Development of a Continental Scale Water Balance Model and its Application in Projecting Water Supply Stress in the Conterminous US Under Future Climate Scenarios (original) (raw)
Related papers
Journal of Geophysical Research, 2011
1] We developed a water-centric monthly scale simulation model (WaSSI-C) by integrating empirical water and carbon flux measurements from the FLUXNET network and an existing water supply and demand accounting model (WaSSI). The WaSSI-C model was evaluated with basin-scale evapotranspiration (ET), gross ecosystem productivity (GEP), and net ecosystem exchange (NEE) estimates by multiple independent methods across 2103 eight-digit Hydrologic Unit Code watersheds in the conterminous United States from 2001 to 2006. Our results indicate that WaSSI-C captured the spatial and temporal variability and the effects of large droughts on key ecosystem fluxes. Our modeled mean (±standard deviation in space) ET (556 ± 228 mm yr −1 ) compared well to Moderate Resolution Imaging Spectroradiometer (MODIS) based (527 ± 251 mm yr −1 ) and watershed water balance based ET (571 ± 242 mm yr −1 ). Our mean annual GEP estimates (1362 ± 688 g C m −2 yr −1 ) compared well (R 2 = 0.83) to estimates (1194 ± 649 g C m −2 yr −1 ) by eddy flux-based EC-MOD model, but both methods led significantly higher (25-30%) values than the standard MODIS product (904 ± 467 g C m −2 yr −1 ). Among the 18 water resource regions, the southeast ranked the highest in terms of its water yield and carbon sequestration capacity. When all ecosystems were considered, the mean NEE (−353 ± 298 g C m −2 yr −1 ) predicted by this study was 60% higher than EC-MOD's estimate (−220 ± 225 g C m −2 yr −1 ) in absolute magnitude, suggesting overall high uncertainty in quantifying NEE at a large scale. Our water-centric model offers a new tool for examining the trade-offs between regional water and carbon resources under a changing environment. Citation: Sun, G., et al. (2011), Upscaling key ecosystem functions across the conterminous United States by a water-centric ecosystem model,
Robbing Peter to Pay Paul: Tradeoffs between Ecosystem Carbon Sequestration and Water Yield
Watershed Management 2010, 2010
The United States National Forest System supplies much of the nation's drinking water. However, changes in climate, land use and population are stressing the ability of these forests to provide that ecosystem service. Federal land managers are under increasing pressure to increase ecosystem carbon sequestration in an attempt to partially offset greenhouse gases and slow global warming. Unfortunately, the positive relationship between carbon gain and water use in forests, puts the need for water and increased carbon gain at odds with each other. To assess these tradeoffs, a coupled water supply and demand, carbon sequestration, and biodiversity (WaSSI-CB) model was developed. WaSSI-CB was designed to be run with climate, population, and land use change scenarios to examine the interactions between water, carbon gain and biodiversity change across the 2,100 USGS 8 digit USGS Hydrologic Unit Code watersheds that span the lower 48 US. Results from this model using historic climate and landuse data indicated that the greatest increases in water use conservation may be made through improved irrigation practices, that manipulations in forest cover (i.e., massive harvesting) are an impractical way of increasing water supply, and the that the southeastern US has the highest potential for forest carbon sequestration. Biodiversity was calculated under steady state, historic conditions, with the greatest and mammal biodiversity occurring the southern US. The impact of future climate and population change were not included in this paper due to space limitations, but will be presented at the conference.
Hydrology and Earth System Sciences Discussions
Quantifying the potential impacts of climate change on water yield and ecosystem productivity (i.e., carbon balances) is essential to developing sound watershed restoration plans, and climate change adaptation and mitigation strategies. This study links an ecohydrological model (Water Supply and Stress Index, WaSSI) with WRF (Weather Research and Forecasting Model) dynamically downscaled climate projections of the HadCM3 model under the IPCC SRES A2 emission scenario. We evaluated the future (2031–2060) changes in evapotranspiration (ET), water yield (<i>Q</i>) and gross primary productivity (GPP) from the baseline period of 1979–2007 across the 82 773 watersheds (12 digit Hydrologic Unit Code level) in the conterminous US (CONUS), and evaluated the future annual and monthly changes of hydrology and ecosystem productivity for the 18 Water Resource Regions (WRRs) or 2-digit HUCs. Across the CONUS, the future multi-year means show increases in annual precipitation (<i&g...
Modeling U.S. water resources under climate change
Earth's Future, 2014
The MIT Joint Program on the Science and Policy of Global Change combines cutting-edge scientific research with independent policy analysis to provide a solid foundation for the public and private decisions needed to mitigate and adapt to unavoidable global environmental changes. Being data-driven, the Program uses extensive Earth system and economic data and models to produce quantitative analysis and predictions of the risks of climate change and the challenges of limiting human influence on the environment-essential knowledge for the international dialogue toward a global response to climate change. To this end, the Program brings together an interdisciplinary group from two established MIT research centers: the Center for Global Change Science (CGCS) and the Center for Energy and Environmental Policy Research (CEEPR). These two centers-along with collaborators from the Marine Biology Laboratory (MBL) at Woods Hole and short-and longterm visitors-provide the united vision needed to solve global challenges. At the heart of much of the Program's work lies MIT's Integrated Global System Model. Through this integrated model, the Program seeks to: discover new interactions among natural and human climate system components; objectively assess uncertainty in economic and climate projections; critically and quantitatively analyze environmental management and policy proposals; understand complex connections among the many forces that will shape our future; and improve methods to model, monitor and verify greenhouse gas emissions and climatic impacts. This reprint is one of a series intended to communicate research results and improve public understanding of global environment and energy challenges, thereby contributing to informed debate about climate change and the economic and social implications of policy alternatives.
Journal of Applied Meteorology and Climatology, 2019
Water balance influences the distribution, abundance, and diversity of plant species across Earth’s terrestrial system. In this study, we examine changes in the water balance and, consequently, the dryland extent across eight ecoregions of the north-central United States by quantifying changes in the growing season (May–September) moisture index (MI) by 2071–99, relative to 1980–2005, under three high-resolution (~4 km) downscaled climate projections (CNRM-CM5, CCSM4, and IPSL-CM5A-MR) of high-emission scenarios (RCP8.5). We find that all ecoregions are projected to become drier as based on significant decreases in MI, except four ecoregions under CNRM-CM5, which projects relatively more moderate warming and much greater increases in precipitation relative to the other two projections. The mean projected MI across the entire study area changes by from +4% to −33%. The proportion of dryland (MI < 0.65) is projected to increase under all projections, but more significantly under th...
Remote Sensing of Environment, 2010
In this study, we used the remotely-sensed data from the Moderate Resolution Imaging Spectrometer (MODIS), meteorological and eddy flux data and an artificial neural networks (ANNs) technique to develop a daily evapotranspiration (ET) product for the period of 2004-2005 for the conterminous U.S. We then estimated and analyzed the regional water-use efficiency (WUE) based on the developed ET and MODIS gross primary production (GPP) for the region. We first trained the ANNs to predict evapotranspiration fraction (EF) based on the data at 28 AmeriFlux sites between 2003 and 2005. Five remotely-sensed variables including land surface temperature (LST), normalized difference vegetation index (NDVI), normalized difference water index (NDWI), leaf area index (LAI) and photosynthetically active radiation (PAR) and ground-measured air temperature and wind velocity were used. The daily ET was calculated by multiplying net radiation flux derived from remote sensing products with EF. We then evaluated the model performance by comparing modeled ET with the data at 24 AmeriFlux sites in 2006. We found that the ANNs predicted daily ET well (R 2 = 0.52-0.86). The ANNs were applied to predict the spatial and temporal distributions of daily ET for the conterminous U.S. in 2004 and 2005. The ecosystem WUE for the conterminous U.S. from 2004 to 2005 was calculated using MODIS GPP products (MOD17) and the estimated ET. We found that all ecosystems' WUE-drought relationships showed a two-stage pattern. Specifically, WUE increased when the intensity of drought was moderate; WUE tended to decrease under severe drought. These findings are consistent with the observations that WUE does not monotonously increase in response to water stress. Our study suggests a new water-use efficiency mechanism should be considered in ecosystem modeling. In addition, this study provides a high spatial and temporal resolution ET dataset, an important product for climate change and hydrological cycling studies for the MODIS era.
Global change biology, 2016
A cross-site analysis was conducted on seven diverse, forested watersheds in the northeastern U.S. to evaluate hydrological responses (evapotranspiration, soil moisture, seasonal and annual streamflow, and water stress) to projections of future climate. We used output from four Atmosphere-Ocean General Circulation Models (AOGCMs) (CCSM4, HadGEM2-CC, MIROC5, and MRI-CGCM3) included in Phase 5 of the Coupled Model Intercomparison Project, coupled with two Representative Concentration Pathways (RCP 8.5 and 4.5). The coarse resolution AOGCMs outputs were statistically downscaled using an asynchronous regional regression model to provide finer resolution future climate projections as inputs to the deterministic dynamic ecosystem model PnET-BGC. Simulation results indicated that projected warmer temperatures and longer growing seasons in the northeastern U.S. are anticipated to increase evapotranspiration across all sites, although invoking CO2 effects on vegetation (growth enhancement an...
Environmental Modelling & Software, 2014
The Pacific Northwest (PNW) of the conterminous United States is characterized by large variations in climate and topography, and provides an ideal geographic domain for studying interactions between regional climate and vegetation dynamics. We examined vegetation carbon (C) and water dynamics along PNW climate and topographic gradients using a process-based biogeochemical model, BIOME-BGC, the algorithms of which form bases for a fully-prognostic treatment of carbon and nitrogen cycles in Land Community Model (CLM). Simulation experiments were used to (1) analyze spatial and temporal variability of terrestrial carbon (C) stocks and flux, (2) investigate primary climatic variables controlling the variability, and (3) predict effects of future climate projections on vegetation productivity and water flux variables including evapotranspiration and water supply. The model experiments focused on two 18-year (1980e1997 and 2088e2105) simulations using future climate predictions for A2 (þ4.2 C, À7% precipitation) and B2 (1.6 C, þ11% precipitation) emissions scenarios through year 2100. Our results show large west to east spatial variations in C and water fluxes and C stocks associated with regional topography and distance from coastal areas. Interannual variability of net primary productivity (NPP) and evapotranspiration (ET) are 57% and 33%, respectively, of the 18-year mean annual fluxes for 1980e1997. The annual NPP and ET are positively correlated with precipitation but inversely proportional to vapor pressure deficit; this suggests that modeled NPP and ET are predominantly water limited in the PNW. The A2 scenario results in higher NPP and ET of 23% and 10%, respectively, and 15% lower water outflow. The B2 scenario results in higher NPP and ET of 12% and 15%, respectively, and 2% lower water outflow, despite projected increases in precipitation. Simulation experiments indicate that most PNW ecosystems are water limited, and that annual water outflow will decrease under both drier (A2) and wetter (B2) scenarios. However, higher elevations with high snowpacks of long duration may buffer the loss of water resources in some areas, even if precipitation is lower.
Journal of Geophysical Research, 2000
The land surface water balance of the continental United States is analyzed from 1963 to 1995 using a terrestrial biosphere model (IBIS), reanalysis data from NCEP/NCAR, a hydrologic routing model (HYDRA), and numerous observational data sets. Emphasis is placed on evaluating the performance of IBIS and the reanalysis, particularly over the central United States. IBIS is forced with daily climatic inputs from NCEP; an additional simulation is performed using observed precipitation. The NCEP reanalysis is found to have excessive precipitation and evapotranspiration over the central United States (particularly in the summertime), an exaggerated seasonal cycle of runoff, and low snow depths. The net surface water balance exhibits a dry bias that is corrected by nudging soil moisture toward climatology. Unfortunately, this correction term is large and appears to have a detrimental impact on other water balance components (particularly runoff). Fields that are reasonably well simulated in the reanalysis include fall and winter precipitation over the central United States, soil moisture in Illinois, and interannual variations in runoff. Results from the IBIS simulations show generally better agreement with observations than the NCEP reanalysis but continue to have nontrivial errors in certain fields. Over the central United States, these discrepancies include high winter/spring evapotranspiration (1 mm d-1 too high), low snow depth, and weak spring runoff (30-50% too low). The errors are at least partially caused by underestimated cloud cover and early spring green-up. A spatial analysis of the U.S. water balance reveals that some of the strongest seasonal and interannual variations in precipitation, evapotranspiration, and soil moisture occur over the central United States.