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Water Resources
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F.
Water Resources
[Background]
[Surface Hydrology]
[Benefits of Rainfall Enhancement]
[Hydrologic aspects of land-atmosphere]
1. Background
RAP water resource activities in 2002 included three primary areas: 1) Surface hydrology for urban flash flood analysis, 2) Hydrologic and water resource assessment of rainfall enhancement benefits in the United Arab Emirates, and 3) Land-atmosphere interactions associated with the Cooperative Atmospheric Surface Exchange Study (CASES) and the International H2O (IHOP) experiment, and the use of Geographical Information Systems in their analysis. This last objective closely ties with the 'Land-Surface/Atmospheric Interactions' section of this report, with the concurrent goal of improving our knowledge of land-surface interactions on regional weather, climate, and hydrology.
2. Surface Hydrology in Urban Flood Assessment
RAP has recently extended tools for assessing the potential impacts of heavy precipitation associated with severe weather on urban watersheds. This study applied RAP's expertise in remote sensing of precipitation with rainfall/runoff modeling, to understand the hydrometerological response of flooding events in the Denver Metropolitan Area (DMA). The study examined the hydro-meteorological conditions that existed prior to and during select flood events, addressed the quality control of radar rainfall products of the event(s) and compared it to estimates from a dense rain-gauge network. In addition, RAP's autonowcaster produced quantitative precipitation forecasts for the largest recorded flood event in Harvard Gulch in Summer 2001 (Fig. 1). These forecasts fields were used as input the to the distributed hydrologic model.
RAP scientists collected and organized watershed characteristics and flood data from the Harvard Gulch watershed in the DMA using GIS tools and applied physically-based distributed parameter hydrologic model to recreate flooding events on this watershed (Fig. 2). The Harvard Gulch watershed is a 3.6 mile area of mixed urban-use, is about twice as long as wide and is drained by a combination of storm sewers and open channels. This is an experimental watershed used by the USGS for the study of urban hydrology and hydraulics and has a long record of stream and rain-gauge data, and is thus an excellent candidate for our study. Past research has shown that when only raingages are used for precipitation estimation, different hydrologic models can produce estimated peak flows that differ from peak flow observations by as much as 260% and simulated volumes by as much as 240% for this watershed. This study examined how weather radar and rain-gauges can be used together, to better estimate peak and total storm volume discharge estimates.
Figure 1. Quantitative precipitation forecasts for the largest recorded flood event in Harvard Gulch in Summer 2001.
Figure 2. Flood data from the Harvard Gulch watershed in using GIS tools and applied physically-based distributed parameter hydrologic model to recreate flooding events on this watershed.
3. Benefits of Rainfall Enhancement - UAE
An important issue in rainfall enhancement is the determination
of the potential benefiting sectors. Sectors experiencing direct benefits
would be rainfed agriculture, forestry, and possibly social and ecosystem
services. Irrigated agriculture and municipal and industrial (M&I)
water users represent secondary benefiting sectors. In the UAE, agriculture
is solely sustained by supplemental irrigation through groundwater
withdrawals, since there is little-to-no surface water. Any rainfall
enhancement program in the UAE
would likely benefit only the secondary sectors (irrigated agriculture
and M&I water supplies) through enhancement of groundwater recharge.
Hence, rainfall enhancement for water resource benefit could be considered
"recharge enhancement." RAP scientists conducted specific
studies and analyses related to rainfall enhancement and groundwater
recharge in 2002. An overview of the UAE program can be found in the
Precipitation
Physics section.
The primary purpose of the hydrological studies was to establish, based on historical data and current observations, the relationships between rainfall and wadi flow, rainfall and impoundment levels, rainfall and groundwater levels, and the inter-relationship between these. These relationships are important for determining the future impact of rainfall increases, due to cloud seeding, on these parameters. A methodology is being developed to analyze recharge enhancement relative to the whole of the water resource system of the UAE. This analysis framework will be necessary for assisting the UAE's Department of Water Resource Studies in evaluation of any long-term project for rainfall enhancement.
Datasets made available by agencies in the UAE were used to summarize the general nature of near-surface alluvial aquifer recharge. Renewable groundwater resources were found to be derived from precipitation events large enough to sustain surface wadi flow. Flows along wadi beds can lead to localized groundwater recharge of freshwater lenses. However, little work has been done in the UAE to define the location and extent of these freshwater lenses, as most groundwater analysis has focused on 'paleo' groundwater. Water resource assessment activities in 2003 will work to address this important issue.
To perform a broad, national water resource assessment,
tools are being used and advanced, that can place into context the
costs and benefits of rainfall enhancement as a viable water resource
asset relative to other water resource investments. To accomplish
these tasks, existing RAP software tools were extended from the convective
weather group to compare
rain-gauge estimates of precipitation to radar-based estimates. A
better understanding of the nature of rainfall that leads to surface
wadi flow is important, and weather radar will be crucial for this
purpose. A major task in the 2002 UAE program was the improvement
of the weather radar for estimating precipitation. Thus, few good
gauge-radar comparisons are available for 2002, but will be a major
goal for the 2003 project.
As part of the UAE project, the Water Evaluation and Planning Model (WEAP), is being developed to allow for the comparative analysis of demand and supply components at various spatial and temporal scales (Fig. 3). WEAP is licensed by the Stockholm Environment Institute (SEI). David Yates, a RAP hydrologist, worked to help advance WEAP so it can better accommodate hydrologic processes and comparative benefit/cost analysis.
Should a randomized experiment suggest increased recharge
benefit, it will be necessary to detail and quantify a cost effective
strategy of aquifer recharge enhancement through cloud seeding, which
should be analyzed relative to other water supplies and demand management
strategies. The WEAP model allows for the detailed analysis of current
water resource supplies, their allocation and their cost of delivery,
quantification of current water resource demands, and can incorporate
projections of future demands by sector. WEAP also incorporates physical
hydrologic processes (e.g. rainfall/runoff and groundwater modeling
to assess agricultural water demands, aquifer recharge, and aquifer
depletion, and surface water / groundwater interactions).
Finally, WEAP will allow development of water demand/supply forecasts
(perhaps 5 years) of future water, the nature of the supplies, priorities
by supply to meet estimated demands, and the costs associated with
those demands.
Datasets made available by agencies in the UAE were used to summarize the general nature of near-surface alluvial aquifer recharge. Renewable groundwater resources were found to be derived from precipitation events large enough to sustain surface wadi flow. Flows along wadi beds can lead to localized groundwater recharge of freshwater lenses. However, little work has been done in the UAE to define the location and extent of these freshwater lenses, as most groundwater analysis has focused on 'paleo' groundwater. Water resource assessment activities in 2003 will work to address this important issue.
To perform a broad, national water resource assessment, tools are being used and advanced, that can place into context the costs and benefits of rainfall enhancement as a viable water resource asset relative to other water resource investments. To accomplish these tasks, existing RAP software tools were extended from the convective weather group to compare rain-gauge estimates of precipitation to radar-based estimates. A better understanding of the nature of rainfall that leads to surface wadi flow is important, and weather radar will be crucial for this purpose. A major task in the 2002 UAE program was the improvement of the weather radar for estimating precipitation. Thus, few good gauge-radar comparisons are available for 2002, but will be a major goal for the 2003 project.
As part of the UAE project, the Water Evaluation and Planning Model (WEAP), is being developed to allow for the comparative analysis of demand and supply components at various spatial and temporal scales (Fig. 3). WEAP is licensed by the Stockholm Environment Institute (SEI). David Yates, a RAP hydrologist, worked to help advance WEAP so it can better accommodate hydrologic processes and comparative benefit/cost analysis.
Figure 3. Water Evaluation and Planning Model (WEAP).
Should a randomized experiment suggest increased recharge benefit, it will be necessary to detail and quantify a cost effective strategy of aquifer recharge enhancement through cloud seeding, which should be analyzed relative to other water supplies and demand management strategies. The WEAP model allows for the detailed analysis of current water resource supplies, their allocation and their cost of delivery, and quantification of current water resource demands, and can incorporate projections of future demands by sector. WEAP also incorporates physical hydrologic processes (e.g. rainfall/runoff and groundwater modeling to assess agricultural water demands, aquifer recharge, and aquifer depletion, and surface water / groundwater interactions). Finally, WEAP will allow development of water demand/supply forecasts (perhaps 5 years) of future water, the nature of the supplies, priorities by supply to meet estimated demands, and the costs associated with those demands.
