Progress report for GNC21-331
Project Information
Groundwater irrigation has been regarded as critical to the sustenance of agricultural production in the U.S. Midwest. Due to continuous extraction, many agricultural regions with heavy reliance on groundwater irrigation have witnessed substantial drawdown or depletion of groundwater reservoirs. To develop effective coping strategies, it is critical to have a thorough understanding of the groundwater system and its interaction with groundwater users and future challenges such as climate variability and change. Thus, this project aims to develop a socio-hydrological modeling framework for examining the sustainability of aquifers in irrigation agricultural landscapes and evaluating potential solutions to improve resilience in a changing climate.
This project will develop a transferrable modeling framework that can: (1) characterize both hydrologic dynamics and producers’ irrigation behaviors, (2) integrate hydrologic and social-behavioral models to represent the integrated system dynamics, and (3) evaluate groundwater sustainability under future climate scenarios. The modeling framework will couple (a) an agent-based model (ABM) for simulating irrigation behaviors in response to physical constraints and hydrological models for characterizing surface processes and groundwater dynamics. Such a framework can be used to examine the interactions between human and water systems with incomplete or ambiguous information on irrigation decision making. The ABM allows the representation of complex decision-making processes by defining collective actions using predefined behavioral rules. Using a Central Platte River basin as the testbed, the Cooperative Hydrology Study (COHYST) groundwater model and a Soil & Water Assessment Tool (SWAT) model developed by the applicant will be utilized to simulate groundwater storage dynamics and to model groundwater recharge rate at different spatial and temporal scales. The ABM shall then be coupled with the hydrologic models to represent the integrated system dynamics. The project is expected to produce outcomes that will be critical to sustainable agriculture in the North Central Region. The expected outcomes encompass tools and information that will help increase awareness, change attitudes, and inform decisions and policies in groundwater management and sustainability. It will improve the understanding of the effects of potential agricultural and water management options on groundwater storage, and allow a better design of intervention strategies to mitigate foreseeable climate impacts on groundwater depletion.
The project outcomes include (1) the critical information that links producers’ irrigation behaviors to the prospect of groundwater sustainability, and (2) a new decision-making tool that allows natural resources agencies to evaluate the impact of future climate and the effectiveness of groundwater management options. First, we expect the producers to increase their awareness of risks to groundwater sustainability imposed by unrestrictive pumping activities and future climate change. Using a range of project dissemination avenues (e.g., local board meetings, flyers, farming group emails, and social media), we expect to change the perception and attitudes of producers towards groundwater resources: from an unlimited reservoir to a limited and vulnerable resource that requires proactive protection. Second, we expect the state and regional natural resources agencies to use the modeling framework as a tool to inform water management options and intervention strategies to mitigate groundwater depletion. Our project findings are expected to facilitate more effective science-based policies to maximize the crop production benefits while allow sustainable water use over short and long terms. This will result in shared groundwater sustainability goals of different conservation programs and policies being put in place for the North Central region.
Research
In my research, I use a socio-hydrological framework to examine groundwater and how people interact with it and make decisions related to it. In theory, socio-hydrological modeling frameworks should assess how humans and groundwater co-evolve, interact, and respond under different circumstances and challenges. In practice, however, most modeling frameworks fail to adequately represent the intertwined groundwater and human systems, especially human behavior due to the use of over-simplified models.
To address this gap, my research combines both natural science and social science methods. I do this by integrating hydrologic models with an agent-based model. As shown in the figure below, it features a social system model (Agent-based Model) for characterizing behaviors of groundwater irrigation and coupled watershed-aquifer models (Soil and Water Assessment Tool (SWAT) and MODFLOW) for modeling surface water and groundwater interactions. The construction of the ABM shall be informed by interviews and surveys to adequately capture and represent human decision-making.
This framework accounts for the feedback and dynamics within and between the human and the water systems. It also makes it possible to make projections and reconstructions to test different ‘what if’ scenarios. One section of this framework was utilized to study the impacts of cover crops and climate change on water dynamics in our study area. The objective of the study was to improve the understanding of the long-term impacts of cover crops in combination with climate change on agricultural water management in an agricultural system following a hydrological modeling framework. To achieve this objective, the Soil and Water Assessment Tool (SWAT) modeling and water footprint analyses were conducted.
The SWAT model was developed for the Central Platte River Basin for the purposes of simulating and evaluating the hydrological system in terms of both water quantity and quality. The Soil and Water Assessment Tool (SWAT) model (Version 2012) was used to cover the 27-year period from 1989 to 2015. Key inputs to the SWAT model included weather (i.e., precipitation, solar radiation, temperature, relative humidity, and wind speed) data, topography, soils data, and land cover (Table 1), as well as typical land management practices in the region. All the inputs were downloaded from either state, national or academic agencies. The coordinate system for all the input data was set to North American Datum 1983 (NAD83) Universal Transverse Mercator Zone 14 N.
Table 1: Data and sources
|
Data Type |
Resolution |
Source |
Variable |
|
Climate |
Daily |
HPRCC AWDN PRISM https://gdo-dcp.ucllnl.org/downscaled_cmip_projections |
Precipitation(mm/d), maximum and minimum temperature (0C), solar radiation (MJ/m2), relative humidity (fractional), and wind speed (m/s) Future climate projections (Precipitation(mm/d), maximum and minimum temperature (0C)) |
|
Topography |
30 m |
USDA-NRCS National Elevation Data 30 meter |
30-meter Digital Elevation Model (DEM) |
|
Land use |
30 m |
Cropland Data Layer & UNL CALMIT data (1982) |
Crop types |
|
Soil |
10 m |
USDA/NRCS Geospatial Data Gateway |
SWAT US SSURGO soils Database; gSSURGO spatial and tabular data
|
|
Streamflow |
Daily |
Gages from U.S Geological Survey, NeDNR, and the COHYST project |
Flow (m3/s) |
The SWAT model requires a wide range of inputs including spatial data and weather data. Table 1 shows the provided data and respective sources for the case study. It includes climate, agriculture management, as well as remotely sensed spatial (e.g. DEM, soil and land use) information.
In this study, the management practices selected to represent the agricultural conditions were fertilizer application, irrigation, planting operation, harvest and kill operations as well as the incorporation of rye after cash crop (corn and soybean) harvest. Planting and harvesting dates were obtained from literature and communication with local experts. Irrigation and fertilizer application were set up using the automatic option. Therefore, irrigation events were triggered by water stress threshold (soil moisture deficit) and fertilizer was applied based on nutrients stress factor. Auto fertilizer and auto irrigation options of the SWAT model were used based on the assumption that farmers were using good management practices.
Table 2: SWAT model cover crop scenarios
|
SWAT model scenario |
Year |
Operation |
Crop |
Date |
|
|
Month |
Day |
||||
|
Baseline (NWCC) |
1 |
Plant begin |
Corn |
May |
15 |
|
|
1 |
Harvest and kill |
Corn |
October |
10 |
|
|
1 |
Plant begin |
Soybean |
May |
15 |
|
|
|
Harvest and kill |
Soybean |
October |
15 |
|
Winter cover crop (WCC) |
1 |
Plant begin |
Corn |
May |
15 |
|
|
1 |
Harvest and kill |
Corn |
October |
10 |
|
|
1 |
Plant begin |
Cereal rye |
October |
15 |
|
|
1 |
Harvest and kill |
Cereal rye |
May |
10 |
|
|
1 |
Plant begin |
Soybean |
May |
15 |
|
|
1 |
Harvest and kill |
Soybean |
October |
15 |
|
|
1 |
Plant begin |
Cereal rye |
October |
15 |
|
|
1 |
Harvest and kill |
Cereal rye |
May |
10 |
This study assessed 38 General Circulation Models (GCMs) from the Fifth Coupled Model Intercomparison Project (CMIP5; Taylor et al. 2012). This represented the set of GCMs that were available, contained daily data from 1950 to 2100, and included historical and future outputs for both the moderate and high representative concentration pathways (RCP4.5 and RCP8.5, respectively; Moss et al. 2010; Knutti 2014). GCM projections of temperature change were calculated as absolute differences (future - current) while projections of future precipitation are calculated as relative changes of the current period (future/current * 100%). The annual precipitation and temperature changes were calculated for the period between 2030−2050, referenced to 1950−1980.
Table 3: Selected representative GCMs
|
Classification |
Climate Model |
RCP |
Precipitation |
Temperature |
|
Hot & Wet |
canesm2.1. |
4.5 |
38% |
2.2 |
|
8.5 |
41% |
1.3 |
||
|
Cool & Dry |
inmcm4.1. |
4.5 |
30% |
1.9 |
|
8.5 |
14% |
2.1 |
||
|
Hot & Dry |
ipsl-cm5a-mr.1. |
4.5 |
28% |
2.3 |
|
8.5 |
8% |
3 |
||
|
Central Tendency |
mpi-esm-mr.1. |
4.5 |
34% |
2 |
|
8.5 |
32% |
2.5 |
||
|
Cool & Wet |
mri-cgcm3.1. |
4.5 |
30% |
0.4 |
|
8.5 |
33% |
0.7 |
The SWAT modeling framework is shown below:
The SWAT model outputs were utilized to assess the impacts of cover crops and climate change on water dynamics. The figure below illustrates the components used in our analysis:
The development of the social system model is still underway. To develop the ABM that represents local irrigation decision-making, we propose to design and conduct interviews and mail surveys following a Theory of Planned Behavior (TPB) framework. TPB, developed by Ajzen (1991) poses that the intention to perform is dependent upon three constructs: attitude, subjective norms, and perceived behavioral control. The theory’s concise and efficient structure makes it ideal for analyzing decision-making behaviors from information collected from the study area through interactions with stakeholders via interviews and surveys.
A sample of the research subjects was approached for interviews during the development of the survey instrument. Based on their insights, the survey was revised and updated in preparation for the first round of mailing. We expect to use the data and relevant literature (e.g., irrigation pumping records, published survey results) to refine behavioral rules of irrigators and the causal relations that lead to irrigation decisions, which will ultimately be used to inform the design of ABM.
The ABM will then be coupled with hydrological models (Cooperative Hydrology Study (COHYST) groundwater model and SWAT model) to address the interaction between irrigation decision-making processes and hydrological processes. To couple both COHYST model and SWAT model, we will adopt an existing SWAT-MODFLOW integration tool (Wei, et al., 2018). In the integrated framework, the hypotheses about irrigation behavioral rules and/or decision-making mechanisms and the scenarios of management practices (e.g., irrigation quota and groundwater banking) and climate scenarios (e.g., drier climate) can be examined quantitatively.
The blue water consumed in the CPNRD basin under the winter cover crop (WCC) scenario were generally low in midstream sub-basins with higher values occurring in the upstream and downstream subbasins. On the other hand, green water flow (ET) was higher in the midstream as well as at the subbasins downstream. The blue water flows in the CPNRD basin were generally reduced in the downstream sub-basins under the WCC scenarios. In the WCC scenario, the blue water flow downstream was lower. The likely contributing factors are precipitation and land cover type. In downstream sub-basins, precipitation is generally high following the west-east precipitation gradient. These results in relatively large amounts of runoff and blue water flows which are lower under WCC than no winter cover crop (NWCC). In upstream sub-basins, precipitation is lower thus runoff is small and hence blue water flows are lower.
In the study, the temporal changes of selected hydrological components under WCC scenario: Evapotranspiration (ET), Surface runoff (SURQ_GENmm), and Groundwater recharge (GW_RCHG) obtained from the well-calibrated SWAT model was also examined at annual and monthly time scales. These components were analyzed to assess the impact of the winter cover crop installation. For the baseline (1994-2014), ET increased in the winter cover crop growing season (October to April) compared to the scenario without the cover crop. This concurs with several studies that report increases in ET with the addition of a crop in the fields which would otherwise be bare. The simulation results indicate that rye cover crops reduced annual surface runoff and recharge to the aquifer by 48% and 53% respectively, while increasing annual evapotranspiration (ET) by 25 %.
Figure 1: Inter-annual
Figure 2: Intra-annual
The impact of a winter cover crop installation was next assessed under the selected climate scenarios i.e., hot and wet, hot and cool, cool and wet, cool and dry, and central tendency (RCP 4.5 and 8.5). ET generally showed increases in all the scenarios ranging between 4% to 8% . The results also indicated that surface runoff, and groundwater recharge would decrease in the future for all climate scenarios. The reduction in surface runoff ranged between 29% to 46% with accompanying reductions in recharge ranging between 20% to 30%. The reductions in surface runoff may be attributed to increased infiltration of precipitation and utilization of soil moisture content by the cover crops. The increase in ET with the cover crop installation shown in this study concurs with several studies (Qi et al., 2011; Nielsen et al., 2015; Basche et al., 2016). The same applies to the reduction in runoff with accompanying reductions in recharge. In their analysis of the impact of land use and land cover changes on groundwater recharge and surface runoff, Owuor et al., (2016) reported several experimental studies with similar findings.
The spatial distribution of the changes in selected water balance components was mapped out to determine the hotspots. There was a significant reduction of runoff under the various climate scenarios after the installation of a winter cover crop. The spatial patterns of runoff reduction showed the highest changes in the subbasins located in the central parts of the basin for most of the climate scenarios. Particular attention was focused on the wet scenarios and subbasins that are situated closer to the river due to higher risk of erosion associated with higher precipitation.
The changes in groundwater recharge generally followed a similar trend (see figure below) with most scenarios showing the highest reductions occurring in the central parts of the basin.
We are still working on the survey and agent-based model which will be integrated with the hydrologic models.
Educational & Outreach Activities
Participation Summary:
In December 2021, I gave a virtual presentation at the American Geophysical Union (AGU) Fall Meeting sharing the preliminary findings from my research. I developed and calibrated a Soil and Water Assessment Tool (SWAT) hydrological model to help improve the understanding of the long-term impacts of cover crops in combination with climate change on the agricultural water management in agricultural systems. A combination of cover crop practices and climate change scenarios was examined using a SWAT-based water footprint assessment. I mainly shared the preliminary results that showed the impact of installing cover crops on soil-water dynamics and evapotranspiration in a semiarid agricultural region in Central Nebraska.
In April 2022, I was invited to the Southern Illinois University Sustainability Celebration to speak about my research. I was able to talk to students and faculty about the importance of groundwater, the challenges facing groundwater sustainability, and the importance of tackling these challenges now. I also talked about the methods that I am using for my research, the expected results, and their importance in addressing the challenges facing groundwater.
In October 2022, I presented additional results of my study on the impact of installing cover crops on soil-water dynamics and evapotranspiration at the Association of American Geographers (AAG) West Lakes Division Annual Meeting. The presentation garnered a lot of interest due to the reported impacts of the cover crop not only on soil water dynamics and evapotranspiration but also their impacts on climate change impact mitigation.
Currently, we are in the process of finalizing an educational pamphlet on groundwater sustainability to be disseminated to producers via a collaboration with the CPNRD. We are also finalizing an article reporting the results from the study of cover crop impacts yielded from the SWAT model to be submitted to a journal for publication.
Project Outcomes
This project aims to increase awareness of risks to groundwater sustainability imposed by unrestrictive pumping activities and future climate change. Using a range of project dissemination avenues (e.g., presentations, flyers, farming group emails, and social media), we expect to change the perception and attitudes of producers towards groundwater resources: from an unlimited reservoir to a limited and vulnerable resource that requires proactive protection. Second, we expect the state and regional natural resources agencies to use the modeling framework as a tool to inform water management options and intervention strategies to mitigate groundwater depletion.
One specific example is our current study under preparation for publication which examines one option to support sustainable agriculture. Sustainable cropping practices have emerged as a beneficial alternative to conventional cropping measures with growing popularity among farmers, researchers, and government agencies (Islam et al., 2006). Focus has been placed on those climate-resilience practices that mitigate the risks from excess rainfall and drought events (Stewart and Peterson, 2015). Cover crops have been recommended to help mitigate climate change impacts due to their ability to increase water infiltration while reducing runoff and soil evaporation. (Unger and Vigil, 1998; Qi et al. 2011a; Nielsen et al. 2015; Eshel et al. 2015; Yu et al. 2016). Additionally, cover crops have been found to positively impact physical and chemical soil properties, thus improving soil productivity and soil water storage capacity (Kay, 1998; Basche et al., 2016a). They also have numerous positive environmental impacts such as weed suppression and the sequestration of nutrients (Unger and Vigil, 1998; Bergtold et al., 2012; Kladivko et al., 2014). As a result, cover crops have increasingly been recommended in annual cropping systems (e.g., maize and soybeans) (Basche et al., 2016a; Kaspar and Singer, 2011). However, despite many studies agreeing on the effects of cover crops on the water balance components, there is still a lack of consensus on the magnitude of these effects. Additionally, it is still unclear whether a regional installation of cover crops is a viable option to counteract the negative impacts of climate change on agricultural water availability. My study seeks to address these and other gaps in knowledge for farmers as well as policymakers. Our project findings are expected to facilitate more effective science-based policies to maximize the crop production benefits while allowing sustainable water use over short and long terms. This will result in shared groundwater sustainability goals of different conservation programs and policies being put in place for the North Central region.