Stakeholder participation for environmental management: A literature review

The purpose of this paper is to provide a comprehensive presentation and interpretation of the Ensemble Kalman Filter (EnKF) and its numerical implementation. The EnKF has a large user group, and numerous publications have discussed applications and theoretical aspects of it. This paper reviews the important results from these studies and also presents new ideas and alternative interpretations which further explain the success of the EnKF. In addition to providing the theoretical framework needed for using the EnKF, there is also a focus on the algorithmic formulation and optimal numerical implementation. A program listing is given for some of the key subroutines. The paper also touches upon specific issues such as the use of nonlinear measurements, in situ profiles of temperature and salinity, and data which are available with high frequency in time. An ensemble based optimal interpolation (EnOI) scheme is presented as a cost-effective approach which may serve as an alternative to the EnKF in some applications. A fairly extensive discussion is devoted to the use of time correlated model errors and the estimation of model bias.

The Ensemble Kalman Filter: Theoretical formulation and practical implementation

応用水文 = Applied hydrology

Trends in floods and low flows in the United States: impact of spatial correlation

The potential effects of climate change on the hydrology and water resources of the Colorado River basin are assessed by comparing simulated hydrologic and water resources scenarios derived from downscaled climate simulations of the U.S. Department of Energy/National Center for Atmospheric Research Parallel Climate Model (PCM) to scenarios driven by observed historical (1950–1999) climate. PCM climate scenarios include an ensemble of three 105-year future climate simulations based on projected `business-as-usual'(BAU) greenhouse gas emissions and a control climate simulation based on static 1995 greenhouse gas concentrations. Downscaled transient temperature and precipitation sequences were extracted from PCM simulations, and were used to drive the Variable Infiltration Capacity (VIC) macroscale hydrology model to produce corresponding streamflow sequences. Results for the BAU scenarios were summarized into Periods 1, 2, and 3 (2010–2039,2040–2069, 2070–2098). Average annual temperature changes for the Colorado Riverbasin were 0.5 °C warmer for control climate, and 1.0, 1.7, and 2.4 °C warmer for Periods 1–3, respectively, relative to the historicalclimate. Basin-average annual precipitation for the control climate was slightly(1%) less than for observed historical climate, and 3, 6, and 3%less for future Periods 1–3, respectively. Annual runoff in the controlrun was about 10% lower than for simulated historical conditions, and 14, 18, and 17% less for Periods 1–3, respectively. Analysis of watermanagement operations using a water management model driven by simulated streamflows showed that streamflows associated with control and future BAU climates would significantly degrade the performance of the water resourcessystem relative to historical conditions, with average total basin storage reduced by 7% for the control climate and 36, 32 and 40% for Periods 1–3, respectively. Releases from Glen Canyon Dam to the LowerBasin (mandated by the Colorado River Compact) were met in 80% of years for the control climate simulation (versus 92% in the historical climate simulation), and only in 59–75% of years for the future climate runs. Annual hydropower output was also significantly reduced for the control and future climate simulations. The high sensitivity of reservoir system performance for future climate is a reflection of the fragile equilibrium that now exists in operation of the system, with system demands only slightly less than long-term mean annual inflow.

/pdf/the-effects-of-climate-change-on-the-hydrology-and-water-4v0005hag0.pdf

The Effects of Climate Change on the Hydrology and Water Resources of the Colorado River Basin

Precipitation elasticity of streamflow, ϵP, provides a measure of the sensitivity of streamflow to changes in rainfall. Watershed model-based estimates of ϵP are shown to be highly sensitive to model structure and calibration error. A Monte Carlo experiment compares a nonparametric estimator of ϵP with various watershed model-based approaches. The nonparametric estimator is found to have low bias and is as robust as or more robust than alternate model-based approaches. The nonparametric estimator is used to construct a map of ϵP for the United States. Comparisons with 10 detailed climate change studies reveal that the contour map of ϵP introduced here provides a validation metric for past and future climate change investigations in the United States. Further investigations reveal that ϵP tends to be low for basins with significant snow accumulation and for basins whose moisture and energy inputs are seasonally in phase with one another. The Budyko hypothesis can only explain variations in ϵP for very humid basins.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2000WR900330

Climate elasticity of streamflow in the United States

As watershed models become increasingly sophisticated and useful, there is a need to extend their applicability to locations where they cannot be calibrated or validated. A new methodology for the regionalization of a watershed model is introduced and evaluated. The approach involves calibration of a watershed model to many sites in a region, concurrently. Previous research that has sought to relate the parameters of monthly water balance models to physical drainage basin characteristics in a region has met with limited success. Previous studies have taken the two-step approach: (a) estimation of watershed model parameters at each site, followed by (b) attempts to relate model parameters to drainage basin characteristics. Instead of treating these two steps as independent, both steps are implemented concurrently. All watershed models in a region are calibrated simultaneously, with the dual objective of reproducing the behaviour of observed monthly streamflows and, additionally, to obtain good rel...

https://cfpub.epa.gov/ncer_abstracts/index.cfm/fuseaction/display.files/fileID/14633

Regional calibration of a watershed model

Investigation and comparison of sampling properties of L-moments and conventional moments

[1] The overall water balance and the sensitivity of watershed runoff to changes in climate are investigated using national databases of climate and streamflow for 1,337 watersheds in the U.S. We document that 1% changes in precipitation result in 1.5–2.5% changes in watershed runoff, depending upon the degree of buffering by storage processes and other factors. Unlike previous research, our approach to estimating climate sensitivity of streamflow is nonparametric and does not depend on a hydrologic model. The upper bound for precipitation elasticity of streamflow is shown to be the inverse of the runoff ratio. For over a century, investigators [Pike, 1964; Budyko, 1974; Ol'dekop, 1911; and Schreiber, 1904] have suggested that variations in watershed aridity alone are sufficient to predict spatial variations in long-term watershed runoff. We document that variations in soil moisture holding capacity are just as important as variations in watershed aridity in explaining the mean and variance of annual watershed runoff.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2002GL015937

Hydroclimatology of the continental United States

[1] An overview of the annual hydroclimatology of the United States is provided. Time series of monthly streamflow, temperature, and precipitation are developed for 1337 watersheds in the United States. This unique data set is then used to evaluate several approaches for estimating the long-term water balance and the interannual variability of streamflow. Traditional relationships which predict either actual evapotranspiration or the interannual variability of streamflow from an aridity index are shown to perform poorly for basins with low soil moisture storage capacity. A water balance model is used to formulate new relationships for predicting actual evapotranspiration and the interannual variability of streamflow. These relationships depend on both the aridity index and a new soil moisture storage index. A physically based approach for estimating the soil moisture storage index is introduced which requires monthly time series of precipitation, potential evapotranspiration, and an estimate of maximum soil moisture holding capacity. The net results are improved expressions for the long-term water balance and the interannual variability of streamflow which do not require either calibration or streamflow data.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2001WR000619

Arumugam Sankarasubramanian

Papers

Climate elasticity of streamflow in the United States

Regional calibration of a watershed model

Investigation and comparison of sampling properties of L-moments and conventional moments

Hydroclimatology of the continental United States

Annual hydroclimatology of the United States