A Detailed Hydro-Economic Model for Assessing the Effects of Surface Water and Groundwater Policies: A Demonstration Model from Brazil

Policymakers, managers of water use associations, and many others in developing countries are considering policy actions that will directly or indirectly change the costs and availability of groundwater and surface water for agricultural users. While in many cases such actions may bring about welcomed increases in water use efficiency, little is known about the likely effects of changes in irrigation costs or water access on farmer behavior, or on farmer incomes in the short or long runs, and virtually nothing is known about the detailed immediate or knock-on effects on water resources that such policy actions might cause. This paper reports the preliminary results of research aiming to fill these large scientific gaps by developing a detailed hydrologic model and a detailed economic model of agriculture in the context of the Buriti Vermelho (BV) sub-catchment area of the São Francisco River Basin in Brazil. A spatially explicit, farm-level, positive mathematical programming model capable of accommodating a broad array of farm sizes and farm/farmer characteristics is being developed to predict the effects of alternative water policies and neighbors water use patterns on agricultural production. Special attention is given to precisely defining and estimating the distinct variable costs (including labor and electrical energy costs) and capital costs of surface water and groundwater, which are considered perfect substitutes for irrigation. Shadow values for non-marketed inputs (land, family labor, and water) are estimated in the first step of the modeling process. A high-resolution, spatially distributed hydrologic model (MOD-HMS) is being developed to simulate three-dimensional, variably-saturated subsurface flow and solute transport. Subsurface flow is simulated using the three-dimensional Richards equation while accounting for a) application of water at the surface, b) precipitation, c) soil evaporation and crop transpiration, and d) agricultural pumping. Demonstration versions of both models are presented and tested: the economic model assesses the effects of increasing water scarcity on cultivated area, crop mix, input mix and farm profits; the hydrologic model uses two irrigation water use scenarios to demonstrate the effects of each on surface water flows and storage, and on groundwater storage and well depth. The models are not currently linked, but a detailed plan to do so is presented and discussed. The paper concludes by discussing next steps in research and policy simulations.Resource /Energy Economics and Policy,

Coastal development and precipitation drive pathogen flow from land to sea: evidence from a Toxoplasma gondii and felid host system

Rapidly developing coastal regions face consequences of land use and climate change including flooding and increased sediment, nutrient, and chemical runoff, but these forces may also enhance pathogen runoff, which threatens human, animal, and ecosystem health. Using the zoonotic parasite Toxoplasma gondii in California, USA as a model for coastal pathogen pollution, we examine the spatial distribution of parasite runoff and the impacts of precipitation and development on projected pathogen delivery to the ocean. Oocysts, the extremely hardy free-living environmental stage of T. gondii shed in faeces of domestic and wild felids, are carried to the ocean by freshwater runoff. Linking spatial pathogen loading and transport models, we show that watersheds with the highest levels of oocyst runoff align closely with regions of increased sentinel marine mammal T. gondii infection. These watersheds are characterized by higher levels of coastal development and larger domestic cat populations. Increases in coastal development and precipitation independently raised oocyst delivery to the ocean (average increases of 44% and 79%, respectively), but dramatically increased parasite runoff when combined (175% average increase). Anthropogenic changes in landscapes and climate can accelerate runoff of diverse pathogens from terrestrial to aquatic environments, influencing transmission to people, domestic animals, and wildlife

Sustainable Eco-Systems under Land Retirement

This study uses five years of field data from the Land Retirement Demonstration Project located in western Fresno County of California to develop a comprehensive theoretical and numerical modeling framework to evaluate the specific site conditions required for a sustainable land retirement ecosystem outcome based on natural drainage. Using field data, principles of mass balance in a control volume, the HYDRUS-1D Software Package for simulating one-dimensional movement of water, heat, and multiple solutes in variably-saturated media, and PEST, a modelindependent parameter optimizer, the processes of soil water and solute movement in root zone and the deep vadose zone were investigated. The optimization of unsaturated soil hydraulic parameters and downward flux (natural drainage) from the control volume against observed vadose zone salinity levels and shallow groundwater levels yield difficult to obtain natural drainage rate as a function of water table height within the control volume. The results show that unsaturated soil hydraulic properties and the downward flux from the soil profile are the critical parameters. A ‘natural drainage approach’ to sustainable land management for drainage impaired land is proposed. With this approach it is feasible to design a sustainable land use regimen for drainage impaired lands in general and retired lands in particular.Further analysis of data on the evolution of vadose zone salinity and perched water levels also show that effective unsaturated soil hydraulic property and the "natural drainage rate" change with average soil water salinity. The results show that at the same pressure head, soil water content is less with higher soil water salinity as compared to lower soil water salinity. It is thus concluded that the use of soil water salinity invariant soil water hydraulic parameters in numerical modeling can seriously compromise prediction, especially for a variable soil water salinity environment

Crop Residue Biomass Effects on Agricultural Runoff

High residue loads associated with conservation tillage and cover cropping may impede water flow in furrow irrigation and thus decrease the efficiency of water delivery and runoff water quality. In this study, the biomass residue effects on infiltration, runoff, and export of total suspended solids (TSS), dissolved organic carbon (DOC), sediment-associated carbon (TSS-C), and other undesirable constituents such as phosphate (soluble P), nitrate (), and ammonium () in runoff water from a furrow-irrigated field were studied. Furrow irrigation experiments were conducted in 91 and 274 m long fields, in which the amount of residue in the furrows varied among four treatments. The biomass residue in the furrows increased infiltration, and this affected total load of DOC, TSS, and TSS-C. Net storage of DOC took place in the long but not in the short field because most of the applied water ran off in the short field. Increasing field length decreased TSS and TSS-C losses. Total load of , , and soluble P decreased with increasing distance from the inflow due to infiltration. The concentration and load of P increased with increasing residue biomass in furrows, but no particular trend was observed for and . Overall, the constituents in the runoff decreased with increasing surface cover and field length

Effects of field length and management practices on dissolved organic carbon export in furrow irrigation

Farming practices, including tillage, cover cropping and residue management can have profound effects on the efficiency of irrigation practices. The effects of three field management practices (FMPs) standard tillage and winter-fallow (ST), standard tillage and winter-cover crop (STCC), and no-till and winter-fallow (NT) and two field lengths (122 and 366 m) on runoff and export of dissolved organic carbon (DOC) were investigated in a furrow-irrigated cropping system over two years. The residue cover was 40, 32 and 11% in 2007, and 58, 61 and 11% in 2008 for STCC, NT and ST, respectively. Furrow irrigation experiments were conducted prior to crop planting following the cover crop. The inflow was kept constant across all treatments, and infiltration and runoff were estimated using a volume balance model (VBM). The DOC concentration tended to increase with increasing field length, but did not differ among the FMPs. A threefold increase in field length increased infiltration by 40%, and decreased runoff by 60-90% and DOC export by 65-83%. In both years, infiltration was highest in STCC. In NT, infiltration was lowest in 2007, which was likely due to soil sealing, and intermediate among the three FMPs in 2008 perhaps due to the increase in residue cover in the second year. The DOC budget analysis showed that fields and FMPs acted as DOC sinks exporting less DOC than was applied in the irrigation water. The results suggest that longer furrows and STCC were greater DOC sinks compared to ST and shorter field practices. The VBM, as applied in this study to estimate infiltration and runoff, could be used to predict optimal field length to minimize runoff and promote DOC adsorption to soil within the constraints of water quality and availability and soil conditions.Furrow irrigation Dissolved organic carbon No till Field length Cover crop Volume balance

Water sensors with cellular system eliminate tail water drainage in alfalfa irrigation

Alfalfa is the largest consumer of water among all crops in California. It is generally flood-irrigated, so any system that decreases runoff can improve irrigation efficiency and conserve water. To more accurately manage the water flow at the tail (bottom) end of the field in surface-irrigated alfalfa crops, we developed a system that consists of wetting-front sensors, a cellular communication system and a water advance model. This system detects the wetting front, determines its advance rate and generates a cell-phone alert to the irrigator when the water supply needs to be cut off, so that tail water drainage is minimized. To test its feasibility, we conducted field tests during the 2008 and 2009 alfalfa growing seasons. The field experiments successfully validated the methodology, producing zero tail water drainage

Water sensors with cellular system eliminate tail water drainage in alfalfa irrigation

Alfalfa is the largest consumer of water among all crops in California. It is generally flood-irrigated, so any system that decreases runoff can improve irrigation efficiency and conserve water. To more accurately manage the water flow at the tail (bottom) end of the field in surface-irrigated alfalfa crops, we developed a system that consists of wetting-front sensors, a cellular communication system and a water advance model. This system detects the wetting front, determines its advance rate and generates a cell-phone alert to the irrigator when the water supply needs to be cut off, so that tail water drainage is minimized. To test its feasibility, we conducted field tests during the 2008 and 2009 alfalfa growing seasons. The field experiments successfully validated the methodology, producing zero tail water drainage