Paul Trimble

The Atlantic Multidecadal Oscillation and its relation to rainfall and river flows in the continental U.S.

North Atlantic sea surface temperatures for 1856-1999 contain a 65-80 year cycle with a 0.4 C range, referred to as the Atlantic Multidecadal Oscillation (AMO) by Kerr (2000). AMO warm phases occurred during 1860- 1880 and 1940-1960, and cool phases during 1905-1925 and 1970-1990. The signal is global in scope, with a posi- tively correlated co-oscillation in parts of the North Pa- cic, but it is most intense in the North Atlantic and cov- ers the entire basin there. During AMO warmings most of the United States sees less than normal rainfall, including Midwest droughts in the 1930s and 1950s. Between AMO warm and cool phases, Mississippi River outflow varies by 10% while the inflow to Lake Okeechobee, Florida varies by 40%. The geographical pattern of variability is influenced mainly by changes in summer rainfall. The winter patterns of interannual rainfall variability associated with El Ni~no- Southern Oscillation are also signicantly changed between AMO phases.

Probabilistic Projection of Mean Sea Level and Coastal Extremes

AbstractFundamental uncertainties governing sea level rise projections are associated with the rate of acceleration in global sea level rise and the local factors affecting relative sea level. Recent models and observations of global ice sheets and their contributions to sea level, as well as climate models, suggest that significant sea level acceleration is imminent, yet observational data from tide gauges and satellites have not yet found rates consistent with some of the projections. To allow coastal planners a way to incorporate the uncertainties of acceleration, a synthesis of observed sea level data with selected distributions of acceleration and the current rate of rise is proposed to provide probabilistic estimates of future sea levels. The resulting distributions can be adopted in a risk-based framework to assess project vulnerability. As geophysical understanding of the climate-forced sea level dynamics improves, the selection and veracity of these distributions and their sea level projections w...

Lake Okeechobee Operations by Means of the Water Supply and Environment (WSE) Regulation Schedule

Lake Okeechobee is the second largest freshwater lake in the conterminous United States of America and is the heart of the water resources system in south Florida. The Herbert Hoover dike and several water control structures allow management of the Lake to meet different objectives, including flood control, water supply, and environmental enhancement. The regulation of the Lake water levels is performed by the U.S. Army Corps of Engineers (USACE) in consultation with the South Florida Water Management District (SFWMD). Flood control releases from Lake Okeechobee are made through the Caloosahatchee River, through the St. Lucie Canal, and southward to the Everglades. Since the early part of the 20 th century and until the middle of 2000, the Lake was operated using a variety of calendar-based regulation schedules. During the 1990s, the SFWMD and USACE conducted a study to develop and implement a more robust regulation schedule. The Water Supply and Environment (WSE) regulation schedule for Lake Okeechobee was created and it became the official operating schedule in July of 2000. Several innovative factors are introduced in WSE: Use of decision trees to guide water managers, use of indicators for current meteorological and hydrologic conditions, inclusion of seasonal and multi-seasonal hydrologic forecasting (outlooks) in the decision trees, consideration of ecological, and environmental conditions along and downstream of the release canals or rivers, etc. While still being essentially a flood release schedule, WSE was designed to improve the balance of the multiple Lake management objectives. This paper describes WSE and its weekly implementation effort. The different components and elements of WSE are presented, with the climatic and hydrologic data used in the process. Methods used to produce hydrologic outlooks are described. Additionally, the last six years of Lake Okeechobee operations under WSE are discussed. Some of the problems encountered and temporary solutions are presented.

Consideration of Climate Variability in Water Resources Planning & Operations - South Florida's Experience

Climate in any region is the r esult of both short - and long -term phenomena interacting at local, regional and global scales. In South Florida where major changes to the water resources infrastructure are being contemplated for facilitating the restoration of large -scale ecosystems suc h as the Kissimmee River Basin and the Everglades, consideration of climate variability on scales ranging from intra -seasonal to multi -decadal is extremely important in both water resources planning and regional operations. Correlations of hydro -climatolo gy of South Florida to such global phenomena as El Nino -Southern Oscillation (ENSO) and Atlantic Multi -Decadal Oscillation (AMO) have been investigated extensively. This paper provides an overview of the climatic indicators and the teleconnections that ar e significant for south Florida. In particular, the application of the research to develop regulation schedule s for the operation of Lake Okeechobee as well as the real -time implementation of rules b ased on climate outlook are discussed. The use of compu ter modeling as a tool for the design of operating rules as w ell as real -time operations is also included.

Estimation of Long -Term Reference Evapotranspiration from Regional Climate Model Datasets

Abstract Previous efforts to estimate reference evapotranspiration (ET o ) for hydrologicmodeling in South Florida have bee n limited due to the lack of distributedmeteorological data for long periods of simulation required for modeling. Recentadvances in global and regional atmospheric reanalysis and regional surfacehydrologic data assimilation have allowed for the generat ion of comprehensiveclimate dataset s that can now be used to estimate long -term ET o . Three such datasetswere evaluated and the results of such evaluation are presented here. Introduction South Florida (Figure 1) is considered a hot and humid region wher e temperaturescan exceed 32 °C for about half of the year and relative humidity usually exceeds 50%(Black, 1993). The region is very wet, with an average annual precipitation of 135 0mm/yr (Abtew et al., 200 2). About two -thirds of the precipitation falls during t herainy (wet) season which usually starts in June and ends in October. Rainfall in SouthFlorida is highly variable both spatially and temporally.Coastal areas of South Florida are characterized by an onshore sea -breeze thatdevelops during day time as a result of differential heating capacities of land andocean. This sea -breeze has the effect of modulating coastal temperatures andenhancing convection, which together with the occasional tropical systemscharacterize wet season precipitation. Th e east coast developed areas of South Floridareceive more precipitation than both interior areas and the west coast. Dry season

Use of Regional Simulation Models in Operational Hydrology in South Florida

The South Florida Water Management District (SFWMD) manages the water resources of South Florida for the benefit of the region, balancing the needs of present and future generations. The complexity of the system and the coexistence of competing water needs such as flood control, water supply and water for environmental needs, necessitate the use of appropriate water management decision tools. The SFWMD is using position analysis, a special form of risk analysis, which also has the capability of incorporating climatic forecasts into planning the seasonal operation of the system. The South Florida Water Management Model and its application in position analysis mode to investigate current and proposed operational scenarios are described in this article.