Preparing for climate change in Washington State

Climate change is expected to bring potentially significant changes to Washington State’s natural, institutional, cultural, and economic landscape. Addressing climate change impacts will require a sustained commitment to integrating climate information into the day-to-day governance and management of infrastructure, programs, and services that may be affected by climate change. This paper discusses fundamental concepts for planning for climate change and identifies options for adapting to the climate impacts evaluated in the Washington Climate Change Impacts Assessment. Additionally, the paper highlights potential avenues for increasing flexibility in the policies and regulations used to govern human and natural systems in Washington.     

δ53Cr values of catchment runoff exhibit seasonality regardless of bedrock Cr concentrations: Role of periodically changing chromium export fluxes

One pre-requisite for the construction of a global chromium isotope mass balance is detailed understanding of Cr isotope systematics in the critical zone where redox-processes can modify the isotope signature of geogenic Cr input into the hydrosphere. A Cr isotope inventory of bedrock, soil, and runoff was performed in a Central European headwater catchment underlain by amphibolite, situated in the vicinity of two previously studied catchments underlain by different bedrock types (serpentinite and leucogranite). Fresh bedrock in the amphibolite catchment NAZ contained ~300 mg/kg Cr, serpentinite at PLB contained ~800 mg/kg Cr, and leucogranite at LYS contained ~2 mg/kg Cr. Monthly hydrochemical monitoring at all three sites revealed higher Cr(VI) export fluxes in winter than in summer. NAZ was characterized by a distinct seasonality in the δ⁵³Cr values, with minima during winter/spring snowmelts (−0.35‰) and maxima during dry summers (0.40‰). Similar seasonality in δ⁵³Cr values had been reported from PLB and LYS. Bedrock at all three sites had similar Cr isotope composition close to −0.10‰, a value indistinguishable from the δ⁵³Cr value of bulk silicate Earth (BSE). Positive mean δ⁵³Cr value of NAZ runoff indicated Cr-isotope fractionations during weathering of geogenic Cr(III), combined with adsorption of the resulting Cr(VI) on soil particles during pedogenesis. However, the mass-weighted mean δ⁵³Cr of NAZ runoff was lower (−0.08‰), indistinguishable from the Cr isotope signature of bedrock. The same pattern of lower mass-weighted mean δ⁵³Cr values of runoff, compared to arithmetic mean δ⁵³Cr values of runoff, were observed also at PLB and LYS. We suggest that elevated Cr runoff fluxes in winter remove some of the residual isotopically light Cr that accumulated in the soil during summer. Seasonality in runoff δ⁵³Cr values appears to be a relatively widespread phenomenon, de-coupled from Cr availability for chemical weathering.     

Effects of projected climate change on energy supply and demand in the Pacific Northwest and Washington State

Climate strongly affects energy supply and demand in the Pacific Northwest (PNW) and Washington State (WA). We evaluate potential effects of climate change on the seasonality and annual amount of PNW hydropower production, and on heating and cooling energy demand. Changes in hydropower production are estimated by linking simulated streamflow scenarios produced by a hydrology model to a simulation model of the Columbia River hydro system. Changes in energy demand are assessed using gridded estimates of heating degree days (HDD) and cooling degree days (CDD) which are then combined with population projections to create energy demand indices that respond both to climate, future population, and changes in residential air conditioning market penetration. We find that substantial changes in the amount and seasonality of energy supply and demand in the PNW are likely to occur over the next century in response to warming, precipitation changes, and population growth. By the 2040s hydropower production is projected to increase by 4.7–5.0% in winter, decrease by about 12.1–15.4% in summer, with annual reductions of 2.0–3.4%. Larger decreases of 17.1–20.8% in summer hydropower production are projected for the 2080s. Although the combined effects of population growth and warming are projected to increase heating energy demand overall (22–23% for the 2020s, 35–42% for the 2040s, and 56–74% for the 2080s), warming results in reduced per capita heating demand. Residential cooling energy demand (currently less than one percent of residential demand) increases rapidly (both overall and per capita) to 4.8–9.1% of the total demand by the 2080s due to increasing population, cooling degree days, and air conditioning penetration.     

Assessing regional impacts and adaptation strategies for climate change: the Washington Climate Change Impacts Assessment

Climate change in the twenty-first century will strongly affect the processes that define natural and human systems. The Washington Climate Change Impacts Assessment (WACCIA) was intended to identify the nature and effects of climate change on natural and human resources in Washington State over the next century. The assessment focused on eight sectors that were identified as being potentially most climate sensitive: agriculture, energy, salmon, urban stormwater infrastructure, forests, human health, coasts, and water resources. Most of these sectors are sensitive in one way or another to water availability. While water is generally abundant in the state under current climate conditions, its availability is highly variable in space and time, and these variations are expected to change as the climate warms. Here we summarize the results of the WACCIA and identify uncertainties and common mechanisms that relate many of the impacts. We also address cross-sectoral sensitivities, vulnerabilities, and adaptation strategies.     

Time-series of δ26Mg values in a headwater catchment reveal decreasing magnesium isotope variability from precipitation to runoff

Data on temporal variability in Mg isotope ratios of atmospheric deposition and runoff are critical for decreasing the uncertainty associated with construction of isotope mass balances in headwater catchments, and statistical evaluation of isotope differences among Mg pools and fluxes. Such evaluations, in turn, are needed to distinguish between biotic and abiotic contributions to Mg²⁺ in catchment runoff. We report the first annual time-series of δ²⁶Mg values simultaneously determined for rainfall, canopy throughfall, soil water and runoff. The studied 55-ha catchment, situated in western Czech Republic, is underlain by Mg-rich amphibolite and covered by mature spruce stands. Between 1970 and 1996, the site received extremely high amounts of acid deposition and fly ash form nearby coal-burning power plants. The δ²⁶Mg values of open-area precipitation (median of −0.79‰) at our study site were statistically indistinguishable from the δ²⁶Mg values of throughfall (−0.73‰), but significantly different from the δ²⁶Mg values of soil water (−0.55‰) and runoff (−0.55‰). The range of δ²⁶Mg values during the observation period decreased in the order: open-area precipitation (0.57‰) > throughfall (0.27‰) > runoff (0.21‰) > soil water (0.16‰). The decreasing variability in δ²⁶Mg values of Mg²⁺ from precipitation to soil water and runoff reflected an increasing homogenization of atmospheric Mg in the catchment and its mixing with geogenic Mg. In addition to atmospheric Mg, runoff also contained Mg mobilized from the three major solid Mg pools, bedrock (δ²⁶Mg of −0.32‰), soil (−0.28‰), and vegetation (−0.31‰). The drought of summer 2019 did not affect the nearly constant δ²⁶Mg value of runoff. Collectively, our data show that within-catchment processes buffer the Mg isotope variability of the atmospheric input.     

Comparison of geostatistical approaches dealing with the distribution of snow

This paper deals with a stochastic simulation. Snow cover, representing a regionalized variable, was studied and used as an input parameter for a stochastic simulation. The first step included basic statistical analysis of individual parameters of snow, e.g. snow height. In the next step, an analysis of relationships between the snow and the geomorphological parameters (altitude, slope and aspect) was conducted. The most current methods of spatial interpolation and multifactor evaluation are based on weighted regression relationships. Primarily, the use of conditional stochastic simulation was tested in a variety of software. The main aim of this investigation is to compare selected interpolation methods with stochastic simulation, based on the development of the values and on the evaluation of the incidence of extreme events. The study shall provide users with recommendations for selecting the optimal interpolation method and its application to real data.     

Climate change impacts on water management and irrigated agriculture in the Yakima River Basin, Washington, USA

The Yakima River Reservoir system supplies water to ~180,000 irrigated hectares through the operation of five reservoirs with cumulative storage of ~30% mean annual river flow. Runoff is derived mostly from winter precipitation in the Cascade Mountains, much of which is stored as snowpack. Climate change is expected to result in earlier snowmelt runoff and reduced summer flows. Effects of these changes on irrigated agriculture were simulated using a reservoir system model coupled to a hydrological model driven by downscaled scenarios from 20 climate models archived by the 2007 Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report. We find earlier snowmelt results in increased water delivery curtailments. Historically, the basin experienced substantial water shortages in 14% of years. Without adaptations, for IPCC A1B global emission scenarios, water shortages increase to 27% (13% to 49% range) in the 2020s, to 33% in the 2040s, and 68% in the 2080s. For IPCC B1 emissions scenarios, shortages occur in 24% (7% to 54%) of years in the 2020s, 31% in the 2040s and 43% in the 2080s. Historically unprecedented conditions where senior water rights holders suffer shortfalls occur with increasing frequency in both A1B and B1 scenarios. Economic losses include expected annual production declines of 5%–16%, with greater probabilities of operating losses for junior water rights holders.     

Forest ecosystems, disturbance, and climatic change in Washington State, USA

Climatic change is likely to affect Pacific Northwest (PNW) forests in several important ways. In this paper, we address the role of climate in four forest ecosystem processes and project the effects of future climatic change on these processes across Washington State. First, we relate Douglas-fir growth to climatic limitation and suggest that where Douglas-fir is currently water-limited, growth is likely to decline due to increased summer water deficit. Second, we use existing analyses of climatic controls on tree species biogeography to demonstrate that by the mid twenty-first century, climate will be less suitable for key species in some areas of Washington. Third, we examine the relationships between climate and the area burned by fire and project climatically driven regional and sub-regional increases in area burned. Fourth, we suggest that climatic change influences mountain pine beetle (MPB) outbreaks by increasing host-tree vulnerability and by shifting the region of climate suitability upward in elevation. The increased rates of disturbance by fire and mountain pine beetle are likely to be more significant agents of changes in forests in the twenty-first century than species turnover or declines in productivity, suggesting that understanding future disturbance regimes is critical for successful adaptation to climate change.     

Assessing DOC export from a Sphagnum‐dominated peatland using δ13C and δ18O–H2O stable isotopes

Dissolved organic carbon (DOC) originating in peatlands can be mineralized to carbon dioxide (CO₂) and methane (CH₄), two potent greenhouse gases. Knowledge of the dynamics of DOC export via run‐off is needed for a more robust quantification of C cycling in peatland ecosystems, a prerequisite for realistic predictions of future climate change. We studied dispersion pathways of DOC in a mountain‐top peat bog in the Czech Republic (Central Europe), using a dual isotope approach. Although δ¹³C_DOC values made it possible to link exported DOC with its within‐bog source, δ¹⁸O_H2O values of precipitation and run‐off helped to understand run‐off generation. Our 2‐year DOC–H₂O isotope monitoring was complemented by a laboratory peat incubation study generating an experimental time series of δ¹³C_DOC values. DOC concentrations in run‐off during high‐flow periods were 20–30 mg L^?1. The top 2 cm of the peat profile, composed of decaying green moss, contained isotopically lighter C than deeper peat, and this isotopically light C was present in run‐off in high‐flow periods. In contrast, baseflow contained only 2–10 mg DOC L^?1, and its more variable C isotope composition intermittently fingerprinted deeper peat. DOC in run‐off occasionally contained isotopically extremely light C whose source in solid peat substrate was not identified. Pre‐event water made up on average 60% of the water run‐off flux, whereas direct precipitation contributed 40%. Run‐off response to precipitation was relatively fast. A highly leached horizon was identified in shallow catotelm. This peat layer was likely affected by a lateral influx of precipitation. Within 36 days of laboratory incubation, isotopically heavy DOC that had been initially released from the peat was replaced by isotopically lighter DOC, whose δ¹³C values converged to the solid substrate and natural run‐off. We suggest that δ¹³C systematics can be useful in identification of vertically stratified within‐bog DOC sources for peatland run‐off.     

Implications of 21st century climate change for the hydrology of Washington State

Pacific Northwest (PNW) hydrology is particularly sensitive to changes in climate because snowmelt dominates seasonal runoff, and temperature changes impact the rain/snow balance. Based on results from the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR4), we updated previous studies of implications of climate change on PNW hydrology. PNW 21st century hydrology was simulated using 20 Global Climate Models (GCMs) and 2 greenhouse gas emissions scenarios over Washington and the greater Columbia River watershed, with additional focus on the Yakima River watershed and the Puget Sound which are particularly sensitive to climate change. We evaluated projected changes in snow water equivalent (SWE), soil moisture, runoff, and streamflow for A1B and B1 emissions scenarios for the 2020s, 2040s, and 2080s. April 1 SWE is projected to decrease by approximately 38–46% by the 2040s (compared with the mean over water years 1917–2006), based on composite scenarios of B1 and A1B, respectively, which represent average effects of all climate models. In three relatively warm transient watersheds west of the Cascade crest, April 1 SWE is projected to almost completely disappear by the 2080s. By the 2080s, seasonal streamflow timing will shift significantly in both snowmelt dominant and rain–snow mixed watersheds. Annual runoff across the State is projected to increase by 2–3% by the 2040s; these changes are mainly driven by projected increases in winter precipitation.