Integrating Water, Flood, and Stormwater Management Infrastructures with Enhanced Observations and Forecasting

A Climate Context for Water Management: Risk Management and Extremes in Arid Southwest

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Abstract:

Managing climate risks involves understanding issues ranging from perceptions of risk and human behavior to the underlying climate science and how to handle uncertainties associated with climate projections. Changes in the hydrologic cycle are the main way that people across the globe are experiencing climate change, ranging from drought, to extreme precipitation, to sea level rise and increased intensity of tropical storms. Extreme events are the "wake-up call" for climate change, and they are becoming increasingly expensive both in economic terms and in the context of natural ecosystems. Being better prepared for them requires considering the likely increase in low probability-high consequence events. Although it is contrary to the training of most water managers, considering the "tails" of the distribution of events is important (floods, droughts, fires, tropical storms, atmospheric rivers, etc.). This is best done through scenario planning — considering a range of different futures from both a climate and a socio-economic perspective, and by considering the implications for all aspects of water management, including strategic planning, business practices, infrastructure, etc. This presentation will include some approaches used and outputs from the Colorado River Conversations Project at the University of Arizona. This Walton-funded project is helping to expose a number of issues associated with cascading risks from climate impacts and the possible intersection of climate impacts with other events related to governance, the economy, etc.

Use of Green Infrastructure to Reduce Flood Risk and Water Importation

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Abstract:

Green infrastructure (GI) is being implemented in many cities to ameliorate water quantity, water quality, heat island, and other environmental impacts of urbanization. Here we will share applied work on understanding the properties of GI in cities with an emphasis on in situ performance. We will also present results from modeling. We have conducted widespread characterization of bioswale systems in the semi-arid city of Tucson, Arizona. In these studies we have characterized soil organic matter, biogeochemical response, and soil hydraulic properties. Our results from field observations are as follows:

• First, green infrastructure caused increased soil organic matter, 8-10% content versus 1-2% in nearby untreated soils.
• Second, GI soils have increased water holding capacity, 40-60% in green infrastructure soils versus 25-35% in untreated soils.
• Third, GI soils have higher hydraulic conductivity and lower bulk density than nearby untreated soils.
• Fourth, the effect on hydraulic conductivity is uneven. Hydraulic conductivity is often lower in soils with little to no mulch as fine sediments appear to clog the surface.

Additionally, maintenance practices have an effect on infiltration rates. Somewhat unexpectedly soils that are maintained closer to standard landscape aesthetic standards led to lower infiltration rates versus systems that were described as poorly maintained likely due to maintenance resulting in reduced soil organic matter. In runoff observation and modeling studies current rates of deployment do not have a large impact on watershed runoff. However, increased deployment could result in significant water captured for vegetation and reduced flood risk. The effect would vary based on deployment levels, but even modest increases in GI implementation would result in more canopy and reduced risk of floods.

Maricopa County ALERT — Real-time Flood Warning System, Long-term Science Project, or Both?

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The Flood Control District of Maricopa County operates a 24-hour rain, stream, and weather monitoring system known as an ALERT System. ALERT is an acronym for "Automated Local Evaluation in Real Time", and was developed by the National Weather Service in the 1970s. A network of automated data-collection stations is installed in Maricopa and surrounding counties to monitor rainfall and weather, predict the timing and magnitude of floods, and monitor the performance of flood control structures. The presentation will include the history of the ALERT System and its growth from a detection system to a complete warning program that serves County Departments and local emergency responders. Over the 40 years of its existence much data has been collected and stored that can be tapped by the scientific community via the internet. Uses for this data include rainfall and streamflow frequency analysis, historic trends in storm coverage, volume and intensity, effects of urbanization, and the interaction of surface and groundwater during flood events. Examples will be presented in an effort to stimulate the audience into applying this data to their own research and projects.

Forecasting Ridging Related to Precipitation Deficits in Colorado River Basin

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Abstract:

Ridging events are large-scale persistent high pressure systems associated with warm temperatures, clear skies and a general lack of precipitation. When persistent ridging sets up in the right location, atmospheric rivers and precipitation-bearing systems are often diverted northward starving the Western and Southwestern US of a vital source of winter precipitation. As such, in certain water years where ridging is abnormally persistent and frequent (e.g., the notable 2013/2014 winter) the risk of widespread drought heavily increases. Through a research collaboration between NASA-JPL, CW3E, and the California Department of Water Resources, a ridge detection algorithm has recently been developed to objectively track and characterize these ridging events. The ridge detection algorithm tracks ridges with respect to three main locations, with the particular positioning of the ridge centre imposing different regional impacts on the likelihood of wet/dry conditions across the Western and Southwestern US.

This talk focuses on one particular flavor of ridging centered over the Southwest that is most strongly related to dry conditions across the Colorado River Basin. This particular ridge type will be discussed both in terms of subseasonal-to-seasonal (S2S) prediction skill and in terms of longer term trends and the potential role of climate change. In an S2S context, past predictions (i.e., hindcasts) from state-of-the-art numerical weather prediction models are assessed in terms of skill at correctly predicting certain aspects of ridging up to 6-weeks lead time. Efforts to extend the skill at predicting ridging into the seasonal timeframe are ongoing, including testing a variety of machine learning and statistical post-processing approaches. In a climate change context, recent observed trends and climate model experiments are analyzed to investigate whether anthropogenic forcing has already begun to impact ridging in this region.

Increasing Managed Aquifer Recharge of Stormwater with Forecast Informed Reservoir Operations (FIRO)

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Storm water is an important source of water supply to the Orange County groundwater basin. Since Prado Dam was constructed by the US Army Corps of Engineers (USACE) in 1941, OCWD and USACE have worked together to maximize capture of storm water behind the dam. To increase the efficiency of storm water capture at Prado Dam, OCWD is looking to see if Forecast Informed Reservoir Operations (FIRO) can be applied to the Santa Ana River watershed. FIRO uses the most recent developments in weather and climate science to better inform how reservoirs are managed for flood risk management and water supply.

The concept is that FIRO would provide tools to USACE reservoir operators to increase the temporary impoundment of water in the reservoir above the current limit of 20,000 acre-feet (elevation 505 ft msl) without impacting flood risk management. The potential benefit of increasing the level of impoundment was estimated using OCWD's Recharge Facilities Model (RFM), which simulates the operation of Prado Dam and OCWD's surface water recharge system using GoldSim software.

The RFM estimated the additional recharge obtained assuming the level of impoundment behind Prado Dam could be increased to higher elevations ranging from 508 ft msl (25,000 acre-feet of storage) to 517 ft msl (48,800 acre-feet of storage). A projected level of inflow to Prado Dam using current land use and wastewater discharges combined with historical precipitation from 1966-99 was used. At the potential maximum level of impoundment, 517 ft msl, the estimated additional recharge is nearly 8,000 acre-feet per year. The value of this water is over $8M/yr in that it offsets the need to purchase expensive imported water. Increased stormwater recharge also reduces greenhouse gas emissions. The RFM does not take into account other factors that need to be considered, such as forecast uncertainties, flood risk management, environmental impacts, impacts to infrastructure, etc.

Flood-MAR — A California Climate Change Adaptation Strategy

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Abstract:

Severely depleted groundwater aquifers are making groundwater resources unsustainable; causing land subsidence; impacting drinking water quality and availability, agricultural operations, ecosystems, and regional economies; and reducing reserves for drought years. Climate change will cause loss of snowpack, increased inter- and intra-annual variability in precipitation, and more severe flooding and extended droughts adding to challenges for water supply reliability.

Using flood flows for managed aquifer recharge (Flood-MAR) would provide flexibility to the water resources management system to compensate for earlier snow melt runoff, increased variability in precipitation, and expected changes in water demand due to increased temperatures. Flood-MAR integrates flood and groundwater management and could provide multiple benefits, including improved sustainability of groundwater resources, water supply reliability, flood risk reduction, ecosystem enhancement, subsidence mitigation, water quality improvement, agricultural land and open space preservation, and climate change adaptation.

The California Department of Water Resources (DWR), using the decision-scaling methodology, is conducting a climate change vulnerability analysis of the Merced River and the Tuolumne River watersheds. DWR is also exploring the feasibility and effectiveness of Flood-MAR in the Merced River basin using an integrated set of models covering headwaters to groundwater. Initial results show that implementing Flood-MAR projects in the Merced River watershed would provide significant benefits.

Enhancing Hydrometeorlogical Observing Systems throughout California

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The Center for Western Weather and Water Extremes (CW3E), under the umbrella of multiple projects including Forecast Informed Reservoir Operations (FIRO), has been partnering with the US Army Corps of Engineers, the California Department of Water Resources, Sonoma Water, Orange County Water District, Yuba Water Agency, and others to enhance hydrometeorological observing systems throughout California.

FIRO is a proposed management strategy that uses data from watershed monitoring and modern weather and water forecasting to help water managers selectively retain or release water from reservoirs in a manner that reflects current and forecasted conditions. A fundamental focus of FIRO in reservoirs throughout California and western North America is to understand and better predict Atmospheric Rivers (ARs), which provide the majority of California's annual precipitation and cause most of the flood events. To support FIRO objectives, field campaigns have been conducted each winter since 2016, with targeted observations during AR storms and additional continuous long-term observations installed each year to improve the baseline monitoring capabilities in study watersheds.

This presentation will provide an overview of the monitoring enhancements in support of FIRO, including offshore measurements of the atmosphere and ocean, and onshore measurements of the atmosphere and land. In addition, selected results will be presented highlighting advances in process-based understanding and improvements in forecast accuracy made possible with these observations.

Seasonal Streamflow Forecasting in Central Arizona: Recent Improvements and Future Opportunities

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Accurate streamflow forecasts on the Salt-Verde basin that inform reservoir operations are key to striking a balance between water conservation and flood control. Antecedent weather, current snowpack conditions and weather forecasts are the most important sources of streamflow forecast skill. Recent improvements in distributed estimates of snowpack on the Salt-Verde increase skill relative to point observations. Weather forecasts lack skill beyond two-week lead times which limits their utility for seasonal streamflow forecasting. However, increased attention to improving sub-seasonal and seasonal weather forecasts by the scientific community gives hope for improved forecasts in the near future. Small increases in skill can be highly valuable for water supply resiliency but the risks from weather forecast error need to be assessed.

Challenges of Drought Monitoring in Southwest

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Much of the southwest is sparsely inhabited, so ground truth of precipitation events can be hard to come by. Both manual and automated gauges are scarce, but rarely is precipitation evenly distributed in the southwest. Even when rain or snow falls, totals seldom tell the story of whether the precipitation was effective in alleviating drought conditions.

In Arizona we depend on impact reporting to assess how drought conditions have changed. Since drought is not a short-term phenomenon in the west, continual assessment is required from various agencies that have eyes in the field. Mechanisms to simplify the reporting have proven difficult.

The Drought Technical Monitoring Committee, which is part of the Arizona State Drought Task Force, uses a combination of objective gridded data products for various time intervals including % normal precipitation, temperature, Standardized Precipitation Index (SPI), Standardized Precipitation Evaporative Index (SPEI), Vegetation Drought Response Index (VegDRI), and soil moisture to assess both short- and long-term drought conditions. The members of the Committee include the four National Weather Service (NWS) offices that cover Arizona, Arizona State Climatologist, Arizona-based Natural Resource Conservation Service (NRCS) and United States Geological Survey (USGS) staff, Arizona Fish and Game, State Forestry, Department of Water Resources, Salt River Project, University of Arizona Extension Climatologist, the Regional Integrated Science Assessment (RISA) for the Southwest CLIMAS, and Navajo Nation Department of Natural Resources personnel. The consensus of the data is then considered by numerous stakeholders in the region to balance against the impacts being experienced in the region.

With significant rangeland across the southwest, timing of precipitation is as critical as amounts.

Improving Winter Season Precipitation Forecasts Across the Western States

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Monthly tropical sea surface temperature (SST) data are used as predictors to make statistical forecasts of cold season (November-March) precipitation. Through the use of a "combined-lead sea surface temperature" (CLSST) model, predictive information is discovered not just in recent SSTs but also from SSTs up to 18 months prior. We find that CLSST cold season forecast anomaly correlation skill for precipitation is higher than that of the North American Multi-Model Ensemble (NMME) and the SEAS5 model from the European Centre for Medium-Range Weather Forecasts (ECMWF) when averaged over the US. The forecast skill obtained by CLSST in parts of the Intermountain West is of particular interest because of its implications for water resources. In those regions, CLSST dramatically improves the skill over that of the dynamical model ensembles, which can be attributed to a robust statistical response of precipitation in this region to SST anomalies from the previous year in the tropical Pacific.

NASA Western Water Applications in Colorado River Basin: Engaging with Stakeholders to Create Solutions

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The mission of NASA's Western Water Applications Office (WWAO) is to help solve important and pressing water-resource problems that the western United States faces today. To do this, WWAO equips water decision-makers with useful, accessible and sustained remote-sensing-based information. NASA offers unique capabilities that can be used to provide actionable information about water availability, extreme events such as flooding and drought, water quality, user demand, and infrastructure integrity.

Many water managers recognize the value of NASA's data to decision support but they also find it challenging to use the data operationally. In many cases, water managers lack the scientific and technical resources to access, process, or analyze the information for decision making.

WWAO was created to address these challenges and accelerate the application of NASA observations and scientific analysis techniques to tangible, important, and timely water problems. It arms water stakeholders with valuable scientific resources about the changing hydrology of the American west, thus helping them to make better, more informed decisions.

WWAO's approach is to identify stakeholder needs, build projects tailored to meet those needs, engaging with partner from start to finish, and help transition water applications and technology in an operational, sustainable state for long-term impact. After providing an overview of WWAO and the process, we will highlight several projects relevant to the Colorado River Basin and adjacent areas that demonstrate the process at work, from those in development to ones that are underway and those that are in the research-to-operations transition phase. We will also discuss examples of partnerships and relationship building as part of WWAO's approach to meeting its mission.

Mechanisms Driving Cool Season Precipitation Variability in Upper Colorado River Basin

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Water supply to metropolitan areas in seven states rely on snowpack in the upper Colorado River basin (UCRB). Seasonal prediction of snowpack in the UCRB is difficult because the difference between a wet and a dry cool season is often the presence or lack of a few large accumulating events. Atmospheric rivers (ARs) are the dominant mechanism of precipitation variability, with the number of ARs crossing ~32° latitude accounting for ~64% of the interannual variability of winter precipitation in the UCRB. There may be some skill in seasonal prediction of UCRB snowpack, as AR frequency is tied to tropical ocean temperature at various lag times. Because ARs are responsible for many of the large snowfall accumulation events in the UCRB, in this presentation, I will discuss characteristics of ARs that influence precipitation amount in the UCRB.

On the other hand, predicting conditions that hinder large accumulation events may be equally important in forecasting Colorado River yield. Amplified ridge conditions over western North America block systems that bring snowpack to the region, and are somewhat predictable on sub-seasonal timescales. In addition to precipitation, temperature is an important control on runoff.

The purpose of this presentation is to discuss the characteristics and prediction potential of these and other mechanisms that produce large accumulating events, as well as to make recommendations for improving Colorado River yield prediction.