Importance Of Hydrological Processes Research Articles

Time‐Varying Sensitivity Analysis Reveals Relationships Between Watershed Climate and Variations in Annual Parameter Importance in Regions With Strong Interannual Variability

AbstractClimate change impacts on hydroclimatology are becoming increasingly apparent around the world. It is unknown how annual variations in precipitation and air temperature alter the model‐inferred importance of hydrological processes and how this varies across watersheds. To examine this, we used parsimonious rainfall‐runoff model and applied time‐varying sensitivity analysis across 30 Californian watersheds for a 33‐year period (1981–2014). We calculated annual total order sensitivity indices for five performance metrics: Kling‐Gupta Efficiency (KGE) and model error in simulating hydrologic signatures (runoff ratio, slope of flow duration curve, baseflow index, and timing of streamflow centroid). Sensitivity of hydrological signatures to the parameters differed by signature, while parameter importance with respect to KGE was much more spatially and temporally variable. Variations in parameter sensitivity with respect to KGE were either correlated with air temperature (snow‐dominated sites in the Sierra Nevada) or precipitation (lower elevation sites < 1,300 m). Across error metrics and signatures, parameter sensitivity strongly differed between wet and dry years for a subset of our study sites. While parameter importance varied through time, parameter sensitivity variations across watersheds were much more pronounced. This suggests that parameter controls on model performance are much more a reflection of watershed properties as opposed to being dominantly shaped by shifts in precipitation and air temperature. These findings emphasize the importance of understanding simulated watershed responses to fluctuating annual conditions, as this conceptual knowledge is necessary to anticipate similarities and differences in response across even relatively proximal watersheds in the face of growing extreme conditions.

A Thermal Inertia Map of Titan

AbstractLike Earth, the atmosphere of Titan, Saturn's largest moon, is affected by the ability of the surface to store and release heat. Modeling efforts have shown that global temperature distributions and wind profiles differ between simulations describing Titan's surface with a uniform thermal inertia. Cassini‐Huygens demonstrated, however, that a variety of morphologies and compositions make up the Titanian landscape. Using data from Cassini RADAR and the Visible and Infrared Mapping Spectrometer, we classified the surface into five terrain types: dune, lake, hummocky, plains, and labyrinth. We estimated the thermal and physical properties (conductivity, specific heat, and density) for each type, creating a 1° × 1° global map of thermal inertia values. For the lakes, as the depth of convection is not yet known, we considered both still and convective bodies. Four simulations of the Titan Atmospheric Model were run with different surface thermal properties: a low homogeneous thermal inertia, a moderate homogeneous, the heterogeneous map with still lakes, and the heterogeneous map with convective lakes. In dry regimes (i.e., without the hydrological cycle), the differences between the four cases were generally minimal, suggesting that general circulation models can use a single (moderate) value for surface thermal inertia value for large‐scale investigations that do not consider diurnal variations. Given the importance of hydrological processes and regional spatial diversity on Titan, future work should consider the effects of nonuniform thermal inertia on Titan's climate on local and regional scales.

Biostratinomy of Recent intertidal bivalves at False Bay, San Juan Island, Washington, U.S.A.

The importance of hydrologic processes in determining where and how a shell will be deposited is widely acknowledged, but few actualistic studies of these processes have been conducted. Additional knowledge of how the hydrologic regime influences the post-mortem distribution, orientation, and burial of modern shells can provide valuable paleoecological insights.For the purposes of biostratinomy, single and articulated shells of Macoma nasuta and Clinocardium sp. were studied in False Bay, a semicircular inlet located on the west coast of San Juan Island, WA. Dead shells of these species were the most numerous and conspicuous skeletal elements present on the tidal flats. Transects were used to quantify the valves' natural distribution, orientation and depth of burial. Shell concentrations were significantly greater toward shore and decreased toward the center of the bay. The majority of these valves were articulated (56.4%) and oriented in the convex-up attitude (71.7%).Tides and waves were the bay's dominant hydrologic forces. Spring low tides (maximum range of -0.8 m to 2.6 m) leave most of the bay subaerially exposed. During periods of immersion, waves from the Straits of Juan de Fuca underwent refraction, diffraction, and shoaling as they moved into False Bay. This influence was evidenced in the concentric sand bars which average 100 m long, 20 m wide and 0.5 m high. Painted and numbered valves were used to determine the effects of waves and tides. Shells were place in m2 areas both in a tidal channel and on a sand bar at low tide and then left for 1–2 tidal cycles. Recovery rates of shells ranged from 76.7% to 93.3%. Regardless of initial attitude, the majority were found in a convex-up attitude; convex-up valves remained in that orientation (89.8% – 97.7%) while those initially convex-down were reoriented to the convex-up position (75% – 86%). These findings confirmed that the convex-up position is the most hydrodynamically stable.The most interesting aspect of this study was the nature of valve transport. Valves placed in the tidal channel moved less than one meter while those on the sand bar showed a strong bimodal distribution: shells moved either less than 2 m or distances ranging from 10 to greater than 119 m. The long range transport was unexpected; it was caused by the flotation, under calm meteorological conditions, of subaerially exposed convex-down shells on the incoming tide. This mode of transport moved the valves considerably greater distances than either saltation or traction in bedload. Shell flotation was not correlated to valve size, handedness, nor species.