The magnitude and spatial patterns of historical and future hydrologic change in California’s watersheds

Ecological Society of America (ESA) | February 12th, 2015

Process-based models that link climate and hydrology permit improved assessments of climate change impacts among watersheds. We used the Basin Characterization Model (BCM

Process-based models that link climate and hydrology permit improved assessments of climate change impacts among watersheds. We used the Basin Characterization Model (BCM), a regional water balance model to (1) ask what is the magnitude of historical and projected future change in the hydrology of California’s watersheds; (2) test the spatial congruence of watersheds with the most historical and future hydrologic change; and (3) identify watersheds with high levels of hydrologic change under drier and wetter future climates. We assessed change for 5135 watersheds over a 60-year historical period and compared it to 90-year future projections. Watershed change was analyzed for climatic water deficit, April 1st snowpack, recharge, and runoff. Watersheds were ranked by change for the historical and twofuture scenarios. We developed a normalized index of hydrologic change that combined the four variables, and identified which watersheds show the most spatial congruence of large historical change and continued change under the two futures. Of the top 20%of all watersheds (1028), 591 in the Sierra Nevada Mountains and Northwestern eco-regions have high spatial congruence across all time periods. Among watersheds where change accelerates in the future, but not historically, a majority are congruent between both climate models, predominantly in the Sierra Nevada, Cascade Ranges and the Northwestern eco-regions. This congruence of impacts in watersheds under drier or wetter scenarios is driven by snowpack, but in areas with low snowpack, hydrologic change varied spatially depending on projected precipitation and temperature, with 151 watersheds in Northwestern California showing high levels of drying under the drier scenario, while 103 watersheds in Central western and Southwestern California show increasing hydrologic activity under the wetter scenario. In some regions, the loss of snowpack allows the cycle of runoff and recharge to function without delay represented by springtime snow melt, causing these watersheds to become more immediately hydrologically responsive to changing climate. The study also found watersheds with low rainfall that have already passed through their highest response to changing climate, and show less future change. The methods used here can also be used to identify watersheds resilient to changing climate.

The Seasonal Cycle of Surface Soil Moisture

American Meteorological Society (AMS) | June 29th, 2022

The seasonal cycle contributes substantially to soil moisture temporal variability in many parts of the world, with important implications for seasonal forecasting releva

The seasonal cycle contributes substantially to soil moisture temporal variability in many parts of the world, with important implications for seasonal forecasting relevant to agriculture and the health of humans and ecosystems. There is considerable spatial variability in the seasonal cycle of soil moisture, yet a lack of global observations has hindered the development of parsimonious theories explaining that variability. Here, we use 6 years of global satellite observations to describe and explain the seasonal cycle of surface soil moisture globally. An unsupervised clustering algorithm is used to identify five distinct seasonal cycle regimes. Each seasonal cycle regime typically arises in both hemispheres, on multiple continents, and across substantially different local climates. To explain this spatial variability, we then show that the observed seasonal cycle regimes are reproduced very well by a simple but physically based water balance model, which only uses precipitation and downwelling surface shortwave radiation as inputs, and includes no free parameters. Surprisingly, no information on vegetation or land cover is required. To our knowledge, this is the first characterization of the seasonal cycle of surface soil moisture based on global observations.

The unequal burdens of water scarcity

Nature Portfolio (Springer Nature) | January 19th, 2023

Curtailing water use during drought is costly, but those costs are not evenly distributed. Socio–hydrological modelling shows how water burdens fall more heavily on poo

Curtailing water use during drought is costly, but those costs are not evenly distributed. Socio–hydrological modelling shows how water burdens fall more heavily on poor households in response to water conservation policies.

The Uneven Nature of Daily Precipitation and Its Change

American Geophysical Union (AGU) | October 19th, 2018

Rain falls unevenly in time, which can lead to floods and droughts. It is widely known that precipitation is uneven, but it is difficult to quantify. Here we develop a me

Rain falls unevenly in time, which can lead to floods and droughts. It is widely known that precipitation is uneven, but it is difficult to quantify. Here we develop a measure for the unevenness of precipitation: the number of the wettest days each year in which half of the annual rain falls. We apply this to rain observed by gauges around the world. At all gauges combined, it takes only 12 days each year for half of the rain to fall. We also apply the measure to climate model simulations, with projections for the rest of the century. In the climate model simulations, the change in future rainfall is even more uneven than rainfall today: In a scenario with high greenhouse‐gas emissions, half of the increase in rainfall happens in the wettest 6 days each year. Rather than assuming more rain in general, society needs to take measures to deal with little change most of the time and a handful of events with much more rain.

The uneven response of different snow measures to human-induced climate warming

American Meteorological Society (AMS) | June 25th, 2013

The effect of human-induced climate warming on different snow measures in the western United States is compared by calculating the time required to achieve a stat

The effect of human-induced climate warming on different snow measures in the western United States is compared by calculating the time required to achieve a statistically significant linear trend in the different measures, using time series derived from regionally downscaled global climate models. The measures examined include the water content of the spring snowpack, total cold-season snowfall, fraction of winter precipitation that falls as snow, length of the snow season, and fraction of cold-season precipitation retained in the spring snowpack, as well as temperature and precipitation. Various stakeholders may be interested in different sets of these variables. It is found that temperature and the fraction of winter precipitation that falls as snow exhibit significant trends first, followed in 5–10 years by the fraction of cold-season precipitation retained in the spring snowpack, and later still by the water content of the spring snowpack. Change in total cold-season snowfall is least detectable of all the measures, since it is strongly linked to precipitation, which has large natural variability and only a weak anthropogenic trend in the western United States. Averaging over increasingly wider areas monotonically increases the signal-to-noise ratio of the 1950–2025 linear trend from 0.15 to 0.37, depending on the snow measure.

The Use of Smolt Survival Estimates to Quantify the Effects of Habitat Changes on Salmonid Stocks in the Sacramento-San Joaquin Rivers, California

Canada Department of Fisheries and Oceans (DFO) | July 1st, 1989

Three-dimensional geologic mapping of the Cenozoic basin fill, Amargosa Desert basin, Nevada and California

U.S. Geological Survey (USGS) | July 1st, 2014

Understanding the subsurface geologic framework of the Cenozoic basin fill that underlies the Amargosa Desert in southern Nevada and southeastern California has been impr

Understanding the subsurface geologic framework of the Cenozoic basin fill that underlies the Amargosa Desert in southern Nevada and southeastern California has been improved by using borehole data to construct three-dimensional lithologic and interpreted facies models. Lithologic data from 210 boreholes from a 20-kilometer (km) by 90-km area were reduced to a limited suite of descriptors based on geologic knowledge of the basin and distributed in three-dimensional space using interpolation methods. The resulting lithologic model of the Amargosa Desert basin portrays a complex system of interfingered coarse- to fine-grained alluvium, playa and palustrine deposits, eolian sands, and interbedded volcanic units. Lithologic units could not be represented in the model as a stacked stratigraphic sequence due to the complex interfingering of lithologic units and the absence of available time-stratigraphic markers. Instead, lithologic units were grouped into interpreted genetic classes, such as playa or alluvial fan, to create a three-dimensional model of the interpreted facies data. Three-dimensional facies models computed from these data portray the alluvial infilling of a tectonically formed basin with intermittent internal drainage and localized regional groundwater discharge. The lithologic and interpreted facies models compare favorably to resistivity, aeromagnetic, and geologic map data, lending confidence to the interpretation.

Three-Dimensional Hydrogeologic Framework Model of the Russian River Watershed, California

U.S. Geological Survey (USGS) | December 19th, 2024

The U.S. Geological Survey (USGS) was invited by the California State Water Resources Control Board and Sonoma County Water Agency to cooperate on a scientific investigat

The U.S. Geological Survey (USGS) was invited by the California State Water Resources Control Board and Sonoma County Water Agency to cooperate on a scientific investigation to evaluate the groundwater resources of the Russian River watershed and to develop tools to better understand and manage the groundwater system. The purpose of this report is to describe the development of a digital 3D HFM of the Russian River watershed. Such a model will help fully conceptualize the 3D subsurface configuration of aquifers and also may be used as the primary geologic input to numerical simulations of the hydrologic system. The 3D HFM, and data used to construct the 3D HFM, can be found in the following data release (Fenton and others, 2022).

Tools for managing hydrologic alteration on a regional scale II: Setting targets to protect stream health

Freshwater Biology (Wiley) | January 15th, 2018

1. Widespread hydrologic alteration creates a need for tools to assess ecological impacts to streams that can be applied across large geographic scales. A regional framew

1. Widespread hydrologic alteration creates a need for tools to assess ecological impacts to streams that can be applied across large geographic scales. A regional framework for biologically based flow management can help catchment managers prioritise streams for protection, evaluate impacts of disturbance or interventions and provide a starting point for causal assessment in degraded streams. However, lack of flow data limit the ability to assess hydrologic conditions across a region. 2. Hydrologic models can address this problem. Regionally calibrated hydrologic models were used to estimate current and reference flows at 572 bioassessment sites in southern and central coastal California. Flow alteration was characterised as the difference in 39 flow metrics calculated from simulations of present‐day and reference flow time‐series, calculated under up to four precipitation conditions. 3. Biological condition was assessed with the California Stream Condition Index (CSCI) and its components. Logistic regressions were used to predict the likelihood of high scores (i.e. ≥10th percentile of the CSCI reference calibration data). Statistically significant relationships between increasing severity of hydrologic alteration and decreasing biological condition were used to set thresholds that reflected tolerance for risk of a stakeholder advisory group. 4. An index of hydrologic alteration was created by selecting flow metrics based on their importance for predicting biological response variables in boosted regression tree models. Metrics were selected in the order of decreasing importance, and no more than two metrics per metric class were selected (i.e. duration, frequency, magnitude, timing and variability). Seven metrics were selected: HighDur (duration of high‐flow events), HighNum (# of high‐flow events), NoDisturb (duration between high‐ or low‐flow events), MaxMonthQ (maximum monthly discharge), Q99 (99th percentile of daily streamflow), QmaxIDR (interdecile range of annual maxima) and RBI (Richards–Baker Index). 5. Applying the index to data from a probabilistic survey, 34% of stream‐miles in southern California were estimated to be hydrologically altered. One of four management priorities were assigned to each site based on biological condition and hydrologic status: protection (healthy and unaltered, 52% of stream‐miles), monitoring (healthy but altered 4%), evaluation of flow management (unhealthy and altered, 30%) and evaluation of other management (unhealthy but unaltered, 14%). 6. Regionally derived biologically based targets for flow alteration allow catchment managers to prioritise activities and conduct screenings for causal assessments across large spatial scales. Furthermore, regional tools pave the way for incorporation of hydrologic management in policies and catchment planning designed to support biological integrity in streams. Development of regional tools should be a priority where hydrologic alteration is pervasive or expected to increase in response to climate change or urbanisation.

Towards an operational anthropogenic CO2 emissions monitoring and verification support capacity

American Meteorological Society (AMS) | February 10th, 2020

Under the Paris Agreement progress of emission reduction efforts is tracked on the basis of regular updates to national Greenhouse Gas (GHG) inventories, referred to as

Under the Paris Agreement progress of emission reduction efforts is tracked on the basis of regular updates to national Greenhouse Gas (GHG) inventories, referred to as bottom-up estimates. However, only top-down atmospheric measurements can provide observation-based evidence of emission trends. Today there is no internationally agreed, operational capacity to monitor anthropogenic GHG emission trends using atmospheric measurements to complement national bottom-up inventories. The European Commission (EC), the European Space Agency, the European Centre for Medium-Range Weather Forecasts, the European Organisation for the Exploitation of Meteorological Satellites and international experts, are joining forces to develop such an operational capacity for monitoring anthropogenic CO2 emissions as a new CO2 service under EC's Copernicus Programme. Design studies have been used to translate identified needs into defined requirements and functionalities of this anthropogenic CO2 emissions Monitoring and Verification Support (CO2MVS) capacity. It adopts a holistic view and includes components such as atmospheric space-borne and in-situ measurements, bottom up CO2 emission maps, improved modeling of the carbon cycle, an operational data assimilation system integrating top-down and bottom-up information, and a policy-relevant decision support tool. The CO2MVS capacity with operational capabilities by 2026, is expected to visualize regular updates of global CO2 emissions, likely at 0.05°x0.05°. This will complement the PA’s enhanced transparency framework, providing actionable information on anthropogenic CO2 emissions that are the main driver of climate change. This information will be available to all stakeholders, including governments and citizens, allowing them to reflect on trends and effectiveness of reduction measures. The new EC gave green light to pass the CO2MVS from exploratory to implementing phase.