Climate modeling 101: Explanations without equations

Springer | January 1st, 2016

Climate scientists tell us it's going to get hotter. How much it rains and where it rains is likely to shift. Sea level rise is apt to accelerate. Oceans are on their way

Climate scientists tell us it's going to get hotter. How much it rains and where it rains is likely to shift. Sea level rise is apt to accelerate. Oceans are on their way to becoming more acidic and less oxygenated. Floods, droughts, storms, and other extreme weather events are projected to change in frequency or intensity. But how do they know what they know? For climate scientists, numerical models are the tools of the trade. But for the layperson — and even for scientists in other fields — climate models can seem mysterious. What does "numerical" even mean? Do climate models take other things besides the atmosphere into account? How do scientists know if a model is any good? * Two experts in climate modeling, Andrew Gettelman of the National Center for Atmospheric Research and Richard Rood of the University of Michigan, have your answers and more, free of charge. In a new open-access book, "Demystifying Climate Models," the pair lay out the fundamentals. In 282 pages, the scientists explain the basics of climate science, how that science is translated into a climate model, and what those models can tell us (as well as what they can't) — all without using a single equation. *Find the answers on pages 8, 13, and 161, respectively, of the book.

Climate Risk-Informed Flood Inundation Mapping (CRFM) Project

California Department of Water Resources (DWR) | May 1st, 2025

The California Department of Water Resources (DWR) has identified the enhancement of flood inundation mapping under future climate conditions as a fundamental and critica

The California Department of Water Resources (DWR) has identified the enhancement of flood inundation mapping under future climate conditions as a fundamental and critical climate change adaptation strategy. Mapping serves as foundational information upon which future planning and actions depend — necessary, though insufficient, for climate resilience. This innovative study focuses on the Tuolumne River and leverages existing studies’ models, data, and tools to pioneer a risk-informed approach in creating a flood inundation mapping procedure that supports climate resilience. This study moves beyond outdated stationarity-based practices by incorporating non-stationarity into climate change projections, offering a forward-thinking solution to address the limitations of current methodologies.

Climate Warming and Water Management Adaptation for California

Climatic Change (Springer) | June 10th, 2010

The ability of California’s water supply system to adapt to long-term climatic and demographic changes is examined. Two climate warming and a historical climate

The ability of California’s water supply system to adapt to long-term climatic and demographic changes is examined. Two climate warming and a historical climate scenario are examined with population and land use estimates for the year 2100 using a statewide economic-engineering optimization model of water supply management. Methodologically, the results of this analysis indicate that for long-term climate change studies of complex systems, there is considerable value in including other major changes expected during a long-term time-frame (such as population changes), allowing the system to adapt to changes in conditions (a common feature of human societies), and representing the system in sufficient hydrologic and operational detail and breadth to allow significant adaptation. While the policy results of this study are preliminary, they point to a considerable engineering and economic ability of complex, diverse, and intertied systems to adapt to significant changes in climate and population. More specifically, California’s water supply system appears physically capable of adapting to significant changes in climate and population, albeit at a significant cost. Such adaptation would entail large changes in the operation of California’s large groundwater storage capacity, significant transfers of water among water users, and some adoption of new technologies.

Climate warming enhancement of catastrophic southern California debris flows

Nature Portfolio (Springer Nature) | June 29th, 2020

The sequence of wildfires followed by debris flows, frequently affects southern California, reflecting its drought-heavy precipitation climate bipolarity. Organic debris

The sequence of wildfires followed by debris flows, frequently affects southern California, reflecting its drought-heavy precipitation climate bipolarity. Organic debris from incomplete burning is lighter than inorganic matter, and partially inviscid. Hence lower rainfall totals can trigger downslope motion than typically required by the underlying clasts of loose inorganic granular material. After advection downslope, the pebble-laden organic debris has a higher capacity for rilling; a positive feedback process. A mechanism is proposed whereby boulders are ‘rafted’ by organic debris. This coordinated movement of boulders greatly enhances the debris flow erosion capacity. This climate change sensitive debris flow enhancing mechanism, through organic–inorganic granular material interaction, is supported by observations and the numerical simulations. Using a model explicitly parameterizing erosion processes, including runoff entrainment, rilling incision, and bank collapse, the lifecycle of the Montecito debris flow of January 9, 2018 is simulated, providing quantitative estimates of mass conveyed and debris sorting at the terminus. Peak rafting speeds are ~ 12.9 m/s at ~ 300 m asl. Total boulder (effective diameter > 25 cm) volume involved for the Ysidro Creek area alone is ~ 5 × 104 m3, scattered between the region 50–260 m asl. Debris flows are highly repeatable and locations prone to debris flows are identified and their likelihood of realization estimated.

Climate, Drought, and Sea Level Rise Scenarios for the Fourth California Climate Assessment

California Energy Commission (CEC) | August 27th, 2018

Daily temperature and precipitation over California at a resolution of 1/16° (about 6 km, or 3.7 miles) were generated to support climate change impact studies for the

Daily temperature and precipitation over California at a resolution of 1/16° (about 6 km, or 3.7 miles) were generated to support climate change impact studies for the energy system and other sectors featured in the California’s Fourth Climate Change Assessment. The data, derived from 32 coarse-resolution (~ 100 km) global climate models (GCMs), were bias corrected and downscaled using the Localized Constructed Analogues (LOCA) statistical method. The data cover 1950-2005 for the historical period and 2006-2100 for two future climate projections using medium and high greenhouse gas and aerosol emissions scenarios. Statewide, temperature is projected to increase 2-4 °C (medium emissions scenario) to 4-7 °C (high emissions scenario) by the end of this century. Precipitation shows fewer wet days, wetter winters, drier springs and autumns, and an increase in dry years as well as maximum precipitation in a single day. Ten GCMs that closely simulate California’s climate are identified for studies where all 32 GCMs cannot be used. Additional variables were downscaled for these 10, including wind speed, specific and relative humidity, and surface solar radiation. Four models that span the temperature and precipitation changes from the 10 are identified for studies that cannot accommodate the 10. Wind speed shows small decreases, while relative humidity changes are more complicated, with coastal increases but decreases inland. Surface solar radiation shows small Southern California increases in spring. The downscaled fields were applied to the Variable Infiltration Capacity (VIC) land surface model to develop snow cover, soil moisture, runoff, water loss from plants, surface heat fluxes, and other parameters. Moisture deficit is projected to increase over much of the state, particularly Northern California and the Sierra Nevada, while top level soil moisture is projected to decrease, particularly in Southern California. Most streamflows shift to earlier in the year, with the bigger shifts experienced in basins which currently have substantial contributions from snowmelt. Two versions of a 20-year dry spell were identified from one of the GCM simulations to investigate future drought: the original episode from 2051-2070, and one shifted earlier in the century with temperatures consistent with 2023-2042. For both, we provide downscaled temperatures and precipitation along with VIC hydrological output. Sea level rise (SLR) projections for California were generated using a probabilistic approach employing estimates of the components that contribute to global and regional SLR, including new science on the possibility of increased contribution from Antarctica. Hourly projections of sea level at selected coastal locations were generated out to 2100 that include tides, regional and local weather influences, and short period Pacific climate fluctuations along with the aforementioned sea level rise scenarios. The climate scenario and SLR data are available online from cal-adapt.org.

Co-producing actionable science for water utilities

Climate Services (Elsevier) | July 7th, 2016

This article explores the efforts of four water utilities to co-produce actionable science by forging partnerships with scientific institutions to explore integrating cl

This article explores the efforts of four water utilities to co-produce actionable science by forging partnerships with scientific institutions to explore integrating climate considerations into their specific management context. The experiences of these four utilities and their scientific partners, as part of the Piloting Utility Modeling Applications project of the Water Utility Climate Alliance, provide a wealth of empirical evidence to illustrate some of the core concepts formulated to explain how to produce usable information and how to link research to decision making. Through these four case studies of co-production, we identify three findings that bridge principles and practice: each utility engaged in contextualizing research; in building and leveraging knowledge networks; and in embracing an entrepreneurial approach to their research agenda. In several instances, unanticipated but innovative assessment techniques were developed by science partners in collaboration with water utilities to fit the utility’s specific needs. The paper concludes by discussing some of the hard realities of co-production illustrated by these cases that should be kept in mind by people contemplating similar projects.

Colorado River Basin Climate and Hydrology State of the Science

University of Colorado, Boulder | April 15th, 2020

The Colorado River Basin currently faces unprecedented stresses. Persistent dry conditions since 2000, along with the increasing recognition that warming temperatures are

The Colorado River Basin currently faces unprecedented stresses. Persistent dry conditions since 2000, along with the increasing recognition that warming temperatures are impacting the hydrology of the basin, have led to great concerns about the long-term reliability of basin water supplies. With ever-higher stakes for water resource planning and decision making, an even greater emphasis is placed on the tools that support those activities, notably Reclamation’s operations and planning models and similar models used at other agencies. The usefulness of these system models depends on many types of datasets and forecasts that serve as inputs to them, as well as the research and scientific understanding underpinning this complex chain of data and models. The development and refinement of the different links of the chain necessarily involves researchers, forecasters, and water managers. New research efforts have advanced our understanding of the hydroclimate of the basin and how key hydroclimate processes, variability, and changes can be captured in data and models. This rapid expansion of the scientific knowledge base, and the increasing complexity of the data and models used to operationalize that knowledge, parallel the growing uncertainties about the future climate and hydrology. Accordingly, basin stakeholders have recognized the importance of reassessing the scientific and technical basis for management and planning.

Colorado River water supply is predictable on multi-year timescales owing to long-term ocean memory

Nature Portfolio (Springer Nature) | October 9th, 2020

Skillful multi-year climate forecasts provide crucial information for decision-makers and resource managers to mitigate water scarcity, yet such forecasts remain challen

Skillful multi-year climate forecasts provide crucial information for decision-makers and resource managers to mitigate water scarcity, yet such forecasts remain challenging due to unpredictable weather noise and the lack of dynamical model capability. Here we demonstrate that the annual water supply of the Colorado River is predictable up to several years in advance by a drift-free decadal climate prediction system using a fully coupled climate model. Observational analyses and model experiments show that prolonged shortages of water supply in the Colorado River are significantly linked to sea surface temperature precursors including tropical Pacific cooling, North Pacific warming, and southern tropical Atlantic warming. In the Colorado River basin, the water deficits can reduce crop yield and increase wildfire potential. Thus, a multi-year prediction of severe water shortages in the Colorado River basin could be useful as an early indicator of subsequent agricultural loss and wildfire risk.

Combined Modeling of US Fluvial, Pluvial, and Coastal Flood Hazard Under Current and Future Climates

American Geophysical Union (AGU) | December 16th, 2020

Comparison of potential drinking water source contamination across one hundred U.S. cities

Nature Portfolio (Springer Nature) | December 13th, 2021

Drinking water supplies of cities are exposed to potential contamination arising from land use and other anthropogenic activities in local and distal source watersheds. B

Drinking water supplies of cities are exposed to potential contamination arising from land use and other anthropogenic activities in local and distal source watersheds. Because water quality sampling surveys are often piecemeal, regionally inconsistent, and incomplete with respect to unregulated contaminants, the United States lacks a detailed comparison of potential source water contamination across all of its large cities. Here we combine national scale geospatial datasets with hydrologic simulations to compute two metrics representing potential contamination of water supplies from point and nonpoint sources for over a hundred U.S. cities. We reveal enormous diversity in anthropogenic activities across watersheds with corresponding disparities in the potential contamination of drinking water supplies to cities. Approximately 5% of large cities rely on water that is composed primarily of runoff from non-pristine lands (e.g., agriculture, residential, industrial), while four-fifths of all large cities that withdraw surface water are exposed to treated wastewater in their supplies.