Richard B. Lammers

Coupled Atmosphere–Biophysics–Hydrology Models for Environmental Modeling

The formulation and implementation of LEAF-2, the Land Ecosystem‐Atmosphere Feedback model, which comprises the representation of land‐surface processes in the Regional Atmospheric Modeling System (RAMS), is described. LEAF-2 is a prognostic model for the temperature and water content of soil, snow cover, vegetation, and canopy air, and includes turbulent and radiative exchanges between these components and with the atmosphere. Subdivision of a RAMS surface grid cell into multiple areas of distinct land-use types is allowed, with each subgrid area, or patch, containing its own LEAF-2 model, and each patch interacts with the overlying atmospheric column with a weight proportional to its fractional area in the grid cell. A description is also given of TOPMODEL, a land hydrology model that represents surface and subsurface downslope lateral transport of groundwater. Details of the incorporation of a modified form of TOPMODEL into LEAF-2 are presented. Sensitivity tests of the coupled system are presented that demonstrate the potential importance of the patch representation and of lateral water transport in idealized model simulations. Independent studies that have applied LEAF-2 and verified its performance against observational data are cited. Linkage of RAMS and TOPMODEL through LEAF-2 creates a modeling system that can be used to explore the coupled atmosphere‐biophysical‐ hydrologic response to altered climate forcing at local watershed and regional basin scales.

The large‐scale freshwater cycle of the Arctic

This paper synthesizes our understanding of the Arctics large-scale freshwater cycle. It combines terrestrial and oceanic observations with insights gained from the ERA-40 reanalysis and land surface and ice-ocean models. Annual mean freshwater input to the Arctic Ocean is dominated by river discharge (38%), inflow through Bering Strait (30%), and net precipitation (24%). Total freshwater export from the Arctic Ocean to the North Atlantic is dominated by transports through the Canadian Arctic Archipelago (35%) and via Fram Strait as liquid (26%) and sea ice (25%). All terms are computed relative to a reference salinity of 34.8. Compared to earlier estimates, our budget features larger import of freshwater through Bering Strait and larger liquid phase export through Fram Strait. While there is no reason to expect a steady state, error analysis indicates that the difference between annual mean oceanic inflows and outflows (∼8% of the total inflow) is indistinguishable from zero. Freshwater in the Arctic Ocean has a mean residence time of about a decade. This is understood in that annual freshwater input, while large (∼8500 km3), is an order of magnitude smaller than oceanic freshwater storage of ∼84,000 km3. Freshwater in the atmosphere, as water vapor, has a residence time of about a week. Seasonality in Arctic Ocean freshwater storage is nevertheless highly uncertain, reflecting both sparse hydrographic data and insufficient information on sea ice volume. Uncertainties mask seasonal storage changes forced by freshwater fluxes. Of flux terms with sufficient data for analysis, Fram Strait ice outflow shows the largest interannual variability.

Assessment of contemporary Arctic river runoff based on observational discharge records

We describe the contemporary hydrography of the pan-Arctic land area draining into the Arctic Ocean, northern Bering Sea, and Hudson Bay on the basis of observational records of river discharge and computed runoff. The Regional Arctic Hydrographic Network data set, R-ArcticNET, is presented, which is based on 3754 recording stations drawn from Russian, Canadian, European, and U.S. archives. R-ArcticNET represents the single largest data compendium of observed discharge in the Arctic. Approximately 73% of the nonglaciated area of the pan-Arctic is monitored by at least one river discharge gage giving a mean gage density of 168 gages per 106 km2. Average annual runoff is 212 mm yr−1 with approximately 60% of the river discharge occurring from April to July. Gridded runoff surfaces are generated for the gaged portion of the pan-Arctic region to investigate global change signals. Siberia and Alaska showed increases in winter runoff during the 1980s relative to the 1960s and 1970s during annual and seasonal periods. These changes are consistent with observations of change in the climatology of the region. Western Canada experienced decreased spring and summer runoff.

Widespread decline in hydrological monitoring threatens Pan‐Arctic Research

Operational river discharge monitoring is declining in both North America and Eurasia. This problem is especially severe in the Far East of Siberia and the province of Ontario, where 73% and 67% of river gauges were closed between 1986 and 1999, respectively. These reductions will greatly affect our ability to study variations in and alterations to the pan-Arctic hydrological cycle.

Analysis of the Arctic System for Freshwater Cycle Intensification: Observations and Expectations

Abstract Hydrologic cycle intensification is an expected manifestation of a warming climate. Although positive trends in several global average quantities have been reported, no previous studies have documented broad intensification across elements of the Arctic freshwater cycle (FWC). In this study, the authors examine the character and quantitative significance of changes in annual precipitation, evapotranspiration, and river discharge across the terrestrial pan-Arctic over the past several decades from observations and a suite of coupled general circulation models (GCMs). Trends in freshwater flux and storage derived from observations across the Arctic Ocean and surrounding seas are also described. With few exceptions, precipitation, evapotranspiration, and river discharge fluxes from observations and the GCMs exhibit positive trends. Significant positive trends above the 90% confidence level, however, are not present for all of the observations. Greater confidence in the GCM trends arises through lowe...

Geomorphometric attributes of the global system of rivers at 30-minute spatial resolution

In this paper we explore the geomorphometric characteristics and integrity of a 30 0 (longitude £ latitude) spatial resolution representation of the global system of potentially-flowing rivers. We quantify several geomorphometric attributes of digital, Simulated Topological Network (STN-30p) depicting potential flow pathways across the entire non-glacierized surface of the Earth. This data set was examined with respect to several metrics describing individual grid cells, river segments, and complete drainage systems. Nearly 60,000 grid cells constitute the global non-glacierized land mass. The cells are organized into more than 30,000 distinct river segments belonging to approximately 6200 drainage basins. STN-30p flow paths and drainage basins are classified as order one through six using the classification system of Strahler. STN-30p flow pathways depict rivers draining a global land area of 133:1 £ 10 6 km 2 . These pathways show a total length of 3:24 £ 10 6 km at 30 0 spatial resolution. The relationships between STN-30p order and interior river segment numbers, accumulated sub-basin areas, and accumulated length within individual basins yield high correlation coefficients (average r 2 . 0:96 for continents and globe). Mean values across individual continents and river orders for the bifurcation ratio (3.15 to 4.44), drainage area ratio (3.74 to 5.77), and basin length ratio (2.02 to 3.27) fall well within the ranges tabulated at finer spatial scales. A basin shape index, Sba L=A 0:5 ; defined as a function of potential mainstem length and drainage area, varies between 1.0 and 5.0 for basins .25,000 km 2 and shows a global mean of 2.12. The structure of STN-30p potential river systems is consistent with those of rivers analyzed at finer spatial scales as demonstrated by the numerical similarity of the several geomorphometric indices analyzed. However, for a particular basin, indices from STN-30p will be based on a condensed set of river orders relative to those derived at finer scales. A first order STN-30p river is roughly equivalent to an order five-to-six river derived from 1:62,500 scale maps. While 30 0 spatial resolution was found to represent well the 522 basins with areas .25,000 km 2 that drain 82% of the land mass, it cannot be used with high confidence in characterizing the geomorphometry of the remaining smaller basins. For global climate and biogeochemical studies, a composite of the 30 0 resolution and finer spatial resolutions appears to be necessary. q 2000 Elsevier

Scaling gridded river networks for macroscale hydrology: Development, analysis, and control of error

A simple and robust river network scaling algorithm (NSA) is presented to rescale fine-resolution networks to any coarser resolution. The algorithm was tested over the Danube River basin and the European continent. Coarse-resolution networks, at 2.5, 5, 10, and 30 min resolutions, were derived from higher-resolution gridded networks using NSA and geomorphometric attributes, such as river order, shape index, and width function. These parameters were calculated and compared at each resolution. Simple scaling relationships were found to predict decreasing river lengths with coarser-resolution data. This relationship can be used to correct river length as a function of grid resolution. The length-corrected width functions of the major river basins in Europe were compared at different resolutions to assess river network performance. The discretization error in representing basin area and river lengths at coarser resolutions were analyzed, and simple relationships were found to calculate the minimum number of grid cells needed to maintain the catchment area and length within a desired level of accuracy. This relationship among geomorphological characteristics, such as shape index and width function (derived from gridded networks at different resolutions), suggests that a minimum of 200 -300 grid cells is necessary to maintain the geomorphological characteristics of the river networks with sufficient accuracy.

The Dynamics of River Water Inflow to the Arctic Ocean

One of the most important components of the water budget in any ocean is the river inflow, which significantly affects the physical, chemical and biological processes of the ocean. River inflow is of special importance in the Arctic Ocean (Table 1) because although the Arctic Ocean contains only 1.0% of the world ocean water, it receives 11% of the world river runoff [1]. It is also the ocean with the largest contributing basin area to water surface area ratio (i.e. 1.5:1.0).

The Arctic Water Resource Vulnerability Index: An Integrated Assessment Tool for Community Resilience and Vulnerability with Respect to Freshwater

People in the Arctic face uncertainty in their daily lives as they contend with environmental changes at a range of scales from local to global. Freshwater is a critical resource to people, and although water resource indicators have been developed that operate from regional to global scales and for midlatitude to equatorial environments, no appropriate index exists for assessing the vulnerability of Arctic communities to changing water resources at the local scale. The Arctic Water Resource Vulnerability Index (AWRVI) is proposed as a tool that Arctic communities can use to assess their relative vulnerability–resilience to changes in their water resources from a variety of biophysical and socioeconomic processes. The AWRVI is based on a social–ecological systems perspective that includes physical and social indicators of change and is demonstrated in three case study communities/watersheds in Alaska. These results highlight the value of communities engaging in the process of using the AWRVI and the diagnostic capability of examining the suite of constituent physical and social scores rather than the total AWRVI score alone.

Flux of nutrients from Russian rivers to the Arctic Ocean: Can we establish a baseline against which to judge future changes?

Climate models predict significant warming in the Arctic in the 21st century, which will impact the functioning of terrestrial and aquatic ecosystems as well as alter land-ocean interactions in the Arctic. Because river discharge and nutrient flux integrate large-scale processes, they should be sensitive indicators of change, but detection of future changes requires knowledge of current conditions. Our objective in this paper is to evaluate the current state of affairs with respect to estimating nutrient flux to the Arctic Ocean from Russian rivers. To this end we provide estimates of contemporary (1970s–1990s) nitrate, ammonium, and phosphate fluxes to the Arctic Ocean for 15 large Russian rivers. We rely primarily on the extensive data archives of the former Soviet Union and current Russian Federation and compare these values to other estimates and to model predictions. Large discrepancies exist among the various estimates. These uncertainties must be resolved so that the scientific community will have reliable data with which to calibrate Arctic biogeochemical models and so that we will have a baseline against which to judge future changes (either natural or anthropogenic) in the Arctic watershed.