For an improved understanding of the hydrometeorological conditions of the Tana River basin of Kenya, East Africa, its joint atmospheric-terrestrial water balances are investigated. This is achieved through the application of the Weather Research and Forecasting (WRF) and the fully coupled WRF-Hydro modeling system over the MathioyaSagana subcatchment (3279 km 2 ) and its surroundings in the upper Tana River basin for 4 years (2011)(2012)(2013)(2014). The model setup consists of an outer domain at 25 km (East Africa) and an inner one at 5-km (Mathioya-Sagana subcatchment) horizontal resolution. The WRF-Hydro inner domain is enhanced with hydrological routing at 500-m horizontal resolution. The results from the fully coupled modeling system are compared to those of the WRF-only model. The coupled WRF-Hydro slightly reduces precipitation, evapotranspiration, and the soil water storage but increases runoff. The total precipitation from March to May and October to December for WRF-only (974 mm/year) and coupled WRF-Hydro (940 mm/year) is closer to that derived from the Climate Hazards Group Infrared Precipitation with Stations (CHIRPS) data (989 mm/year) than from the TRMM (795 mm/year) precipitation product. The coupled WRF-Hydro-accumulated discharge (323 mm/year) is close to that observed (333 mm/ year). However, the coupled WRF-Hydro underestimates the observed peak flows registering low but acceptable NSE (0.02) and RSR (0.99) at daily time step. The precipitation recycling and efficiency measures between WRF-only and coupled WRF-Hydro are very close and small. This suggests that most of precipitation in the region comes from moisture advection from the outside of the analysis domain, indicating a minor impact of potential land-precipitation feedback mechanisms in this case. The coupled WRF-Hydro nonetheless serves as a tool in quantifying the atmospheric-terrestrial water balance in this region.

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Water circulation patterns in a tropical mangrove-fringed bay with seagrass and coral reef are driven by tides that generate strong reversing tidal currents. The wind, which has an onshore component, generates a net clockwise-rotating eddy. The dominant tidally driven water circulation pattern, coupled with the effects of onshore wind and alongshore current generated by wave breaking, promotes the coastal trapping of turbid brackish water and its inherent nutrient content. This brackish water inundates the mangrove swamp and seagrass beds but not the coral reef ecosystem. Weak stratification prevails during the wet season in the upper parts of Kidogoweni Creek as a result of freshwater influx from rivers. In the dry season, well-mixed homogeneous water is found in most regions of the bay. A small zone of hypersaline water (salinity reaching 38 PSU) is found in the upper region of the mangrove-dominated creeks during the dry season. The connection between the mangrove swamp, with its wide salinity variations, and seagrass beds is apparently through river plumes and tidal effects. The link between seagrass beds and coral reefs is mainly through tidal influences.Research on water circulation in tropical regions is important because hydrodynamic processes influence the sustainability of marine ecological systems. Coastal water circulation also determines the interaction and therefore the linkage between coastal and marine ecosystems *through nutrients and material exchanges (Wolanski et al. 1980;Wolanski 1994;Ho 1977; Kjerfve et al. 198 1). The study of water circulation is also significant to environmentalists and land-use planners interested in determining the impact of coastal development projects on marine ecosystems. Thus, the description of coastal water circulation and exchange patterns in tropical waters is crucial to understanding the ecosystem dynamics.With that in mind, research on water circulation and its role in the linkages between mangrove, seagrass beds, and coral reef biotopes was undertaken at Gazi Bay, southern Kenya. The dominant forcings in the bay are onshore wind, tides, and river runoff, each of which vary at different periods from semidiurnal to seasonal. The strength and significance of each of these forcing functions also vary depending on a wide range of topographic, hydraulic, and meteorologic controls. In the context of linkage between eastern Africa coastal ecosystems, the role of water circulation in linking the mangroves, seagrass beds, and the coral reef ecosystems formed the central focus of the EEC-STD 3 project in Kenya. Methods and materials

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