Simulating the Impacts of Land-Use Land-Cover Changes on Cropland Carbon Fluxes in the Midwest of the United States

Understanding the major drivers of the cropland carbon fluxes is important for carbon management and greenhouse gas mitigation in agriculture. Past studies found that agricultural land-use and land-cover (LULC) changes, such as changes in cropland production technologies, tillage practices, and planted crop species, could have large impacts on carbon fluxes. However, the impacts remain highly uncertain at regional to global scales. Satellite remote sensing is commonly used to create products with geospatial information on LULC changes. This geospatial information can be integrated into biogeochemical models to simulate the spatial and temporal patterns of carbon fluxes. We used the General Ensemble Biogeochemical Modeling System (GEMS) to study LULC change impacts on cropland carbon fluxes in the Midwest USA. First we evaluated the impacts of LULC change on cropland net primary production (NPP) estimates. We found out the high spatial variability of cropland NPP across the study region was strongly related to the changes in crop species. Ignoring information about crop species distributions could introduce large biases into NPP estimates. We then investigated whether the characteristics of LULC change could impact the uncertainties of carbon flux estimates (i.e., NPP, net ecosystem production (NEP) and soil organic carbon (SOC)) using GEMS and two other models. The uncertainties of all three flux estimates were spatial autocorrelated. Land cover characteristics, such as cropland percentage, crop richness, and land cover diversity all showed statistically significant relationships with the uncertainties of NPP and NEP, but not with the uncertainties of SOC changes. The impacts of LULC change on SOC changes were further studied with historical LULC data from 1980 to 2012 using GEMS simulations. The results showed that cropland production increase over time from technology improvements had the largest impacts on cropland SOC change, followed by expansion of conservation tillage. This study advanced the scientific knowledge of cropland carbon fluxes and the impacts of various management practices over an agricultural area. The findings could help future carbon cycle studies to generate more accurate estimates on spatial and temporal changes of carbon fluxes

Quantifying future water resources availability and agricultural productivity in agro-urban river basins

Includes bibliographical references.2022 Fall.Climate change can have an adverse effect on agricultural productivity and water availability in semi-arid regions, as decreases in surface water availability can lead to groundwater depletion and resultant losses in crop yield due to reduced water for irrigation. Competition between urban and agricultural areas intensifies groundwater exploitation as surface water rights are sold to growing municipalities. These inter-relationships necessitate an integrated management approach for surface water, groundwater, and crop yield as a holistic system. This dissertation provides a novel integrated hydrologic modeling approach to quantify future water resources and agricultural productivity in agro-urban river basins, particularly in arid and semi-arid regions where surface water and groundwater are managed conjunctively to sustain urban areas and food production capacity. This is accomplished by i) developing an integrated hydrologic modeling code that accounts for groundwater and surface water processes and exchanges in large regional-scale managed river basins, and demonstrating its use and performance in the economically diverse South Platte River Basin (SPRB), a 72,000 km2 river basin located primarily in the state of Colorado, USA; ii) using the model to understand possible future impacts imposed by climate variation on water resources (surface water and groundwater) and agricultural productivity; and iii) quantifying the combination impacts of agriculture-to-urban water trading and climate change on groundwater resources within the basin. This dissertation presents an updated version of SWAT-MODFLOW that allows application to large agro-urban river basins in semi-arid regions. SWAT provides land surface hydrologic and crop yield modeling, whereas MODFLOW provides subsurface hydrologic modeling. Specific code changes include linkage between MODFLOW pumping cells and SWAT HRUs for groundwater irrigation and joint groundwater and surface water irrigation routines. This conjunctive use, basin-scale long-term water resources, and crop yield modeling tool can be used to assess future water and agricultural management for large river basins across the world. The updated modeling code is applied to the South Platte River Basin, with model results tested against streamflow, groundwater head, and crop yield throughout the basin. To assess the climate change impacts on water resources and agricultural productivity, the coupled SWAT-MODFLOW modeling code is forced with five different CMIP5 climate models downscaled by Multivariate Adaptive Constructed Analogs (MACA), each for two climate scenarios, RCP4.5, and RCP8.5, for 1980-2100. In all climate models and emission scenarios, an increase of 3 to 5 °C in annual average temperature is projected by the end of the 21st century, whereas variation in projected precipitation depends on topography and distance from the mountains. Based on the results of this study, the worst-case climate model in the basin is IPSL-CM5A-MR-8.5. Under this climate scenario, for a 1 °C increase in temperature and the 1.3% reduction in annual precipitation, the basin will experience an 8.5% decrease in stream discharge, 2-5% decline in groundwater storage, and 11% reduction in crop yield. In recent decades, there has been a growing realization that developing additional water supplies to address new demands is not feasible. Instead, managing existing water supplies through reallocations is necessary to tackle water scarcity and climate change. However, third-party effects associated to water transfers has limited the growing water market. This study also quantifies the combination impacts of agriculture-to-urban water trading (widely known as 'buy and dry') and climate change on groundwater availability in semi-arid river basins through the end of 21st century, as groundwater pumping increases to satisfy irrigation water lost to the urban sector. For this analysis, we use the hydrological modeling tool SWAT-MODFLOW, forced by projected water trading amounts and two downscaled GCM climate models, each for two emission scenarios, RCP4.5 and 8.5. According to the results of this study, agriculture-to-urban water trading imposes an additional basin-wide 2% reduction in groundwater storage, as compared to changes due to climate. However, groundwater storage changes for local subbasins can be up to 8% and 10% through the mid-century and end of the century, respectively

Simulating the effects of management practices on cropland soilorganic carbon changes in the Temperate Prairies Ecoregion of theUnited States from 1980 to 2012

Understanding the effects of management practices on soil organic carbon (SOC) is important for design-ing effective policies to mitigate greenhouse gas emissions in agriculture. In the Midwest United States,management practices in the croplands have been improved to increase crop production and reduce SOCloss since the 1980s. Many studies of SOC dynamics in croplands have been performed to understandthe effects of management, but the results are still not conclusive. This study quantified SOC dynam-ics in the Midwest croplands from 1980 to 2012 with the General Ensemble Biogeochemical ModellingSystem (GEMS) and available management data. Our results showed that the total SOC in the croplandsdecreased from 1190 Tg C in 1980 to 1107 TgC in 1995, and then increased to 1176 TgC in 2012. Contin-uous cropping and intensive tillage may have driven SOC loss in the early period. The increase of cropproduction and adoption of conservation tillage increased the total SOC so that the decrease in the totalSOC stock after 32 years was only 1%. The small change in average SOC did not reflect the large spatialvariations of SOC change in the region. Major SOC losses occurred in the north and south of the region,where SOC baseline values were high and cropland production was low. The SOC gains took place in thecentral part of the region where SOC baseline values were moderate and cropland production was higherthan the other areas. We simulated multiple land-use land-cover (LULC) change scenarios and analyzedthe results. The analysis showed that among all the LULC changes, agricultural technology that increasedcropland production had the greatest impact on SOC changes, followed by the tillage practices, changesin crop species, and the conversions of cropland to other land use. Information on management practiceinduced spatial variation in SOC can be useful for policy makers and farm managers to develop long-termmanagement strategies for increasing SOC sequestration in different areas

Triennial Report: 2012-2014

Triennial Report Purpose [Page] 3 Geographical Information Science Center of Excellence [Page] 5 SDSU Faculty [Page] 6 EROS Faculty [Page] 13 Research Professors [Page] 19 Postdoctoral Fellows [Page] 24 GSE Ph.D Program [Page] 36 Ph.D. Fellowships [Page] 37 Ph.D. Students [Page] 38 Recent Ph.D. Graduates [Page] 46 Masters Students [Page] 56 Previous Ph.D. Students [Page] 58 Center Scholars Program [Page] 59 Research Staff [Page] 60 Administrative and Information Technology Staff [Page] 62 Computer Resources [Page] 66 Research Funding [Page] 67 Glancing Back, Looking Forward [Page] 68 Appendix I Alumni Faculty and Staff Appendix II Cool Faculty Research and Locations Appendix III Non-Academic Fun Things To Do Appendix IV Publications 2012-2014 Appendix V Directory Appendix VI GIScCE Birthplace Map Appendix VII How To Get To The GIScC

Workshop on computer applications in water management: proceedings of the 1995 workshop

Compiled and edited by L. Ahuja, J. Leppert, K. Rojas, E. Seely.Also published as: Great Plains Agricultural Council publication, no. 154.Includes bibliographical references.Presented at the Workshop on computer applications in water management: proceedings of the 1995 workshop held on May 23-25, 1995 at Colorado State University in Fort Collins, Colorado

Assessing the Impacts of Land Use Change from Cotton (Gossypium hirsutum L.) to Cellulosic Bioenergy Crops on Watershed Hydrology and Water Quality in the Texas High Plains

The semi-arid Texas High Plains (THP) is one of the intensively managed agricultural regions in the United States (US) where cotton (Gossypium hirsutum L.) is a major crop. The THP region produces about a quarter of the US cotton. About 97% of the groundwater from the underlying Ogallala Aquifer is used for irrigating row crops including cotton in this semi-arid region. However, groundwater levels/quality in this region are experiencing a continuous decline/deterioration. This region also experiences recurring droughts and climate change studies predict warmer and drier summers in the future. These challenges may induce change in land use in the THP from high-water-demanding crops such as cotton to high water-and nitrogen-use-efficient cellulosic bioenergy crops such as perennial grasses and biomass sorghum [Sorghum bicolor (L.) Moench]. The region also holds enormous potential for the biofuel production according to the United States Department of Agriculture (USDA). The overall goal of this study is to assess the impacts of biofuel-induced land use change and climate change on hydrology, water quality and biomass production in the Double Mountain Fork Brazos watershed in the THP using the Soil and Water Assessment Tool (SWAT), Agricultural Policy/Environmental eXtender (APEX) and an integrated APEX-SWAT models. Switchgrass (Panicum virgatum L.) and Miscanthus × giganteus were found to be ideal bioenergy crops to replace cotton under the irrigated and dryland conditions, respectively. About 18 and 19 Mg ha^-1 yr^-1 of biomass could potentially be produced under the irrigated switchgrass and dryland Miscanthus scenarios. The land use change from cotton to perennial grasses decreased average annual (1994-2009) surface runoff, total nitrogen (TN) load through surface runoff and NO3-N leaching to groundwater by 88%, 86% and 100%, respectively and increased percolation by 28%. The climate change analysis indicated that the simulated annual irrigation water use and TN load under the future perennial grass land uses reduced by 60% and 30%, respectively, when compared to future cotton land use. However, under future climate scenarios, irrigated switchgrass yields were projected to reduce by 16-28% and dryland Miscanthus yields were simulated to increase by 32-38% when compared to the historic yields

Integrated Environmental Modelling Framework for Cumulative Effects Assessment

Global warming and population growth have resulted in an increase in the intensity of natural and anthropogenic stressors. Investigating the complex nature of environmental problems requires the integration of different environmental processes across major components of the environment, including water, climate, ecology, air, and land. Cumulative effects assessment (CEA) not only includes analyzing and modeling environmental changes, but also supports planning alternatives that promote environmental monitoring and management. Disjointed and narrowly focused environmental management approaches have proved dissatisfactory. The adoption of integrated modelling approaches has sparked interests in the development of frameworks which may be used to investigate the processes of individual environmental component and the ways they interact with each other. Integrated modelling systems and frameworks are often the only way to take into account the important environmental processes and interactions, relevant spatial and temporal scales, and feedback mechanisms of complex systems for CEA. This book examines the ways in which interactions and relationships between environmental components are understood, paying special attention to climate, land, water quantity and quality, and both anthropogenic and natural stressors. It reviews modelling approaches for each component and reviews existing integrated modelling systems for CEA. Finally, it proposes an integrated modelling framework and provides perspectives on future research avenues for cumulative effects assessment