Browsing by Subject "Rainfall"

Now showing 1 - 5 of 5
  • Thumbnail Image
    Item
    Determination of Effective Impervious Area in Urban Watersheds
    (2015-08) Ebrahimian, Ali
    Impervious surfaces have been identified as an indicator of the impacts of urbanization on water resources. The design of stormwater control measures is often performed using the total impervious area (TIA) in a watershed. Recent studies have shown that a better parameter for these designs is the " effective"� impervious area (EIA), or the portion of total impervious area that is hydraulically connected to the storm sewer system. Methods to improve estimates of EIA are not highly researched, and need further investigation. The overall goal of this project is to develop a method to estimate EIA in urban watersheds with data that is readily available. First, the existing rainfall-runoff method was improved by reducing the uncertainty associated with EIA estimates and applying it to 40 gauged urban watersheds with different sizes and hydrologic conditions, mostly in the Twin Cities metro area of MN and Austin, TX. The results are then utilized to develop a new method based on the integration of GIS and Curve Number (CN). The GIS-CN method is applicable to ungauged watersheds and is able to estimate EIA fraction based on TIA and hydrologic soil group (HSG). The results are used to evaluate the potential and the limitations of the GIS-CN method. The outcome and applications of this study improves the rainfall-runoff modelling in urban watersheds and will eventually lead to the design of a more sustainable urban stormwater infrastructure.
  • Thumbnail Image
    Item
    Determination of Effective Impervious Area in Urban Watersheds
    (Center for Transportation Studies, University of Minnesota, 2015-07) Ebrahimian, Ali; Gulliver, John S.; Wilson, Bruce N.
    Impervious surfaces have been identified as an indicator of the impacts of urbanization on water resources. The design of stormwater control measures is often performed using the total impervious area (TIA) in a watershed. Recent studies have shown that a better parameter for these designs is the “effective” impervious area (EIA), or the portion of total impervious area that is hydraulically connected to the storm sewer system. Methods to improve estimates of EIA are not highly researched, and need further investigation. The overall goal of this project is to develop a method to estimate EIA in urban watersheds with data that is readily available. First, the existing rainfall-runoff method was improved by reducing the uncertainty associated with EIA estimates and applying it to 40 gauged urban watersheds with different sizes and hydrologic conditions, mostly in the Twin Cities metro area of MN and Austin, TX. The results are then utilized to develop a new method based on the integration of GIS and Curve Number (CN). The GIS-CN method is applicable to un-gauged watersheds and is able to estimate EIA fraction based on TIA and hydrologic soil group (HSG). The results are used to evaluate the potential and the limitations of the GIS-CN method. The outcome and applications of this study improves the rainfall-runoff modelling in urban watersheds and will eventually lead to the design of a more sustainable urban stormwater infrastructure.
  • Thumbnail Image
    Item
    Modeling the impact of iIrrigation on precipitation over the Great Plains.
    (2011-08) Harding, Keith John Iliff
    Since World War II, the rapid expansion of irrigation throughout the Great Plains has threatened the sustainability of the Ogallala Aquifer. Irrigation has been shown to modify the surface energy and water budgets over the Great Plains by altering the partitioning of latent and sensible heating. An increase in latent heating from irrigation contributes to a cooler and more humid surface, which has competing impacts on convection. In this study, the Weather Research and Forecasting model was modified to simulate the effects of irrigation at sub-grid scales. Nine April-October simulations were completed for different hydrologic conditions over the Great Plains. Data from these simulations was assimilated into a back-trajectory analysis to identify where evapotranspired moisture from irrigated fields predominantly falls out as precipitation. May through September precipitation increased on average over the Great Plains by 4.97 mm (0.91%), with the largest increases during wet years (6.14 mm; 0.98%) and the smallest increases during drought years (2.85 mm; 0.63%). Large precipitation increases occurred over irrigated areas during normal and wet years, with decreases during drought years. On average, only 15.8% of evapotranspired moisture from irrigated fields fell out as precipitation over the Great Plains, resulting in 5.11 mm of May-September irrigation-induced precipitation. The heaviest irrigation-induced precipitation occurred over north-central Nebraska, coincident with simulated and observed precipitation increases. While irrigation resulted in localized and region-wide increases in precipitation, large evapotranspiration increases suggest that irrigation contributes to a net loss of water in the Great Plains.
  • Thumbnail Image
    Item
    Soil health system impacts on soil hydraulic functions in southern Minnesota
    (2023-12) Tangen, Bailey
    Soil health management systems use agricultural practices incorporating living roots, persistent surface cover, diverse crop rotations, and minimal soil disturbance. These systems are widely believed to improve soil hydraulic functions. However, intense rainfall can cause physical slaking of aggregates, loss of surface pores, and reduced hydraulic functions. Soil health management systems correlate with stable aggregates and large soil pores, but it is not clear how these properties change with rainfall in fine-textured soil profiles in southern Minnesota, United States. Therefore, quantifying the hydraulic function of these systems is important as climate change intensifies growing season rainfall. Here, we investigated soil health system’s volumetric soil water content and aggregates’ response to rainfall. During 2021 and 2022, we collected data from five tillage and cover crop treatments in replicated plots at the Southern Research and Outreach Center in Waseca, MN, and paired conventional and soil health systems at three long-term on-farm sites (≥5 years, clay loam and silt loam soils). We monitored volumetric soil water content and soil aggregates within 24 hours before and 24 and 72 hours after select rainfall events. Across all locations, drier conditions led to greater rainfall capture. Differences in response to rain were found between the paired farm treatments. Generally, conventional sites had 5-20% more small aggregates following rain than soil health sites, but this effect was inconsistent across all locations. Soil health systems generally retained 10-30% more large water-stable aggregates than conventional systems in response to rain. Based on soil water retention curves, soil health treatments trended 2.5-12.5% more macroporosity than conventional systems, likely contributing to the water capture. At the farms, greater microporosity and connectivity led to 0.25-2 cm/hr greater unsaturated hydraulic conductivity relative to soil health sites, validating the greater macroporosity results we found in the soil health sites. Despite long-term treatment history at SROC, there was no unsaturated hydraulic conductivity difference, though trends showed a positive relationship with increased disturbance, like rip/chisel. Soil health indicators were higher for the soil health system of one on-farm site, where soil health practices included 30 years of long-term no-till and cover crops compared to moldboard plowing. This research indicates the importance of holistically incorporating soil health practices into field systems for achieving soil functions.
  • Thumbnail Image
    Item
    Three Essays in Agricultural Economics
    (2022-07) Boyd Leon, Chris
    The three essays that compose this dissertation are on the topic of risk in agriculture in developing countries, where farmers are completely exposed to these risks. The first two chapters focus on price risk and the third focuses on the risk derived from atypical rainfall levels. In the first essay, I address the impacts of a temporary price support policy (a policy that stabilizes and increases prices), in Peru, on the welfare of farmers it aimed to benefit. I exploit the geographical discontinuity of the policy to casually estimate its impacts using differences-in-differences. I find that although the average potato farmer did not significantly change their total consumption due to the policy, the groups of net consumers, farmers with larger shares of potato on total farm sales, and larger farmers increase their consumption due to the price support. Moreover, I find these positive impacts vanish or become negative one year after the policy implementation, suggesting that price support policies are only effective in the short run and for farmers with certain characteristics. In the second essay, I study the production behavior of farmers when introducing a price insurance, i.e., an insurance that stabilizes prices and increases low prices. To assess the causal and pure impact of price risk and price insurance on production behavior, I run an artefactual lab-in-the-field experiment with farmers in Peru. In the experiment, farmers played three games in random order: a baseline game where only price risk exists and it is introduced randomly; a second game where both price risk and an actuarially fair mandatory price insurance exist; and a third game where price risk and the price insurance exist, but the insurance is voluntary and random discounts (of 0%, 50%, or 100%) on the premium are offered. My results suggest that, on average, (i) price risk does not significantly change production relative to price certainty and (ii) neither does the provision of compulsory insurance against price risk, but (iii) the introduction of voluntary insurance causes the average producer on the market to produce more in situations of price risk than in situations of price certainty. Additionally, I find that even in the absence of premium discounts, the insurance against price risk would have a large (i.e., 70-percent) take-up rate. In the third essay, I study how rainfall shocks (i.e., rainfall deviations from the mean) affect rural labor and child health, and I assess the role of mothers’ time use on child nutrition, among rural families in Uganda. My results show that less rainfall in the last month decreases mothers’ timeshare in housework, increases her share in other household-related activities (e.g., fetching water), and does not change her timeshare at the household farm. Less rainfall in the last month also decreases child nutrition. Nonetheless, using mediation analysis, I find that none of the mother’s time-use variables appears to be a mediating factor between rainfall variability and child nutrition. These results suggest that mothers adjust their time-use due to rainfall variability with the objective of preserving their children’s nutrition levels.