (e.g., building sand barriers at beach access cuts and maintaining dune health). Heavily used roads that cross marshes on causeways will need to be raised. Although more expensive, roadways elevated above the marsh surface will reduce impacts from direct filling and provide better tidal exchange. Thus throughout the HSE, there are limited reasonable green options for coastal flood management here. The present value adaptation costs in 2018 including capital and maintenance costs discounted at 7$149 M. This adaptation cost is more than the previously estimated damage avoided cost or benefit of $27 M. Because, as noted earlier, this benefit estimate is significantly underestimated due to data and methodological limitations, we cannot really state this project is not cost-effective; it actually may be cost effective. A lower discount rate would also increase it cost-effectiveness. Adaptation would mitigate some of the direct impacts to social vulnerable populations, but in some areas would require towns investing in the protection of their individual residents instead of being part of a possibly less costly regional solution. The adaptation plan could provide important public health benefits through the addition of the green elevated walkway (in place of current parkingspaces) along the floodwall. We met with several local non-governmental (NG) and mixed governmental and NG organizations over the grant lifetime. They generally support our findings. One possible troubling possibility is that 75As described above, the marshes themselves are not major contributors to present and future flood protection in the area. They are, of course, valuable for other reasons. Examples include habitat, runoff treatment, recreation, tourism, and carbon storage. An estimate of the annual values of these services in HSE are approximately$370 M under present and future SLR conditions. Thus, their preservation should be a priority

Level and source of supplemental selenium for beef steers

Selenium (Se) is deficient in many Arkansas soils; therefore, an experiment was conducted on steers to evaluate the effects of two supplemental Se sources on performance, blood metabolites, and immune function. Thirty Angus-crossbred steers were blocked by weight and assigned within block to one of 15 pens (two steers/pen). Pens were assigned randomly within blocks to one of three dietary treatments consisting of a corn-soybean meal supplement devoid of supplemental Se (negative control, NC) or corn-soybean meal supplements providing 1.7 mg supplemental Se/d as sodium selenite (inorganic Se, ISe) or as Se yeast (organic Se, OSe). Steers were offered fescue hay to allow for approximately 10% refusals, and 1.1 kg/d (as fed basis) of the appropriate grain supplement. Level and source of supplemental Se did not affect average daily gain for the 105-d trial. By d 42, steers fed both sources of supplemental Se had greater blood Se concentrations than those fed the NC. On d 63 and 84, blood Se concentrations differed among all dietary treatments (NC \u3c ISe \u3c OSe), and on d 105 steers fed both sources of supplemental Se had greater blood Se concentrations than NC. Antibody response to vaccination for bovine respiratory viruses, or in vitro lymphocyte blastogenesis did not differ among steers fed the different diets. Both sources of supplemental Se increased blood Se concentrations, the organic source more rapidly than the inorganic source; however, Se level and source had minimal effects on immune function of weaned beef steers