Evapotranspiration Mapping for Forest Management in California's Sierra Nevada

We assessed the response of densely forested watersheds with little apparent annual water limitation to forest disturbance and climate variability, by studying how past wildfires changed forest evapotranspiration, and what past evapotranspiration patterns imply for the availability of subsurface water storage for drought resistance. We determined annual spatial patterns of evapotranspiration using a top-down statistical model, correlating measured annual evapotranspiration from eddycovariance towers across California with NDVI (Normalized Difference Vegetation Index) measured by satellite, and with annual precipitation. The study area was the Yuba and American River watersheds, two densely forested watersheds in the northern Sierra Nevada. Wildfires in the 1985-2015 period resulted in significant post-fire reductions in evapotranspiration for at least 5 years, and in some cases for more than 20 years. The levels of biomass removed in medium-intensity fires (25- 75% basal area loss), similar to magnitudes expected from forest treatments for fuels reduction and forest health, reduced evapotranspiration by as much 150-200 mm yr-1 for the first 5 years. Rates of recovery in post-wildfire evapotranspiration confirm the need for follow-up forest treatments at intervals of 5-20 years to sustain lower evapotranspiration, depending on local landscape attributes and interannual climate. Using the metric of cumulative precipitation minus evapotranspiration (P-ET) during multi-year dry periods, we found that forests in the study area showed little evidence of moisture stress during the 1985-2018 period of our analysis, owing to relatively small reliance on interannual subsurface water storage to meet dry-year evapotranspiration needs of vegetation. However, more-severe or sustained drought periods will push some lower-elevation forests in the area studied toward the cumulative P-ET thresholds previously associated with widespread forest mortality in the southern Sierra Nevada

Long-Term Assessment of Climate Change Impacts on Tennessee Valley Authority Reservoir Operations: Norris Dam

Norris Reservoir is the oldest and largest reservoir maintained and operated by the Tennessee Valley Authority (TVA). Norris Dam received a new operating guide in 2004; however, this new guide did not consider projected climate change. In an aging infrastructure, the necessity to assess the potential impacts of climate change on water resources planning and management is increasing. This study used a combined monthly hydrologic model and a general circulation model’s (GCM) outcome to project inflows for three future time spans: 2030s, 2050s, and 2070s. The current operating guide was then assessed and optimized using penalty-function-driven genetic algorithms to gain insight for how the current guide will respond to climate change, and if it can be further optimized. The results showed that the current operating guide could sufficiently handle the increased projected runoff without major risk of dam failure or inundation, but the optimized operating guides decreased operational penalties ranging from 22 to 37 percent. These findings show that the framework used here provides water resources planning and management a methodology for assessing and optimizing current systems, and emphasizes the need to consider projected climate change as an assessment tool for reservoir operations

Long-Term Evaluation of Norris Reservoir Operation Under Climate Change

This study aimed to address the potential long-term effects of future climate change on the Tennessee Valley Authority’s (TVA’s) operation policy for Norris Reservoir. The Community Earth System Model 1.0 (CESM1.0), a general circulation model (GCM) accessible through the Intergovernmental Panel on Climate Change’s (IPCC’s) Coupled Model Intercomparison Project Phase 5 (CMIP5), with the Representative Concentration Pathway 4.5 (RCP4.5) was used to obtain projected precipitation and temperature data for three future climate scenarios, 2030’s, 2050’s, and 2070’s. Three hydrologic models were individually calibrated on 30 years of observed runoff data and combined utilizing linear programming to consider the strengths of each model. Inflow hydrographs were simulated for the future time spans using projected precipitation and temperature. Reservoir routing was then simulated using the inflow hydrographs via mass balance and the current operation policy to determine the storage elevation of the reservoir. Next, the routing simulations were utilized as input for a genetic algorithm forced optimization model, to minimize an elevation-based penalty value, optimizing Norris Reservoir’s operation policy. Finally, the operation performance of Norris Reservoir’s current operation policy versus the policies generated by the developed optimization model for each projected scenario were evaluated. The results suggested a 20.7, 23.8, and 24.3 percent increase in runoff for the 2030’s, 2050’s, and 2070’s, respectively. Although the current policy was able to support this increase in runoff, the optimization model decreased operation penalties by 23.3, 22.2, and 24.4 percent for the 2030’s, 2050’s and 2070’s, respectively. These results can provide substantial insight to TVA hydrologists and decision makers that their current policy may require re-evaluation, considering the potential impacts of climate change

Long-Term Assessment of Climate Change Impacts on Tennessee Valley Authority Reservoir Operations: Norris Dam

Norris Reservoir is the oldest and largest reservoir maintained and operated by the Tennessee Valley Authority (TVA). Norris Dam received a new operating guide in 2004; however, this new guide did not consider projected climate change. In an aging infrastructure, the necessity to assess the potential impacts of climate change on water resources planning and management is increasing. This study used a combined monthly hydrologic model and a general circulation model’s (GCM) outcome to project inflows for three future time spans: 2030s, 2050s, and 2070s. The current operating guide was then assessed and optimized using penalty-function-driven genetic algorithms to gain insight for how the current guide will respond to climate change, and if it can be further optimized. The results showed that the current operating guide could sufficiently handle the increased projected runoff without major risk of dam failure or inundation, but the optimized operating guides decreased operational penalties ranging from 22 to 37 percent. These findings show that the framework used here provides water resources planning and management a methodology for assessing and optimizing current systems, and emphasizes the need to consider projected climate change as an assessment tool for reservoir operations

Internet of Things for Water Sustainability

The water is a finite resource. The issue of sustainable withdrawal of freshwater is a vital concern being faced by the community. There is a strong connection between the energy, food, and water which is referred to as water-food-energy nexus. The agriculture industry and municipalities are struggling to meet the demand of water supply. This situation is particularly exacerbated in the developing countries. The projected increase in world population requires more fresh water resources. New technologies are being developed to reduce water usage in the field of agriculture (e.g., sensor guided autonomous irrigation management systems). Agricultural water withdrawal is also impacting ground and surface water resources. Although the importance of reduction in water usage cannot be overemphasized, major efforts for sustainable water are directed towards the novel technology development for cleaning and recycling. Moreover, currently, energy technologies require abundant water for energy production. Therefore, energy sustainability is inextricably linked to water sustainability. The water sustainability IoT has a strong potential to solve many challenges in water-food-energy nexus. In this chapter, the architecture of IoT for water sustainability is presented. An in-depth coverage of sensing and communication technologies and water systems is also provided

Long-Term Assessment of Climate Change Impacts on Tennessee Valley Authority Reservoir Operations: Norris Dam

Norris Reservoir is the oldest and largest reservoir maintained and operated by the Tennessee Valley Authority (TVA). Norris Dam received a new operating guide in 2004; however, this new guide did not consider projected climate change. In an aging infrastructure, the necessity to assess the potential impacts of climate change on water resources planning and management is increasing. This study used a combined monthly hydrologic model and a general circulation model’s (GCM) outcome to project inflows for three future time spans: 2030s, 2050s, and 2070s. The current operating guide was then assessed and optimized using penalty-function-driven genetic algorithms to gain insight for how the current guide will respond to climate change, and if it can be further optimized. The results showed that the current operating guide could sufficiently handle the increased projected runoff without major risk of dam failure or inundation, but the optimized operating guides decreased operational penalties ranging from 22 to 37 percent. These findings show that the framework used here provides water resources planning and management a methodology for assessing and optimizing current systems, and emphasizes the need to consider projected climate change as an assessment tool for reservoir operations

Estimating plant-accessible water storage through evaluating evapotranspiration in the semi-arid western United States using eddy-covariance, remote sensing, and spatially distributed data

The studies within this dissertation use a suite of long-term flux-tower, remotely sensed, and spatially distributed data to more accurately assess the withdrawal of subsurface plant-accessible water storage during multi-year dry periods, more accurately represent measurements of evapotranspiration across the landscape, and examine how vegetation use of plant-accessible water storage varies along latitudinal and elevation gradients, and with time. First, a suite of flux towers from across the arid and semi-arid western United States were used to assess the response of evapotranspiration under varying climates and vegetation types to drought. Here we found that regions experiencing a Mediterranean climate are substantially more dependent on subsurface storage than those receiving a summer monsoon, but available plant-accessible subsurface water storage in the Mediterranean climates can support evapotranspiration for the entirety of a multi-year dry period at some locations. It was also discovered that a transition from snow to rain could increase dependency vegetation on plant-accessible subsurface water storage by as much as 20\% at energy-limited, snow-dominated sites. Next, measurements of evapotranspiration were distributed across the 14 river basins draining into California$'$s Central Valley. This was performed by expanding on current remotely sensed-based methods to include climatic data and consider vegetation type. This novel approach decreased the root-mean-square error by 31-50\% when compared to methods only using NDVI and was insensitive to the spatial resolution of data used. This product showed that evapotranspiration was greatest in the northern basins, peaking at lower elevations, and decreased in magnitude while peaking at higher elevations as latitude decreased. It was also revealed that runoff was derived in primarily one of two ways in this region, the rain-dominated north where annual rainfall grossly exceeds annual evapotranspiration; and the snowmelt-driven south where most precipitation contributes to high-elevation snowpack in energy-limited areas. Finally, the 14 basins draining into California$'$s Central Valley could be binned into four groups based upon what water-balance components and climatic variables were most highly correlated with changes in subsurface water storage, the northernmost, northern, mid-range and southern basins. The results showed that the southern basins may have already reached a critical threshold in storage drawdown, explaining why tree mortality is so widespread in the region, and that the northern and northernmost basins will likely follow a similar path if measures are not taken to reduce evapotranspiration. The studies in this dissertation provided comprehensive analyses of how evapotranspiration spatially varies and how its response to climate extremes alters the hydrologic cycle. Spatial products are in high demand for water resources and forest management applications, and although quantifying uncertainties remain a challenge, these products provide substantial value to improving our understanding of the water cycle

Evapotranspiration and Runoff Patterns Across California's Sierra Nevada

Spatially resolved annual evapotranspiration was calculated across the 14 main river basins draining into California's Central Valley, USA, using a statistical model that combined satellite greenness, gridded precipitation, and flux-tower measurements. Annual evapotranspiration across the study area averaged 529 mm. Average basin-scale annual precipitation minus evapotranspiration was in good agreement with annual runoff, with deviations in wet and dry years suggesting withdrawal or recharge of subsurface water storage. Evapotranspiration peaked at lower elevations in the colder, northern basins, and at higher elevations in the southern high-Sierra basins, closely tracking the 12.3°C mean temperature isocline. Precipitation and evapotranspiration are closely balanced across much of the study region, and small shifts in either will cause disproportionate changes in water storage and runoff. The majority of runoff was generated below the rain-snow transition in northern basins, and originated in snow-dominated elevations in the southern basins. Climate warming that increases growing season length will increase evapotranspiration and reduce runoff across all elevations in the north, but only at higher elevations in the south. Feedback mechanisms in these steep mountain basins, plus over-year subsurface storage, with their steep precipitation and temperature gradients, provide important buffering of the water balance to change. Leave-one-out cross validation revealed that the statistical model for annual evapotranspiration is sensitive to the number and distribution of measurement sites, implying that additional strategically located flux towers would improve evapotranspiration predictions. Leave-one-out with individual years was less sensitive, implying that longer records are less important. This statistical top-down modeling of evapotranspiration provides an important complement to constraining water-balance measurements with gridded precipitation and unimpaired runoff, with applications such as quantifying water balance following forest die-off, management or wildfire