Evaluating hydrologic effects of spatial and temporal patterns of forest canopy change using numerical modelling (original) (raw)
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Hydrological Processes, 1998
Spatially distributed rainfall±runo models, made feasible by the widespread availability of land surface characteristics data (especially digital topography), and the evolution of high power desktop workstations, are particularly useful for assessment of the hydrological eects of land surface change. Three examples are provided of the use of the Distributed Hydrology-Soil±Vegetation Model (DHSVM) to assess the hydrological eects of logging in the Paci®c Northwest. DHSVM provides a dynamic representation of the spatial distribution of soil moisture, snow cover, evapotranspiration and runo production, at the scale of digital topographic data (typically 30±100 m). Among the hydrological concerns that have been raised related to forest harvest in the Paci®c Northwest are increases in¯ood peaks owing to enhanced rain-on-snow and spring radiation melt response, and the eects of forest roads. The ®rst example is for two rain-on-snow¯oods in the North Fork Snoqualmie River during November 1990 and December 1989. Predicted maximum vegetation sensitivities (the dierence between predicted peaks for all mature vegetation compared with all clear-cut) showed a 31% increase in the peak runo for the 1989 event and a 10% increase for the larger 1990 event. The main reason for the dierence in response can be traced to less antecedent low elevation snow during the 1990 event. The second example is spring snowmelt runo for the Little Naches River, Washington, which drains the east slopes of the Washington Cascades. Analysis of spring snowmelt peak runo during May 1993 and April 1994 showed that, for current vegetation relative to all mature vegetation, increases in peak spring stream¯ow of only about 3% should have occurred over the entire basin. However, much larger increases (up to 30%) would occur for a maximum possible harvest scenario, and in a small headwaters catchment, whose higher elevation leads to greater snow coverage (and, hence, sensitivity to vegetation change) during the period of maximum runo. The third example, Hard and Ware Creeks, Washington, illustrates the eects of forest roads in two heavily logged small catchments on the western slopes of the Cascades. Use of DHSVM's road runo algorithm shows increases in peak runo for the ®ve largest events in 1992 (average observed stream¯ow of 2 . 1 m 3 s 71 ) averaging 17 . 4% for Hard Creek and 16 . 2% for Ware Creek, with a maximum percentage increase (for the largest event, in Hard Creek) of 27%. #
Hydrological Processes, 2013
In this work, we used the Regional Hydro-Ecological Simulation System (RHESSys) model to examine runoff sensitivity to land cover changes in a mountain environment. Two independent experiments were evaluated where we conducted simulations with multiple vegetation cover changes that include conversion to grass, no vegetation cover and deciduous/coniferous cover scenarios. The model experiments were performed at two hillslopes within the Weber River near Oakley, Utah watershed (USGS gauge # 10128500). Daily precipitation, air temperature and wind speed data as well as spatial data that include a digital elevation model with 30 m grid resolution, soil texture map and vegetation and land use maps were processed to drive RHESSys simulations. Observed runoff data at the watershed outlet were used for calibration and verification. Our runoff sensitivity results suggest that during winter, reduced leaf area index (LAI) decreases canopy interception resulting in increased snow accumulations and hence snow available for runoff during the early spring melt season. Increased LAI during the spring melt season tends to delay the snow melting process. This delay in snow melting process is due to reduced radiation beneath high LAI surfaces relative to low LAI surfaces. The model results suggest that annual runoff yield after removing deciduous vegetation is on average about 7% higher than with deciduous vegetation cover, while annual runoff yield after removing coniferous vegetation is on average as about 2% higher than that produced with coniferous vegetation cover. These simulations thus help quantify the sensitivity of water yield to vegetation change.
Hydrological Processes, 2013
We investigated, through hydrologic modelling, the impact of the extent and density of canopy cover on streamflow timing and on the magnitude of peak and late summer flows in the upper Tuolumne basin (2600-4000 m) of the Sierra Nevada, California, under current and warmer temperatures. We used the Distributed Hydrology Soil Vegetation Model for the hydrologic modelling of the basin, assuming four vegetation scenarios: current forest (partial cover, 80% density), all forest (uniform coverage, 80% density), all barren (no forest) and thinned forest (partial cover, 40% density) for a medium-high emissions scenario causing a 3.9 C warming over a 100-year period (2001-2100). Significant advances in streamflow timing, quantified as the centre of mass (COM) of over 1 month were projected for all vegetation scenarios. However, the COM advances faster with increased forest coverage. For example, when forest covered the entire area, the COM occurred on average 12 days earlier compared with the current forest coverage, with the rate of advance higher by about 0.06 days year À1 over 100 years and with peak and late summer flows lower by about 20% and 27%, respectively. Examination of modelled changes in energy balance components at forested and barren sites as temperatures rise indicated that increases in net longwave radiation are higher in the forest case and have a higher contribution to melting earlier in the calendar year when shortwave radiation is a smaller fraction of the energy budget. These increases contributed to increased midwinter melt under the forest at temperatures above freezing, causing decreases in total accumulation and higher winter and early spring melt rates. These results highlight the importance of carefully considering the combined impacts of changing forest cover and climate on downstream water supply and mountain ecosystems.
Hydrological Processes, 2016
Annual streamflows have decreased across mountain watersheds in the Pacific Northwest of the United States over the last~70 years; however, in some watersheds, observed annual flows have increased. Physically based models are useful tools to reveal the combined effects of climate and vegetation on long-term water balances by explicitly simulating the internal watershed hydrological fluxes that affect discharge. We used the physically based Simultaneous Heat and Water (SHAW) model to simulate the inter-annual hydrological dynamics of a 4 km 2 watershed in northern Idaho. The model simulates seasonal and annual water balance components including evaporation, transpiration, storage changes, deep drainage, and trends in streamflow. Independent measurements were used to parameterize the model, including forest transpiration, stomatal feedback to vapour pressure, forest properties (height, leaf area index, and biomass), soil properties, soil moisture, snow depth, and snow water equivalent. No calibrations were applied to fit the simulated streamflow to observations. The model reasonably simulated the annual runoff variations during the evaluation period from water year 2004 to 2009, which verified the ability of SHAW to simulate the water budget in this small watershed. The simulations indicated that inter-annual variations in streamflow were driven by variations in precipitation and soil water storage. One key parameterization issue was leaf area index, which strongly influenced interception across the catchment. This approach appears promising to help elucidate the mechanisms responsible for hydrological trends and variations resulting from climate and vegetation changes on small watersheds in the region.
Physics-based simulations of the impacts forest management practices have on hydrologic response
The impacts of logging on near-surface hydrologic response at the catchment and watershed scales were examined quantitatively using numerical simulation. The simulations were conducted with the Integrated Hydrology Model (InHM) for the North Fork of Caspar Creek Experimental Watershed, located near Fort Bragg, California. InHM is a comprehensive physics-based hydrologic-response model. The North Fork watershed (including 11 tributary catchments) is the site of an ongoing study monitoring the impacts of forest practices. InHM was parameterized and calibrated using existing data and new field measurements of soilhydraulic properties. Continuous long-term simulations were conducted for three wet seasons: before logging, after logging, and after a period of regrowth. Simulated increases in flow and peak discharges were considerably higher after clearcut harvesting. Concept-development simulations of cumulative watershed effects (CWEs) examined potential impacts of alternative timber harvest levels and methods relative to those that occurred in the North Fork watershed. Results from these simulations show that the increases in the simulated discharge after clearcutting were significant for the catchment and watershed scales and that relatively small changes in soil-hydraulic properties produced substantial changes in hydrologic response. The simulations in this study illustrate that timber harvesting can alter the streamflow generation mechanisms and patterns within a catchment.
Modeling the impact of land use change on the hydrology of a rural watershed
Journal of Hydrology, 2013
Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/authorsrights Keywords: Coupled modeling Surface-subsurface hydrology model Land use dynamics Forest growth and decay Model calibration Scenario simulation s u m m a r y Land use dynamics can have a significant impact on watershed hydrology. In this study, we develop a land use dynamics model coupled with a spatially distributed three-dimensional surface-subsurface hydrologic model. The coupled model is applied to the Bartin spring watershed, a rural watershed located in the northwestern Turkey.
Environmental Modelling and Software, 2006
This paper combines results of an empirical paired-catchment method and hydrological simulation techniques in quantifying and explaining the effect of a clear-cutting on runoff generation. The pair of catchments (56 and 24 ha) is located in the middle boreal zone in Eastern Finland. In the first part, measured runoff from the two catchments, of which one had been partly clear-cut (35%) and the other had not been treated (control), was analysed to detect differences in runoff preceding and following the cutting. In the next part, snow and canopy models were calibrated against snow water equivalent data in an open and forested environment, respectively. Output from the canopy and snow models provided an input to a hillslope hydrological model, which was parameterised for the two catchments and calibrated against runoff measurements. The hydrological model was applied to identify mechanisms that could explain the observed difference in the hydrological behaviour of the two catchments. According to the model results, both the decreased interception in the clear-cut catchment and the increased evapotranspiration in the young, growing forest in the control catchment contributed to the observed differences in spring flood volumes. During the growing season, most of the change in runoff generation between the catchments was attributed to the increased evapotranspiration in the young forest.
Journal of Hydrology, 2010
The Soil and Water Assessment Tool (SWAT) model was used to assess the implications of long-term climate trends for the hydroclimatology of the Reynolds Creek Experimental Watershed (RCEW) in the Owyhee Mountains, Idaho of the Intermountain West over a 40year period (1967-2006). Calibration and validation of the macroscale hydrology model in this highly monitored watershed is key to address the watershed processes that are vulnerable to both natural climate variability and climate change and . The model was calibrated using the streamflow data collected between 1997 and 2006 from the three nested weirs, the Reynolds Mountain East (RME) , Tollgate and Outlet. For assessing the performance of the calibrated model, this study used 30 years of streamflow data for the period between 1966 and 1996. This investigation suggested that the model predicted streamflow was best at RME, and inadequate at Outlet. Simulated soil moisture was also verified using the data available from five soil moisture measurement sites. The model was able to capture the seasonal patterns of changes in soil water storage considering the differences in the spatial extent of the observed and predicted soil water storage (point measurements against the spatially averaged values for the HRU) and uncertainty associated with the soil moisture measurements due to instrument effects. Water budget partitioning during a wet (1984) water year and a dry (1987) water year were also analyzed to characterize the differences in hydrologic cycles during the extreme hydrologic conditions. Our analysis showed that in the dry water year , vegetation at the higher elevation were under water stress by the end of the water year. Contrastingly, in the wet water year only the vegetation at low and mid elevations were under water stress whereas vegetation at the at the higher elevations derived substantial soil moisture for ET processes even towards the end of the growing season. To understand the effect of climate change on the hydrologic cycle, the observed and simulated streamflow were analyzed for trends in Center of Timing (CT). Earlier CT timings for the simulated and observed streamflow at RME weir was obvious thus manifesting global warming signals at the watershed scale level in the Intermountain west region. Observed streamflow at the Tollgate and Outlet weirs, where streamflow is partially affected by the agricultural diversions, showed later CT timings and these results appeared to suggest that climate impact assessment studies need to carefully distinguish the system behavior that is altered by both natural and humaninduced changes. the total streamflow in the intermountain west originates from the melting mountain snowpack . Therefore, accurate understanding of hydrologic processes occurring in the mountain basins is important to formulate sound water resources policies, planning and management decisions in the region. Recent trends inform us warming climate conditions and changes in both observed and predicted hydrologic cycle of the snowmelt dominated regions further amplified the importance of understanding hydrologic processes in mountain basins. Many studies have indicated that low-and mid-elevation mountainous regions including the intermountain west are more sensitive to climate warming than the higher elevations .