Abstract
Abstract. This study adopted a differential land-use/land-cover (LULC) analysis to evaluate dam-triggered land–atmosphere interactions for a number of LULC scenarios. Two specific questions were addressed: (1) can dam-triggered LULC heterogeneities modify surface and energy budget, which, in turn, change regional convergence and precipitation patterns? (2) How extensive is the modification in surface moisture and energy budget altered by dam-triggered LULC changes occurring in different climate and terrain features? The Regional Atmospheric Modeling System (RAMS, version 6.0) was set up for two climatologically and topographically contrasting regions: the American River watershed (ARW), located in California, and the Owyhee River watershed (ORW), located in eastern Oregon. For the selected atmospheric river precipitation event of 29 December 1996 to 3 January 1997, simulations of three pre-defined LULC scenarios are performed. The definition of the scenarios are (1) the "control" scenario, representing the contemporary land use, (2) the "pre-dam" scenario, representing the natural landscape before the construction of the dams and (3) the "non-irrigation" scenario, representing the condition where previously irrigated landscape in the control is transformed to the nearby land-use type. Results indicated that the ARW energy and moisture fluxes were more extensively affected by dam-induced changes in LULC than the ORW. Both regions, however, displayed commonalities in the modification of land–atmosphere processes due to LULC changes, with the control–non-irrigation scenario creating more change than the control–pre-dam scenarios. These commonalities were: (1) the combination of a decrease in temperature (up to 0.15 °C) and an increase at dew point (up to 0.25 °C) was observed; (2) there was a larger fraction of energy partitioned to latent heat flux (up to 10 W m−2) that increased the amount of water vapor in the atmosphere and resulted in a larger convective available potential energy (CAPE); (3) low-level wind-flow variation was found to be responsible for pressure gradients that affected localized circulations, moisture advection and convergence. At some locations, an increase in wind speed up to 1.6 m s−1 maximum was observed; (4) there were also areas of well-developed vertical motions responsible for moisture transport from the surface to higher altitudes that enhanced precipitation patterns in the study regions.
Highlights
LULC modifications, in the post-dam era, often lead to changes in land-surface and vegetation characteristics, such as albedo, root distribution and roughness height (Narisma and Pitman, 2003)
This study focuses on the evaluation of human–land– atmosphere interactions through a differential LULC-change analysis, for a number of pre-defined LULC scenarios using the Regional Atmospheric Modeling System (RAMS)
Through a set of ensemble experiments for both regions, a combination of cumulus parameterization and radiative schemes that best represent an observed spatial precipitation pattern were selected. These results were independently reported in the works of Woldemichael et al (2012) for American River watershed (ARW) and Woldemichael et al (2013) for Owyhee River watershed (ORW), and the reader is encouraged to refer to those works
Summary
LULC modifications, in the post-dam era, often lead to changes in land-surface (soil properties) and vegetation characteristics, such as albedo, root distribution and roughness height (Narisma and Pitman, 2003). Irrigation practices, which are one of the major post-dam LULC changes, for instance, can modify the precipitation pattern and the surface moisture and energy distribution, which alter boundary layers and regional convergence, as well as mesoscale convection (Douglas et al, 2009). The following two specific questions were addressed: (1) can LULC heterogeneities that result due to the presence of a dam modify surface and energy budget which, in turn, change regional convergence and precipitation patterns? Previous works, reported in Woldemichael et al (2012, 2013), investigated effects of land-use heterogeneities on modification of extreme precipitation for the same regions Those studies reported that there was discernible alteration of extreme precipitation that resulted from the dam-induced changes in LULC. The paper is organized as follows: Sect. 2 presents the study region; Sect. 3 explains the data and methods used in the study; Sect. 4 discusses the results; Sect. 5 presents the conclusions and recommendations of the study
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