Volume 4 • Issue 5 • 1000161 J Civil Environ Eng ISSN: 2165-784X JCEE, an open access journal Yigzaw and Hossain, J Civil Environ Eng 2014, 4:5 DOI: 10.4172/2165-784X.1000161 Research Article Open Access Leveraging Precipitation Modification around Large Reservoirs in Orographic Environments for Water Resources Management Wondmagegn Yigzaw 1 * and Faisal Hossain 2 1 Department of Civil and Environmental Engineering, Tennessee Technological University, Cookeville, Tennessee, USA 2 Department of Civil and Environmental Engineering, University of Washington, Seattle, Washington, USA Abstract This research explored the possible modifcation of precipitation around large reservoirs in the Cascade Range and Sierra Nevada Mountains in the Western US where orographic precipitation is dominant. After investigating the hypothesis that an additional and man-made source of moisture, such as an artifcial reservoir and irrigated landscapes, can modify pre-dam state of orographic process on the windward side or the convective process on leeward side of the mountain, the result is interpreted in terms of better water resources management for future reservoirs. Mann-Kendall’s trend analysis and Sen’s slope estimator were applied for testing the hypothesis using historical hydrometeorological observations (precipitation, relative humidity- RH, and dew point temperature-DPTP). Four blocks of reservoirs (two from Cascade Range and two from Sierra Nevada) and six individual reservoirs were considered in this analysis. Comparison of post-dam period results for the selected reservoirs showed that atmospheric moisture content on the leeward side has a higher slope of increase than windward side. On the other hand, extreme precipitation (90th percentile and above) was found to have an increasing trend for both windward and leeward side during the post-dam era. A key conclusion of this site specifc research article is that there is an indication reservoirs in drier location (leeward side) seem to increase precipitation more than those on the windward side. This means we can make use of this extra quantity of fow volume in post-dam period for a sustainable water resource management. Such approach can be part of climate change mitigation and resilient approach to extreme events. As large reservoirs are big parts of socioeconomic development specially in economically emerging countries around the globe, new approach into dam design and operation is important. This means identifying any impact of reservoirs and land use land cover change then leverage this impact as an advantage rather than otherwise. *Corresponding author: Wondmagegn Yigzaw, Department of Civil and Environ- mental Engineering Tennessee Technological University, USA, Tel: +1-931-372- 3454; E-mail: wyyigzaw42@students.tntech.edu Received October 18, 2014; Accepted November 04, 2014; Published November 10, 2014 Citation: Yigzaw W, Hossain F (2014) Leveraging Precipitation Modifcation around Large Reservoirs in Orographic Environments for Water Resources Management. J Civil Environ Eng 4: 161. doi:10.4172/2165-784X.1000161 Copyright: © 2014 Yigzaw W, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Keywords: Orography; Artifcial reservoirs; Precipitation; Humidity; Sierra Nevada; Cascade Range Introduction Tere is an open argument that the potential change associated with construction of a dam (hereafer used alternatively with ‘reservoir’) is considered to be adverse from the perspective of climate change. Recent studies have shown the impact of these reservoirs on climate and local storm distribution [1,2] though the scale and extent of their impact is not completely understood over a variety of geophysical settings and spatial scales [3,4]. As the scientifc and engineering community is gearing towards climate change mitigation, it is worth considering resilience and sustainable plan that can address both extremes of fows for reservoirs. Tere are around 75,000 dams in the US alone with a height greater than 2m [5]. Based on the data available from Global Reservoir and Dam database (GRanD) [6], many of these dams are concentrated on large mountain ranges. Te role geographical location and topography plays on local weather formation can be leveraged in the future for changes in extreme foods. As orography is a major factor in creating climate variation on leeward and windward side of a mountainous feature [7-10], it can be hypothesized that reservoirs in the leeward side are extra moisture source which can increase the convective process hence humidity and precipitation. On the other hand the windward side has abundance of moisture which the presence of a reservoir intensifes even more. Te conventional mindset in water resources development is to capture water where it is easily available (i.e. windward side) or provide supply where regions are drier (i.e., leeward side). Te Central Valley of California is a good example where inter-basin water transfer is implemented between the Sacramento and San Joaquin river basins. Such practice can be implemented in areas where there is unbalanced water distribution, such as leeward areas. In an era of increasing climate change awareness, the relationship between topography (orographic precipitation formation) and large reservoirs has not been studied in detail. Te hypothesis that leeward reservoirs increase precipitation and humidity more than those on the windward side can be tested using the Mann-Kendall [11,12] trend analysis and Sen’s slope estimator [13]. Te West coast of the US (Sierra Nevada and Cascade Range) is an ideal area for such consideration as precipitation in the area is highly afected by orographic and convective processes during growing season (April-September). Tis area has very distinct topographical features ranging from coastal plains to mountains. Te orographic control is terrain driven and stronger on the windward side. Te convective control, which is driven more by diferential surface heating, is less sensitive to terrain and stronger on the leeward side. Folsom and Oroville Dam of California are examples of windward dams that regulate surface water fows from the Sierra Nevada Mountain (Figure 1). Owyhee, Shasta, and Weber dams in Nevada are examples on the leeward side that are used for water supply, irrigation and hydropower generation. Majority of the dams are on the western side from the Cascade Range and Sierra Nevada Mountains. Tere is sparse distribution on the leeward side of these mountain ranges. Studies on Folsom and Owyhee reservoirs have shown that the artifcial reservoir considered on the leeward side of Cascade Range (i.e., Owhyee reservoir) has infuenced extreme precipitation and food more than Folsom reservoir, which is on the windward side of J o u r n a l o f C i v il & E n v i r o n m e n t a l E n g i n e e r i n g ISSN: 2165-784X Journal of Civil & Environmental Engineering