Assessing the Surface Energy Balance Components in the Snake River Basin

This study investigated the interaction of land-surface processes and vegetation in both natural ecosystems and irrigated agricultural lands in a semiarid region using the Noah land surface model (LSM) in combination with the Weather Research and Forecasting (WRF) Model. This study was conducted in the semiarid Snake River plains of south central Idaho comprising of both natural vegetation and agricultural lands. This area is characterized by warm, dry summers with irrigation being the main moisture source during the growing season. In order to properly represent the conditions of agricultural lands and also to investigate the effects of irrigation on land-surface processes, an irrigation algorithm was introduced into the existing LSM. Land-atmosphere feedbacks of natural vegetation were investigated through the complementary relationship between the actual evapotranspiration (ET) and the potential evapotranspiration. Results from a coupled version of the LSM enabled this research to study the effects of land surface on near-surface atmospheric properties, potential air temperature, and specific humidity. The results from this study proved the importance of including irrigation in LSMs over agricultural lands in semiarid regions. Irrigation changed the surface energy budget partitioning by increasing latent heat flux and reducing sensible heat flux. Vegetation has a greater role in partitioning the surface energy balance components. Surface cooling effects were observed through irrigation. There was a complementary behavior between LSM-simulated actual ET and potential ET computed from the North American Regional Reanalysis (NARR) data in natural vegetation during the moisture limiting periods. It was found that the sensible heat has been underestimated for croplands by the uncoupled LSM when verified against the control runs from WRF. The impact of coupling on natural vegetation was low compared to croplands and forests showing that, in croplands and forests, feedback effects of land surface to the atmosphere were more important. Land surface has significant influences on the lower atmosphere and the evolution of the planetary boundary layer

Explaining the Hydroclimatic Variability and Change in the Salmon River Basin

Climate change in the Pacific Northwest and in particular, the Salmon River Basin (SRB), is expected to bring about 3–5 °C rise in temperatures and an 8 % increase in precipitation. In order to assess the impacts due to these changes at the basin scale, this study employed an improved version of Variable Infiltration Capacity (VIC) model, which includes a parallel version of VIC combined with a comprehensive parameter estimation technique, Shuffled Complex Evolution (SCE) to estimate the streamflow and other water balance components. Our calibration (1955–1975) and validation (1976–1999) of the model at the outlet of the basin, White Bird, resulted in an r2 value of 0.94 which was considered satisfactory. Subsequent center of timing analysis showed that a gradual advancement of snowmelt induced-peak flow advancing by about 10 days in the future. Historically, the flows have shown a general decline in the basin, and in the future while the magnitudes might not be greatly affected, decreasing runoff of about 3 % over the next 90 years could be expected and timing of peak flow would shift by approximately 10 days. Also, a significant reduction of snow water equivalent up to 25 %, increased evapotranspiration up to 14 %, and decreased soil moisture storages of about 2 % is predicted by the model. A steady decline in SWE/P from the majority of climate model projections for the basin was also evident. Thus, the earlier snowmelt, decreasing soil moisture and increased evapotranspiration collectively implied the potential to trigger drought in the basin and could affect the quality of aquatic habitats and their spawning and a detailed investigation on these impacts is warranted

Evaluation of the Complementary Relationship Using Noah Land Surface Model and North American Regional Reanalysis (NARR) Data to Estimate Evapotranspiration in Semiarid Ecosystems

Estimating evapotranspiration using the complementary relationship can serve as a proxy to more sophisticated physically based approaches and can be used to better understand water and energy budget feedbacks. The authors investigated the existence of complementarity between actual evapotranspiration (ET) and potential ET (ETp) over natural vegetation in semiarid desert ecosystems of southern Idaho using only the forcing data and simulated fluxes obtained from Noah land surface model (LSM) and North American Regional Reanalysis (NARR) data. To mitigate the paucity of long-term meteorological data, the Noah LSM-simulated fluxes and the NARR forcing data were used in the advection–aridity (AA) model to derive the complementary relationship (CR) for the sagebrush and cheatgrass ecosystems. When soil moisture was a limiting factor for ET, the CR was stable and asymmetric, with b values of 2.43 and 1.43 for sagebrush and cheatgrass, respectively. Higher b values contributed to decreased ET and increased ETp, and as a result ET from the sagebrush community was less compared to that of cheatgrass. Validation of the derived CR showed that correlations between daily ET from the Noah LSM and CR-based ET were 0.76 and 0.80 for sagebrush and cheatgrass, respectively, while the root-mean-square errors were 0.53 and 0.61 mm day--1